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  <title>P1664R6: reconstructible_range - a concept for putting ranges back together</title>
<style data-fill-with="stylesheet">/******************************************************************************
 *                   Style sheet for the W3C specifications                   *
 *
 * Special classes handled by this style sheet include:
 *
 * Indices
 *   - .toc for the Table of Contents (<ol class="toc">)
 *     + <span class="secno"> for the section numbers
 *   - #toc for the Table of Contents (<nav id="toc">)
 *   - ul.index for Indices (<a href="#ref">term</a><span>, in § N.M</span>)
 *   - table.index for Index Tables (e.g. for properties or elements)
 *
 * Structural Markup
 *   - table.data for general data tables
 *     -> use 'scope' attribute, <colgroup>, <thead>, and <tbody> for best results !
 *     -> use <table class='complex data'> for extra-complex tables
 *     -> use <td class='long'> for paragraph-length cell content
 *     -> use <td class='pre'> when manual line breaks/indentation would help readability
 *   - dl.switch for switch statements
 *   - ol.algorithm for algorithms (helps to visualize nesting)
 *   - .figure and .caption (HTML4) and figure and figcaption (HTML5)
 *     -> .sidefigure for right-floated figures
 *   - ins/del
 *     -> ins/del.c### for candidate and proposed changes (amendments)
 *
 * Code
 *   - pre and code
 *
 * Special Sections
 *   - .note       for informative notes             (div, p, span, aside, details)
 *   - .example    for informative examples          (div, p, pre, span)
 *   - .issue      for issues                        (div, p, span)
 *   - .advisement for loud normative statements     (div, p, strong)
 *   - .annoying-warning for spec obsoletion notices (div, aside, details)
 *   - .correction for "candidate corrections"       (div, aside, details, section)
 *   - .addition   for "candidate additions"         (div, aside, details, section)
 *   - .correction.proposed for "proposed corrections" (div, aside, details, section)
 *   - .addition.proposed   for "proposed additions"   (div, aside, details, section)
 *
 * Definition Boxes
 *   - pre.def   for WebIDL definitions
 *   - table.def for tables that define other entities (e.g. CSS properties)
 *   - dl.def    for definition lists that define other entitles (e.g. HTML elements)
 *
 * Numbering
 *   - .secno for section numbers in .toc and headings (<span class='secno'>3.2</span>)
 *   - .marker for source-inserted example/figure/issue numbers (<span class='marker'>Issue 4</span>)
 *   - ::before styled for CSS-generated issue/example/figure numbers:
 *     -> Documents wishing to use this only need to add
 *        figcaption::before,
 *        .caption::before { content: "Figure "  counter(figure) " ";  }
 *        .example::before { content: "Example " counter(example) " "; }
 *        .issue::before   { content: "Issue "   counter(issue) " ";   }
 *
 * Header Stuff (ignore, just don't conflict with these classes)
 *   - .head for the header
 *   - .copyright for the copyright
 *
 * Outdated warning for old specs
 *
 * Miscellaneous
 *   - .overlarge for things that should be as wide as possible, even if
 *     that overflows the body text area. This can be used on an item or
 *     on its container, depending on the effect desired.
 *     Note that this styling basically doesn't help at all when printing,
 *     since A4 paper isn't much wider than the max-width here.
 *     It's better to design things to fit into a narrower measure if possible.
 *
 *   - js-added ToC jump links (see fixup.js)
 *
 ******************************************************************************/

/* color variables included separately for reliability */

/******************************************************************************/
/*                                    Body                                    */
/******************************************************************************/

	html {
	}

	body {
		counter-reset: example figure issue;

		/* Layout */
		max-width: 50em;			  /* limit line length to 50em for readability   */
		margin: 0 auto;				/* center text within page                    */
		padding: 1.6em 1.5em 2em 50px; /* assume 16px font size for downlevel clients */
		padding: 1.6em 1.5em 2em calc(26px + 1.5em); /* leave space for status flag    */

		/* Typography */
		line-height: 1.5;
		font-family: sans-serif;
		widows: 2;
		orphans: 2;
		word-wrap: break-word;
		overflow-wrap: break-word;
		hyphens: auto;

		color: black;
		color: var(--text);
		background: white top left fixed no-repeat;
		background: var(--bg) top left fixed no-repeat;
		background-size: 25px auto;
	}


/******************************************************************************/
/*                         Front Matter & Navigation                          */
/******************************************************************************/

/** Header ********************************************************************/

	div.head { margin-bottom: 1em; }
	div.head hr { border-style: solid; }

	div.head h1 {
		font-weight: bold;
		margin: 0 0 .1em;
		font-size: 220%;
	}

	div.head h2 { margin-bottom: 1.5em;}

/** W3C Logo ******************************************************************/

	.head .logo {
		float: right;
		margin: 0.4rem 0 0.2rem .4rem;
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	.head img[src*="logos/W3C"] {
		display: block;
		border: solid #1a5e9a;
		border: solid var(--logo-bg);
		border-width: .65rem .7rem .6rem;
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		background: #1a5e9a;
		background: var(--logo-bg);
		color: white;
		color: var(--logo-text);
		font-weight: bold;
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	.head a:hover > img[src*="logos/W3C"],
	.head a:focus > img[src*="logos/W3C"] {
		opacity: .8;
	}

	.head a:active > img[src*="logos/W3C"] {
		background: #c00;
		background: var(--logo-active-bg);
		border-color: #c00;
		border-color: var(--logo-active-bg);
	}

	/* see also additional rules in Link Styling section */

/** Copyright *****************************************************************/

	p.copyright,
	p.copyright small { font-size: small; }

/** Back to Top / ToC Toggle **************************************************/

	@media print {
		#toc-nav {
			display: none;
		}
	}
	@media not print {
		#toc-nav {
			position: fixed;
			z-index: 3;
			bottom: 0; left: 0;
			margin: 0;
			min-width: 1.33em;
			border-top-right-radius: 2rem;
			box-shadow: 0 0 2px;
			font-size: 1.5em;
		}
		#toc-nav > a {
			display: block;
			white-space: nowrap;

			height: 1.33em;
			padding: .1em 0.3em;
			margin: 0;

			box-shadow: 0 0 2px;
			border: none;
			border-top-right-radius: 1.33em;

			color: #707070;
			color: var(--tocnav-normal-text);
			background: white;
			background: var(--tocnav-normal-bg);
		}
		#toc-nav > a:hover,
		#toc-nav > a:focus {
			color: black;
			color: var(--tocnav-hover-text);
			background: #f8f8f8;
			background: var(--tocnav-hover-bg);
		}
		#toc-nav > a:active {
			color: #c00;
			color: var(--tocnav-active-text);
			background: white;
			background: var(--tocnav-active-bg);
		}

		#toc-nav > #toc-jump {
			padding-bottom: 2em;
			margin-bottom: -1.9em;
		}

		/* statusbar gets in the way on keyboard focus; remove once browsers fix */
		#toc-nav > a[href="#toc"]:not(:hover):focus:last-child {
			padding-bottom: 1.5rem;
		}

		#toc-nav:not(:hover) > a:not(:focus) > span + span {
			/* Ideally this uses :focus-within on #toc-nav */
			display: none;
		}
		#toc-nav > a > span + span {
			padding-right: 0.2em;
		}
	}

/** ToC Sidebar ***************************************************************/

	/* Floating sidebar */
	@media screen {
		body.toc-sidebar #toc {
			position: fixed;
			top: 0; bottom: 0;
			left: 0;
			width: 23.5em;
			max-width: 80%;
			max-width: calc(100% - 2em - 26px);
			overflow: auto;
			padding: 0 1em;
			padding-left: 42px;
			padding-left: calc(1em + 26px);
			color: black;
			color: var(--tocsidebar-text);
			background: inherit;
			background-color: #f7f8f9;
			background-color: var(--tocsidebar-bg);
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) inset;
			box-shadow: -.1em 0 .25em var(--tocsidebar-shadow) inset;
		}
		body.toc-sidebar #toc h2 {
			margin-top: .8rem;
			font-variant: small-caps;
			font-variant: all-small-caps;
			text-transform: lowercase;
			font-weight: bold;
			color: gray;
			color: hsla(203,20%,40%,.7);
			color: var(--tocsidebar-heading-text);
		}
		body.toc-sidebar #toc-jump:not(:focus) {
			width: 0;
			height: 0;
			padding: 0;
			position: absolute;
			overflow: hidden;
		}
	}
	/* Hide main scroller when only the ToC is visible anyway */
	@media screen and (max-width: 28em) {
		body.toc-sidebar {
			overflow: hidden;
		}
	}

	/* Sidebar with its own space */
	@media screen and (min-width: 78em) {
		body:not(.toc-inline) #toc {
			position: fixed;
			top: 0; bottom: 0;
			left: 0;
			width: 23.5em;
			overflow: auto;
			padding: 0 1em;
			padding-left: 42px;
			padding-left: calc(1em + 26px);
			color: black;
			color: var(--tocsidebar-text);
			background: inherit;
			background-color: #f7f8f9;
			background-color: var(--tocsidebar-bg);
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) inset;
			box-shadow: -.1em 0 .25em var(--tocsidebar-shadow) inset;
		}
		body:not(.toc-inline) #toc h2 {
			margin-top: .8rem;
			font-variant: small-caps;
			font-variant: all-small-caps;
			text-transform: lowercase;
			font-weight: bold;
			color: gray;
			color: hsla(203,20%,40%,.7);
			color: var(--tocsidebar-heading-text);
		}

		body:not(.toc-inline) {
			padding-left: 29em;
		}
		/* See also Overflow section at the bottom */

		body:not(.toc-inline) #toc-jump:not(:focus) {
			width: 0;
			height: 0;
			padding: 0;
			position: absolute;
			overflow: hidden;
		}
	}
	@media screen and (min-width: 90em) {
		body:not(.toc-inline) {
			margin: 0 4em;
		}
	}

/******************************************************************************/
/*                                Sectioning                                  */
/******************************************************************************/

/** Headings ******************************************************************/

	h1, h2, h3, h4, h5, h6, dt {
		page-break-after: avoid;
		page-break-inside: avoid;
		font: 100% sans-serif;   /* Reset all font styling to clear out UA styles */
		font-family: inherit;	/* Inherit the font family. */
		line-height: 1.2;		/* Keep wrapped headings compact */
		hyphens: manual;		/* Hyphenated headings look weird */
	}

	h2, h3, h4, h5, h6 {
		margin-top: 3rem;
	}

	h1, h2, h3 {
		color: #005A9C;
		color: var(--heading-text);
	}

	h1 { font-size: 170%; }
	h2 { font-size: 140%; }
	h3 { font-size: 120%; }
	h4 { font-weight: bold; }
	h5 { font-style: italic; }
	h6 { font-variant: small-caps; }
	dt { font-weight: bold; }

/** Subheadings ***************************************************************/

	h1 + h2,
	#profile-and-date {
		/* #profile-and-date is a subtitle in an H2 under the H1 */
		margin-top: 0;
	}
	h2 + h3,
	h3 + h4,
	h4 + h5,
	h5 + h6 {
		margin-top: 1.2em; /* = 1 x line-height */
	}

/** Section divider ***********************************************************/

	:not(.head) > :not(.head) + hr {
		font-size: 1.5em;
		text-align: center;
		margin: 1em auto;
		height: auto;
		color: black;
		color: var(--hr-text);
		border: transparent solid 0;
		background: transparent;
	}
	:not(.head) > hr::before {
		content: "\2727\2003\2003\2727\2003\2003\2727";
	}

/******************************************************************************/
/*                            Paragraphs and Lists                            */
/******************************************************************************/

	p {
		margin: 1em 0;
	}

	dd > p:first-child,
	li > p:first-child {
		margin-top: 0;
	}

	ul, ol {
		margin-left: 0;
		padding-left: 2em;
	}

	li {
		margin: 0.25em 0 0.5em;
		padding: 0;
	}

	dl dd {
		margin: 0 0 .5em 2em;
	}

	.head dd + dd { /* compact for header */
		margin-top: -.5em;
	}

	/* Style for algorithms */
	ol.algorithm ol:not(.algorithm),
	.algorithm > ol ol:not(.algorithm) {
	border-left: 0.5em solid #DEF;
	border-left: 0.5em solid var(--algo-border);
	}

	/* Put nice boxes around each algorithm. */
	[data-algorithm]:not(.heading) {
	 padding: .5em;
	 border: thin solid #ddd;
	 border: thin solid var(--algo-border);
	 border-radius: .5em;
	 margin: .5em calc(-0.5em - 1px);
	}
	[data-algorithm]:not(.heading) > :first-child {
	 margin-top: 0;
	}
	[data-algorithm]:not(.heading) > :last-child {
	 margin-bottom: 0;
	}

	/* Style for switch/case <dl>s */
	dl.switch > dd > ol.only,
	dl.switch > dd > .only > ol {
	margin-left: 0;
	}
	dl.switch > dd > ol.algorithm,
	dl.switch > dd > .algorithm > ol {
	margin-left: -2em;
	}
	dl.switch {
	padding-left: 2em;
	}
	dl.switch > dt {
	text-indent: -1.5em;
	margin-top: 1em;
	}
	dl.switch > dt + dt {
	margin-top: 0;
	}
	dl.switch > dt::before {
	content: '\21AA';
	padding: 0 0.5em 0 0;
	display: inline-block;
	width: 1em;
	text-align: right;
	line-height: 0.5em;
	}

/** Terminology Markup ********************************************************/


/******************************************************************************/
/*                                 Inline Markup                              */
/******************************************************************************/

/** Terminology Markup ********************************************************/
	dfn   { /* Defining instance */
		font-weight: bolder;
	}
	a > i { /* Instance of term */
		font-style: normal;
	}
	dt dfn code, code.idl {
		font-size: inherit;
	}
	dfn var {
		font-style: normal;
	}

/** Change Marking ************************************************************/

	del {
		color: #aa0000;
		color: var(--del-text);
		background: transparent;
		background: var(--del-bg);
		text-decoration: line-through;
	}
	ins {
		color: #006100;
		color: var(--ins-text);
		background: transparent;
		background: var(--ins-bg);
		text-decoration: underline;
	}

	/* for amendments (candidate/proposed changes) */

	.amendment ins, .correction ins, .addition ins,
	ins[class^=c] {
		text-decoration-style: dotted;
	}
	.amendment del, .correction del, .addition del,
	del[class^=c] {
		text-decoration-style: dotted;
	}
	.amendment.proposed ins, .correction.proposed ins, .addition.proposed ins,
	ins[class^=c].proposed {
		text-decoration-style: double;
	}
	.amendment.proposed del, .correction.proposed del, .addition.proposed del,
	del[class^=c].proposed {
		text-decoration-style: double;
	}

/** Miscellaneous improvements to inline formatting ***************************/

	sup {
		vertical-align: super;
		font-size: 80%
	}

/******************************************************************************/
/*                                    Code                                    */
/******************************************************************************/

/** General monospace/pre rules ***********************************************/

	pre, code, samp {
		font-family: Menlo, Consolas, "DejaVu Sans Mono", Monaco, monospace;
		font-size: .9em;
		hyphens: none;
		text-transform: none;
		text-align: left;
		text-align: start;
		font-variant: normal;
		orphans: 3;
		widows: 3;
		page-break-before: avoid;
	}
	pre code,
	code code {
		font-size: 100%;
	}

	pre {
		margin-top: 1em;
		margin-bottom: 1em;
		overflow: auto;
	}

/** Inline Code fragments *****************************************************/

	/* Do something nice. */

/******************************************************************************/
/*                                    Links                                   */
/******************************************************************************/

/** General Hyperlinks ********************************************************/

	/* We hyperlink a lot, so make it less intrusive */
	a[href] {
		color: #034575;
		color: var(--a-normal-text);
		text-decoration: underline #707070;
		text-decoration: underline var(--a-normal-underline);
		text-decoration-skip-ink: none;
	}
	a:visited {
		color: #034575;
		color: var(--a-visited-text);
		text-decoration-color: #bbb;
		text-decoration-color: var(--a-visited-underline);
	}

	/* Indicate interaction with the link */
	a[href]:focus,
	a[href]:hover {
		text-decoration-thickness: 2px;
	}
	a[href]:active {
		color: #c00;
		color: var(--a-active-text);
		text-decoration-color: #c00;
		text-decoration-color: var(--a-active-underline);
	}

	/* Backout above styling for W3C logo */
	.head .logo,
	.head .logo a {
		border: none;
		text-decoration: none;
		background: transparent;
	}

/******************************************************************************/
/*                                    Images                                  */
/******************************************************************************/

	img {
		border-style: none;
	}

	img, svg {
		/* Intentionally not color-scheme aware. */
		background: white;
	}

	/* For autogen numbers, add
	  .caption::before, figcaption::before { content: "Figure " counter(figure) ". "; }
	*/

	figure, .figure, .sidefigure {
		page-break-inside: avoid;
		text-align: center;
		margin: 2.5em 0;
	}
	.figure img,	.sidefigure img,	figure img,
	.figure object, .sidefigure object, figure object {
		max-width: 100%;
		margin: auto;
		height: auto;
	}
	.figure pre, .sidefigure pre, figure pre {
		text-align: left;
		display: table;
		margin: 1em auto;
	}
	.figure table, figure table {
		margin: auto;
	}
	@media screen and (min-width: 20em) {
		.sidefigure {
			float: right;
			width: 50%;
			margin: 0 0 0.5em 0.5em;
		}
	}
	.caption, figcaption, caption {
		font-style: italic;
		font-size: 90%;
	}
	.caption::before, figcaption::before, figcaption > .marker {
		font-weight: bold;
	}
	.caption, figcaption {
		counter-increment: figure;
	}

	/* DL list is indented 2em, but figure inside it is not */
	dd > .figure, dd > figure { margin-left: -2em; }

/******************************************************************************/
/*                             Colored Boxes                                  */
/******************************************************************************/

	.issue, .note, .example, .assertion, .advisement, blockquote,
	.amendment, .correction, .addition {
		margin: 1em auto;
		padding: .5em;
		border: .5em;
		border-left-style: solid;
		page-break-inside: avoid;
	}
	span.issue, span.note {
		padding: .1em .5em .15em;
		border-right-style: solid;
	}

	blockquote > :first-child,
	.note  > p:first-child,
	.issue > p:first-child,
	.amendment > p:first-child,
	.correction > p:first-child,
	.addition > p:first-child {
		margin-top: 0;
	}
	blockquote > :last-child,
	.note  > p:last-child,
	.issue > p:last-child,
	.amendment > p:last-child,
	.correction > p:last-child,
	.addition > p:last-child {
		margin-bottom: 0;
	}


	.issue::before, .issue > .marker,
	.example::before, .example > .marker,
	.note::before, .note > .marker,
	details.note > summary > .marker,
	.amendment::before, .amendment > .marker,
	details.amendment > summary > .marker,
	.addition::before, .addition > .marker,
	addition.amendment > summary > .marker,
	.correction::before, .correction > .marker,
	correction.amendment > summary > .marker
	{
		text-transform: uppercase;
		padding-right: 1em;
	}

	.example::before, .example > .marker {
		display: block;
		padding-right: 0em;
	}

/** Blockquotes ***************************************************************/

	blockquote {
		border-color: silver;
		border-color: var(--blockquote-border);
		background: transparent;
		background: var(--blockquote-bg);
		color: currentcolor;
		color: var(--blockquote-text);
	}

/** Open issue ****************************************************************/

	.issue {
		border-color: #e05252;
		border-color: var(--issue-border);
		background: #fbe9e9;
		background: var(--issue-bg);
		color: black;
		color: var(--issue-text);
		counter-increment: issue;
		overflow: auto;
	}
	.issue::before, .issue > .marker {
		color: #831616;
		color: var(--issueheading-text);
	}
	/* Add .issue::before { content: "Issue " counter(issue) " "; } for autogen numbers,
	  or use class="marker" to mark up the issue number in source. */

/** Example *******************************************************************/

	.example {
		border-color: #e0cb52;
		border-color: var(--example-border);
		background: #fcfaee;
		background: var(--example-bg);
		color: black;
		color: var(--example-text);
		counter-increment: example;
		overflow: auto;
		clear: both;
	}
	.example::before, .example > .marker {
		color: #574b0f;
		color: var(--exampleheading-text);
	}
	/* Add .example::before { content: "Example " counter(example) " "; } for autogen numbers,
	  or use class="marker" to mark up the example number in source. */

/** Non-normative Note ********************************************************/

	.note {
		border-color: #52e052;
		border-color: var(--note-border);
		background: #e9fbe9;
		background: var(--note-bg);
		color: black;
		color: var(--note-text);
		overflow: auto;
	}

	.note::before, .note > .marker,
	details.note > summary {
		color: hsl(120, 70%, 30%);
		color: var(--noteheading-text);
	}
	/* Add .note::before { content: "Note "; } for autogen label,
	  or use class="marker" to mark up the label in source. */

	details.note[open] > summary {
		border-bottom: 1px silver solid;
		border-bottom: 1px var(--notesummary-underline) solid;
	}

/** Assertion Box *************************************************************/
	/*  for assertions in algorithms */

	.assertion {
		border-color: #AAA;
		border-color: var(--assertion-border);
		background: #EEE;
		background: var(--assertion-bg);
		color: black;
		color: var(--assertion-text);
	}

/** Advisement Box ************************************************************/
	/*  for attention-grabbing normative statements */

	.advisement {
		border-color: orange;
		border-color: var(--advisement-border);
		border-style: none solid;
		background: #fec;
		background: var(--advisement-bg);
		color: black;
		color: var(--advisement-text);
	}
	strong.advisement {
		display: block;
		text-align: center;
	}
	.advisement::before, .advisement > .marker {
		color: #b35f00;
		color: var(--advisementheading-text);
	}

/** Amendment Box *************************************************************/

	.amendment, .correction, .addition {
		border-color: #330099;
		border-color: var(--amendment-border);
		background: #F5F0FF;
		background: var(--amendment-bg);
		color: black;
		color: var(--amendment-text);
	}
	.amendment.proposed, .correction.proposed, .addition.proposed {
		border-style: solid;
		border-block-width: 0.25em;
	}
	.amendment::before, .amendment > .marker,
	details.amendment > summary::before, details.amendment > summary > .marker,
	.correction::before, .correction > .marker,
	details.correction > summary::before, details.correction > summary > .marker,
	.addition::before, .addition > .marker,
	details.addition > summary::before, details.addition > summary > .marker {
		color: #220066;
		color: var(--amendmentheading-text);
	}
	.amendment.proposed::before, .amendment.proposed > .marker,
	details.amendment.proposed > summary::before, details.amendment.proposed > summary > .marker,
	.correction.proposed::before, .correction.proposed > .marker,
	details.correction.proposed > summary::before, details.correction.proposed > summary > .marker,
	.addition.proposed::before, .addition.proposed > .marker,
	details.addition.proposed > summary::before, details.addition.proposed > summary > .marker {
		font-weight: bold;
	}

/** Spec Obsoletion Notice ****************************************************/
	/* obnoxious obsoletion notice for older/abandoned specs. */

	details {
		display: block;
	}
	summary {
		font-weight: bolder;
	}

	.annoying-warning:not(details),
	details.annoying-warning:not([open]) > summary,
	details.annoying-warning[open] {
		background: hsla(40,100%,50%,0.95);
		background: var(--warning-bg);
		color: black;
		color: var(--warning-text);
		padding: .75em 1em;
		border: red;
		border: var(--warning-border);
		border-style: solid none;
		box-shadow: 0 2px 8px black;
		text-align: center;
	}
	.annoying-warning :last-child {
		margin-bottom: 0;
	}

@media not print {
	details.annoying-warning[open] {
		position: fixed;
		left: 0;
		right: 0;
		bottom: 2em;
		z-index: 1000;
	}
}

	details.annoying-warning:not([open]) > summary {
		text-align: center;
	}

/** Entity Definition Boxes ***************************************************/

	.def {
		padding: .5em 1em;
		background: #def;
		background: var(--def-bg);
		margin: 1.2em 0;
		border-left: 0.5em solid #8ccbf2;
		border-left: 0.5em solid var(--def-border);
		color: black;
		color: var(--def-text);
	}

/******************************************************************************/
/*                                    Tables                                  */
/******************************************************************************/

	th, td {
		text-align: left;
		text-align: start;
	}

/** Property/Descriptor Definition Tables *************************************/

	table.def {
		/* inherits .def box styling, see above */
		width: 100%;
		border-spacing: 0;
	}

	table.def td,
	table.def th {
		padding: 0.5em;
		vertical-align: baseline;
		border-bottom: 1px solid #bbd7e9;
		border-bottom: 1px solid var(--defrow-border);
	}

	table.def > tbody > tr:last-child th,
	table.def > tbody > tr:last-child td {
		border-bottom: 0;
	}

	table.def th {
		font-style: italic;
		font-weight: normal;
		padding-left: 1em;
		width: 3em;
	}

	/* For when values are extra-complex and need formatting for readability */
	table td.pre {
		white-space: pre-wrap;
	}

	/* A footnote at the bottom of a def table */
	table.def td.footnote {
		padding-top: 0.6em;
	}
	table.def td.footnote::before {
		content: " ";
		display: block;
		height: 0.6em;
		width: 4em;
		border-top: thin solid;
	}

/** Data tables (and properly marked-up index tables) *************************/
	/*
		<table class="data"> highlights structural relationships in a table
		when correct markup is used (e.g. thead/tbody, th vs. td, scope attribute)

		Use class="complex data" for particularly complicated tables --
		(This will draw more lines: busier, but clearer.)

		Use class="long" on table cells with paragraph-like contents
		(This will adjust text alignment accordingly.)
		Alternately use class="longlastcol" on tables, to have the last column assume "long".
	*/

	table {
		word-wrap: normal;
		overflow-wrap: normal;
		hyphens: manual;
	}

	table.data,
	table.index {
		margin: 1em auto;
		border-collapse: collapse;
		border: hidden;
		width: 100%;
	}
	table.data caption,
	table.index caption {
		max-width: 50em;
		margin: 0 auto 1em;
	}

	table.data td,  table.data th,
	table.index td, table.index th {
		padding: 0.5em 1em;
		border-width: 1px;
		border-color: silver;
		border-color: var(--datacell-border);
		border-top-style: solid;
	}

	table.data thead td:empty {
		padding: 0;
		border: 0;
	}

	table.data  thead,
	table.index thead,
	table.data  tbody,
	table.index tbody {
		border-bottom: 2px solid;
	}

	table.data colgroup,
	table.index colgroup {
		border-left: 2px solid;
	}

	table.data  tbody th:first-child,
	table.index tbody th:first-child  {
		border-right: 2px solid;
		border-top: 1px solid silver;
		border-top: 1px solid var(--datacell-border);
		padding-right: 1em;
	}

	table.data th[colspan],
	table.data td[colspan] {
		text-align: center;
	}

	table.complex.data th,
	table.complex.data td {
		border: 1px solid silver;
		border: 1px solid var(--datacell-border);
		text-align: center;
	}

	table.data.longlastcol td:last-child,
	table.data td.long {
		vertical-align: baseline;
		text-align: left;
	}

	table.data img {
		vertical-align: middle;
	}


/*
Alternate table alignment rules

	table.data,
	table.index {
		text-align: center;
	}

	table.data  thead th[scope="row"],
	table.index thead th[scope="row"] {
		text-align: right;
	}

	table.data  tbody th:first-child,
	table.index tbody th:first-child  {
		text-align: right;
	}

Possible extra rowspan handling

	table.data  tbody th[rowspan]:not([rowspan='1']),
	table.index tbody th[rowspan]:not([rowspan='1']),
	table.data  tbody td[rowspan]:not([rowspan='1']),
	table.index tbody td[rowspan]:not([rowspan='1']) {
		border-left: 1px solid silver;
	}

	table.data  tbody th[rowspan]:first-child,
	table.index tbody th[rowspan]:first-child,
	table.data  tbody td[rowspan]:first-child,
	table.index tbody td[rowspan]:first-child{
		border-left: 0;
		border-right: 1px solid silver;
	}
*/

/******************************************************************************/
/*                                  Indices                                   */
/******************************************************************************/


/** Table of Contents *********************************************************/

	.toc a {
		/* More spacing; use padding to make it part of the click target. */
		padding: 0.1rem 1px 0;
		/* Larger, more consistently-sized click target */
		display: block;
		/* Switch to using border-bottom for underlines */
		text-decoration: none;
		border-bottom: 1px solid;
		/* Reverse color scheme */
		color: black;
		color: var(--toclink-text);
		border-color: #3980b5;
		border-color: var(--toclink-underline);
	}
	.toc a:visited {
		color: black;
		color: var(--toclink-visited-text);
		border-color: #054572;
		border-color: var(--toclink-visited-underline);
	}
	.toc a:focus,
	.toc a:hover {
		background: rgba(75%, 75%, 75%, .25);
		background: var(--a-hover-bg);
		border-bottom-width: 3px;
		margin-bottom: -2px;
	}
	.toc a:not(:focus):not(:hover) {
		/* Allow colors to cascade through from link styling */
		border-bottom-color: transparent;
	}

	.toc, .toc ol, .toc ul, .toc li {
		list-style: none; /* Numbers must be inlined into source */
		/* because generated content isn't search/selectable and markers can't do multilevel yet */
		margin:  0;
		padding: 0;
	}
	.toc {
		line-height: 1.1em;
	}

	/* ToC not indented until third level, but font style & margins show hierarchy */
	.toc > li			{ font-weight: bold;   }
	.toc > li li		 { font-weight: normal; }
	.toc > li li li	  { font-size:   95%;	}
	.toc > li li li li	{ font-size:   90%;	}
	.toc > li li li li li { font-size:   85%;	}

	/* @supports not (display:grid) { */
		.toc > li			{ margin: 1.5rem 0;	}
		.toc > li li		 { margin: 0.3rem 0;	}
		.toc > li li li	  { margin-left: 2rem;   }

		/* Section numbers in a column of their own */
		.toc .secno {
			float: left;
			width: 4rem;
			white-space: nowrap;
		}
		.toc > li li li li .secno { font-size: 85%; }
		.toc > li li li li li .secno { font-size: 100%; }

		.toc li {
			clear: both;
		}

		:not(li) > .toc			 { margin-left:  5rem; }
		.toc .secno				 { margin-left: -5rem; }
		.toc > li li li .secno	  { margin-left: -7rem; }
		.toc > li li li li .secno	{ margin-left: -9rem; }
		.toc > li li li li li .secno { margin-left: -11rem; }

		/* Tighten up indentation in narrow ToCs */
		@media (max-width: 30em) {
			:not(li) > .toc			 { margin-left:  4rem; }
			.toc .secno				 { margin-left: -4rem; }
			.toc > li li li			 { margin-left:  1rem; }
			.toc > li li li .secno	  { margin-left: -5rem; }
			.toc > li li li li .secno	{ margin-left: -6rem; }
			.toc > li li li li li .secno { margin-left: -7rem; }
		}
		/* Loosen it on wide screens */
		@media screen and (min-width: 78em) {
			body:not(.toc-inline) :not(li) > .toc			 { margin-left:  4rem; }
			body:not(.toc-inline) .toc .secno				 { margin-left: -4rem; }
			body:not(.toc-inline) .toc > li li li			 { margin-left:  1rem; }
			body:not(.toc-inline) .toc > li li li .secno	  { margin-left: -5rem; }
			body:not(.toc-inline) .toc > li li li li .secno	{ margin-left: -6rem; }
			body:not(.toc-inline) .toc > li li li li li .secno { margin-left: -7rem; }
	}
	/* } */

	@supports (display:grid) and (display:contents) {
		/* Use #toc over .toc to override non-@supports rules. */
		#toc {
			display: grid;
			align-content: start;
			grid-template-columns: auto 1fr;
			grid-column-gap: 1rem;
			column-gap: 1rem;
			grid-row-gap: .6rem;
			row-gap: .6rem;
		}
		#toc h2 {
			grid-column: 1 / -1;
			margin-bottom: 0;
		}
		#toc ol,
		#toc li,
		#toc a {
			display: contents;
			/* Switch <a> to subgrid when supported */
		}
		#toc span {
			margin: 0;
		}
		#toc > .toc > li > a > span {
			/* The spans of the top-level list,
			  comprising the first items of each top-level section. */
			margin-top: 1.1rem;
		}
		#toc#toc .secno { /* Ugh, need more specificity to override base.css */
			grid-column: 1;
			width: auto;
			margin-left: 0;
		}
		#toc .content {
			grid-column: 2;
			width: auto;
			margin-right: 1rem;
		}
		#toc .content:hover,
		#toc .content:focus {
			background: rgba(75%, 75%, 75%, .25);
			background: var(--a-hover-bg);
			border-bottom: 3px solid #054572;
			border-bottom: 3px solid var(--toclink-underline);
			margin-bottom: -3px;
		}
		#toc li li li .content {
			margin-left: 1rem;
		}
		#toc li li li li .content {
			margin-left: 2rem;
		}
	}


/** Index *********************************************************************/

	/* Index Lists: Layout */
	ul.index	  { margin-left: 0; columns: 15em; text-indent: 1em hanging; }
	ul.index li	{ margin-left: 0; list-style: none; break-inside: avoid; }
	ul.index li li { margin-left: 1em; }
	ul.index dl	{ margin-top: 0; }
	ul.index dt	{ margin: .2em 0 .2em 20px;}
	ul.index dd	{ margin: .2em 0 .2em 40px;}
	/* Index Lists: Typography */
	ul.index ul,
	ul.index dl { font-size: smaller; }
	@media not print {
		ul.index li span:not(.dfn-paneled) {
			white-space: nowrap;
			color: transparent; }
		ul.index li a:hover + span,
		ul.index li a:focus + span {
			color: #707070;
			color: var(--indexinfo-text);
		}
	}

/** Index Tables *****************************************************/
	/* See also the data table styling section, which this effectively subclasses */

	table.index {
		font-size: small;
		border-collapse: collapse;
		border-spacing: 0;
		text-align: left;
		margin: 1em 0;
	}

	table.index td,
	table.index th {
		padding: 0.4em;
	}

	table.index tr:hover td:not([rowspan]),
	table.index tr:hover th:not([rowspan]) {
		color: black;
		color: var(--indextable-hover-text);
		background: #f7f8f9;
		background: var(--indextable-hover-bg);
	}

	/* The link in the first column in the property table (formerly a TD) */
	table.index th:first-child a {
		font-weight: bold;
	}

/** Outdated warning **********************************************************/

.outdated-spec {
	color: black;
	color: var(--outdatedspec-text);
	background-color: rgba(0,0,0,0.5);
	background-color: var(--outdatedspec-bg);
}

.outdated-warning {
	position: fixed;
	bottom: 50%;
	left: 0;
	right: 0;
	margin: 0 auto;
	width: 50%;
	background: maroon;
	background: var(--outdated-bg);
	color: white;
	color: var(--outdated-text);
	border-radius: 1em;
	box-shadow: 0 0 1em red;
	box-shadow: 0 0 1em var(--outdated-shadow);
	padding: 2em;
	text-align: center;
	z-index: 2;
}

.outdated-warning a {
	color: currentcolor;
	background: transparent;
}

.edited-rec-warning {
	background: darkorange;
	background: var(--editedrec-bg);
	box-shadow: 0 0 1em;
}

.outdated-warning button {
	color: var(--outdated-text);
	border-radius: 1em;
	box-shadow: 0 0 1em red;
	box-shadow: 0 0 1em var(--outdated-shadow);
	padding: 2em;
	text-align: center;
	z-index: 2;
}

.outdated-warning a {
	color: currentcolor;
	background: transparent;
}

.edited-rec-warning {
	background: darkorange;
	background: var(--editedrec-bg);
	box-shadow: 0 0 1em;
}

.outdated-warning button {
	position: absolute;
	top: 0;
	right:0;
	margin: 0;
	border: 0;
	padding: 0.25em 0.5em;
	background: transparent;
	color: white;
	color: var(--outdated-text);
	font:1em sans-serif;
	text-align:center;
}

.outdated-warning span {
	display: block;
}

.outdated-collapsed {
	bottom: 0;
	border-radius: 0;
	width: 100%;
	padding: 0;
}

/******************************************************************************/
/*                                    Print                                   */
/******************************************************************************/

	@media print {
		/* Pages have their own margins. */
		html {
			margin: 0;
		}
		/* Serif for print. */
		body {
			font-family: serif;
		}

		.outdated-warning {
			position: absolute;
			border-style: solid;
			border-color: red;
		}

		.outdated-warning input {
			display: none;
		}
	}
	@page {
		margin: 1.5cm 1.1cm;
	}



/******************************************************************************/
/*                             Overflow Control                               */
/******************************************************************************/

	.figure .caption, .sidefigure .caption, figcaption {
		/* in case figure is overlarge, limit caption to 50em */
		max-width: 50rem;
		margin-left: auto;
		margin-right: auto;
	}
	.overlarge {
		/* Magic to create good item positioning:
		  "content column" is 50ems wide at max; less on smaller screens.
		  Extra space (after ToC + content) is empty on the right.

		  1. When item < content column, centers item in column.
		  2. When content < item < available, left-aligns.
		  3. When item > available, fills available + scroll bar.
		*/
		display: grid;
		grid-template-columns: minmax(0, 50em);
	}
	.overlarge > table {
		/* limit preferred width of table */
		max-width: 50em;
		margin-left: auto;
		margin-right: auto;
	}

	@media (min-width: 55em) {
		.overlarge {
			margin-right: calc(13px + 26.5rem - 50vw);
			max-width: none;
		}
	}
	@media screen and (min-width: 78em) {
		body:not(.toc-inline) .overlarge {
			/* 30.5em body padding 50em content area */
			margin-right: calc(40em - 50vw) !important;
		}
	}
	@media screen and (min-width: 90em) {
		body:not(.toc-inline) .overlarge {
			/* 4em html margin 30.5em body padding 50em content area */
			margin-right: calc(84.5em - 100vw) !important;
		}
	}

	@media not print {
		.overlarge {
			overflow-x: auto;
			/* See Lea Verou's explanation background-attachment:
			* http://lea.verou.me/2012/04/background-attachment-local/
			*
			background: top left  / 4em 100% linear-gradient(to right,  #ffffff, rgba(255, 255, 255, 0)) local,
						top right / 4em 100% linear-gradient(to left, #ffffff, rgba(255, 255, 255, 0)) local,
						top left  / 1em 100% linear-gradient(to right,  #c3c3c5, rgba(195, 195, 197, 0)) scroll,
						top right / 1em 100% linear-gradient(to left, #c3c3c5, rgba(195, 195, 197, 0)) scroll,
						white;
			background-repeat: no-repeat;
			*/
		}
	}
</style>
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    blockquote c-[sx] { color: inherit; } /* Literal.String.Other */
    blockquote c-[sr] { color: inherit; } /* Literal.String.Regex */
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    blockquote c-[vc] { color: inherit; } /* Name.Variable.Class */
    blockquote c-[vg] { color: inherit; } /* Name.Variable.Global */
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<pre class=include-raw line-number=-1 path='resources/css/wording.css'></pre></style>
<style>
@media (prefers-color-scheme: dark) {
	:root {
		--bg-color: rgba(0, 0, 0, 0);
	}

	ins { background: rgba(0, 20, 0); color: rgba(115, 255, 110); }
	del { background: rgba(20, 0, 0); color: rgb(255, 124, 124); text-decoration: line-through; }
	recent-ins { background: rgba(0, 20, 0); color: rgba(80, 80, 255); }
	recent-del { background: rgba(20, 0, 0); color: rgb(255, 156, 56); text-decoration: line-through; }
	blockquote .highlight:not(.idl) { padding: 0.5em }
	blockquote ins .highlight:not(.idl) { background: rgba( 0, 20, 0); }
	blockquote del .highlight:not(.idl) { background: rgba(20,  0, 0); }
	blockquote code.highlight:not(.idl) { background: inherit; padding: initial; }

	c-[a] { color: #e783b4 } /* Keyword.Declaration */
	c-[b] { color: #e783b4 } /* Keyword.Type */
	c-[c] { color: #6ad4cc } /* Comment */
	c-[d] { color: #6ad4cc } /* Comment.Multiline */
	c-[e] { color: #92cbf5 } /* Name.Attribute */
	c-[f] { color: #b58900 } /* Name.Tag */
	c-[g] { color: #cb4b16 } /* Name.Variable */
	c-[k] { color: #e783b4 } /* Keyword */
	c-[l] { color: #a2b1b6 } /* Literal */
	c-[m] { color: #a2b1b6 } /* Literal.Number */
	c-[n] { color: #92cbf5 } /* Name */
	c-[o] { color: #a2b1b6 } /* Operator */
	c-[p] { color: #a2b1b6 } /* Punctuation */
	c-[s] { color: #a0a3e5 } /* Literal.String */
	c-[t] { color: #a0a3e5 } /* Literal.String.Single */
	c-[u] { color: #a0a3e5 } /* Literal.String.Double */
	c-[ch] { color: #6ad4cc } /* Comment.Hashbang */
	c-[cp] { color: #6ad4cc } /* Comment.Preproc */
	c-[cpf] { color: #6ad4cc } /* Comment.PreprocFile */
	c-[c1] { color: #6ad4cc } /* Comment.Single */
	c-[cs] { color: #6ad4cc } /* Comment.Special */
	c-[kc] { color: #e783b4 } /* Keyword.Constant */
	c-[kn] { color: #e783b4 } /* Keyword.Namespace */
	c-[kp] { color: #e783b4 } /* Keyword.Pseudo */
	c-[kr] { color: #e783b4 } /* Keyword.Reserved */
	c-[ld] { color: #a2b1b6 } /* Literal.Date */
	c-[nc] { color: #92cbf5 } /* Name.Class */
	c-[no] { color: #92cbf5 } /* Name.Constant */
	c-[nd] { color: #92cbf5 } /* Name.Decorator */
	c-[ni] { color: #92cbf5 } /* Name.Entity */
	c-[ne] { color: #92cbf5 } /* Name.Exception */
	c-[nf] { color: #92cbf5 } /* Name.Function */
	c-[nl] { color: #92cbf5 } /* Name.Label */
	c-[nn] { color: #92cbf5 } /* Name.Namespace */
	c-[py] { color: #92cbf5 } /* Name.Property */
	c-[ow] { color: #a2b1b6 } /* Operator.Word */
	c-[mb] { color: #a2b1b6 } /* Literal.Number.Bin */
	c-[mf] { color: #a2b1b6 } /* Literal.Number.Float */
	c-[mh] { color: #a2b1b6 } /* Literal.Number.Hex */
	c-[mi] { color: #a2b1b6 } /* Literal.Number.Integer */
	c-[mo] { color: #a2b1b6 } /* Literal.Number.Oct */
	c-[sa] { color: #a0a3e5 } /* Literal.String.Affix */
	c-[sb] { color: #a0a3e5 } /* Literal.String.Backtick */
	c-[sc] { color: #a0a3e5 } /* Literal.String.Char */
	c-[dl] { color: #a0a3e5 } /* Literal.String.Delimiter */
	c-[sd] { color: #a0a3e5 } /* Literal.String.Doc */
	c-[se] { color: #a0a3e5 } /* Literal.String.Escape */
	c-[sh] { color: #a0a3e5 } /* Literal.String.Heredoc */
	c-[si] { color: #a0a3e5 } /* Literal.String.Interpol */
	c-[sx] { color: #a0a3e5 } /* Literal.String.Other */
	c-[sr] { color: #a0a3e5 } /* Literal.String.Regex */
	c-[ss] { color: #a0a3e5 } /* Literal.String.Symbol */
	c-[fm] { color: #92cbf5 } /* Name.Function.Magic */
	c-[vc] { color: #cb4b16 } /* Name.Variable.Class */
	c-[vg] { color: #cb4b16 } /* Name.Variable.Global */
	c-[vi] { color: #cb4b16 } /* Name.Variable.Instance */
	c-[vm] { color: #cb4b16 } /* Name.Variable.Magic */
	c-[il] { color: #a2b1b6 } /* Literal.Number.Integer.Long */

	blockquote c-[b] { color: #e783b4 } /* Keyword.Type */
	blockquote c-[a] { color: #e783b4 } /* Keyword.Declaration */
	blockquote c-[c] { color: #6ad4cc } /* Comment */
	blockquote c-[d] { color: #6ad4cc } /* Comment.Multiline */
	blockquote c-[e] { color: #92cbf5 } /* Name.Attribute */
	blockquote c-[f] { color: #b58900 } /* Name.Tag */
	blockquote c-[g] { color: #cb4b16 } /* Name.Variable */
	blockquote c-[k] { color: #e783b4 } /* Keyword */
	blockquote c-[l] { color: #a2b1b6 } /* Literal */
	blockquote c-[m] { color: #a2b1b6 } /* Literal.Number */
	blockquote c-[n] { color: #92cbf5 } /* Name */
	blockquote c-[o] { color: #a2b1b6 } /* Operator */
	blockquote c-[p] { color: #a2b1b6 } /* Punctuation */
	blockquote c-[s] { color: #a0a3e5 } /* Literal.String */
	blockquote c-[t] { color: #a0a3e5 } /* Literal.String.Single */
	blockquote c-[u] { color: #a0a3e5 } /* Literal.String.Double */
	blockquote c-[ch] { color: #6ad4cc } /* Comment.Hashbang */
	blockquote c-[cp] { color: #6ad4cc } /* Comment.Preproc */
	blockquote c-[cpf] { color: #6ad4cc } /* Comment.PreprocFile */
	blockquote c-[c1] { color: #6ad4cc } /* Comment.Single */
	blockquote c-[cs] { color: #6ad4cc } /* Comment.Special */
	blockquote c-[kc] { color: #e783b4 } /* Keyword.Constant */
	blockquote c-[kn] { color: #e783b4 } /* Keyword.Namespace */
	blockquote c-[kp] { color: #e783b4 } /* Keyword.Pseudo */
	blockquote c-[kr] { color: #e783b4 } /* Keyword.Reserved */
	blockquote c-[ld] { color: #a2b1b6 } /* Literal.Date */
	blockquote c-[nc] { color: #92cbf5 } /* Name.Class */
	blockquote c-[no] { color: #92cbf5 } /* Name.Constant */
	blockquote c-[nd] { color: #92cbf5 } /* Name.Decorator */
	blockquote c-[ni] { color: #92cbf5 } /* Name.Entity */
	blockquote c-[ne] { color: #92cbf5 } /* Name.Exception */
	blockquote c-[nf] { color: #92cbf5 } /* Name.Function */
	blockquote c-[nl] { color: #92cbf5 } /* Name.Label */
	blockquote c-[nn] { color: #92cbf5 } /* Name.Namespace */
	blockquote c-[py] { color: #92cbf5 } /* Name.Property */
	blockquote c-[ow] { color: #a2b1b6 } /* Operator.Word */
	blockquote c-[mb] { color: #a2b1b6 } /* Literal.Number.Bin */
	blockquote c-[mf] { color: #a2b1b6 } /* Literal.Number.Float */
	blockquote c-[mh] { color: #a2b1b6 } /* Literal.Number.Hex */
	blockquote c-[mi] { color: #a2b1b6 } /* Literal.Number.Integer */
	blockquote c-[mo] { color: #a2b1b6 } /* Literal.Number.Oct */
	blockquote c-[sa] { color: #a0a3e5 } /* Literal.String.Affix */
	blockquote c-[sb] { color: #a0a3e5 } /* Literal.String.Backtick */
	blockquote c-[sc] { color: #a0a3e5 } /* Literal.String.Char */
	blockquote c-[dl] { color: #a0a3e5 } /* Literal.String.Delimiter */
	blockquote c-[sd] { color: #a0a3e5 } /* Literal.String.Doc */
	blockquote c-[se] { color: #a0a3e5 } /* Literal.String.Escape */
	blockquote c-[sh] { color: #a0a3e5 } /* Literal.String.Heredoc */
	blockquote c-[si] { color: #a0a3e5 } /* Literal.String.Interpol */
	blockquote c-[sx] { color: #a0a3e5 } /* Literal.String.Other */
	blockquote c-[sr] { color: #a0a3e5 } /* Literal.String.Regex */
	blockquote c-[ss] { color: #a0a3e5 } /* Literal.String.Symbol */
	blockquote c-[fm] { color: #92cbf5 } /* Name.Function.Magic */
	blockquote c-[vc] { color: #cb4b16 } /* Name.Variable.Class */
	blockquote c-[vg] { color: #cb4b16 } /* Name.Variable.Global */
	blockquote c-[vi] { color: #cb4b16 } /* Name.Variable.Instance */
	blockquote c-[vm] { color: #cb4b16 } /* Name.Variable.Magic */
	blockquote c-[il] { color: #a2b1b6 } /* Literal.Number.Integer.Long */
}

@media (prefers-color-scheme: light) {
	:root {
		--bg-color: rgba(255, 255, 255, 0);
	}
	ins { background: rgba(200, 255, 200); color: rgba(0, 20, 0); }
	del { background: rgba(255, 200, 200); color: rgb(20, 0, 0); text-decoration: line-through; }
	blockquote .highlight:not(.idl) { padding: 0.5em }
	blockquote ins .highlight:not(.idl) { background: rgba(200, 255, 200); }
	blockquote del .highlight:not(.idl) { background: rgba(255, 200, 200); }
	blockquote code.highlight:not(.idl) { background: inherit; padding: initial; }
}
</style>
<style>/* style-autolinks */

.css.css, .property.property, .descriptor.descriptor {
    color: var(--a-normal-text);
    font-size: inherit;
    font-family: inherit;
}
.css::before, .property::before, .descriptor::before {
    content: "‘";
}
.css::after, .property::after, .descriptor::after {
    content: "’";
}
.property, .descriptor {
    /* Don't wrap property and descriptor names */
    white-space: nowrap;
}
.type { /* CSS value <type> */
    font-style: italic;
}
pre .property::before, pre .property::after {
    content: "";
}
[data-link-type="property"]::before,
[data-link-type="propdesc"]::before,
[data-link-type="descriptor"]::before,
[data-link-type="value"]::before,
[data-link-type="function"]::before,
[data-link-type="at-rule"]::before,
[data-link-type="selector"]::before,
[data-link-type="maybe"]::before {
    content: "‘";
}
[data-link-type="property"]::after,
[data-link-type="propdesc"]::after,
[data-link-type="descriptor"]::after,
[data-link-type="value"]::after,
[data-link-type="function"]::after,
[data-link-type="at-rule"]::after,
[data-link-type="selector"]::after,
[data-link-type="maybe"]::after {
    content: "’";
}

[data-link-type].production::before,
[data-link-type].production::after,
.prod [data-link-type]::before,
.prod [data-link-type]::after {
    content: "";
}

[data-link-type=element],
[data-link-type=element-attr] {
    font-family: Menlo, Consolas, "DejaVu Sans Mono", monospace;
    font-size: .9em;
}
[data-link-type=element]::before { content: "<" }
[data-link-type=element]::after  { content: ">" }

[data-link-type=biblio] {
    white-space: pre;
}</style>
<style>/* style-colors */

/* Any --*-text not paired with a --*-bg is assumed to have a transparent bg */
:root {
    color-scheme: light dark;

    --text: black;
    --bg: white;

    --unofficial-watermark: url(https://www.w3.org/StyleSheets/TR/2016/logos/UD-watermark);

    --logo-bg: #1a5e9a;
    --logo-active-bg: #c00;
    --logo-text: white;

    --tocnav-normal-text: #707070;
    --tocnav-normal-bg: var(--bg);
    --tocnav-hover-text: var(--tocnav-normal-text);
    --tocnav-hover-bg: #f8f8f8;
    --tocnav-active-text: #c00;
    --tocnav-active-bg: var(--tocnav-normal-bg);

    --tocsidebar-text: var(--text);
    --tocsidebar-bg: #f7f8f9;
    --tocsidebar-shadow: rgba(0,0,0,.1);
    --tocsidebar-heading-text: hsla(203,20%,40%,.7);

    --toclink-text: var(--text);
    --toclink-underline: #3980b5;
    --toclink-visited-text: var(--toclink-text);
    --toclink-visited-underline: #054572;

    --heading-text: #005a9c;

    --hr-text: var(--text);

    --algo-border: #def;

    --del-text: red;
    --del-bg: transparent;
    --ins-text: #080;
    --ins-bg: transparent;

    --a-normal-text: #034575;
    --a-normal-underline: #bbb;
    --a-visited-text: var(--a-normal-text);
    --a-visited-underline: #707070;
    --a-hover-bg: rgba(75%, 75%, 75%, .25);
    --a-active-text: #c00;
    --a-active-underline: #c00;

    --blockquote-border: silver;
    --blockquote-bg: transparent;
    --blockquote-text: currentcolor;

    --issue-border: #e05252;
    --issue-bg: #fbe9e9;
    --issue-text: var(--text);
    --issueheading-text: #831616;

    --example-border: #e0cb52;
    --example-bg: #fcfaee;
    --example-text: var(--text);
    --exampleheading-text: #574b0f;

    --note-border: #52e052;
    --note-bg: #e9fbe9;
    --note-text: var(--text);
    --noteheading-text: hsl(120, 70%, 30%);
    --notesummary-underline: silver;

    --assertion-border: #aaa;
    --assertion-bg: #eee;
    --assertion-text: black;

    --advisement-border: orange;
    --advisement-bg: #fec;
    --advisement-text: var(--text);
    --advisementheading-text: #b35f00;

    --warning-border: red;
    --warning-bg: hsla(40,100%,50%,0.95);
    --warning-text: var(--text);

    --amendment-border: #330099;
    --amendment-bg: #F5F0FF;
    --amendment-text: var(--text);
    --amendmentheading-text: #220066;

    --def-border: #8ccbf2;
    --def-bg: #def;
    --def-text: var(--text);
    --defrow-border: #bbd7e9;

    --datacell-border: silver;

    --indexinfo-text: #707070;

    --indextable-hover-text: black;
    --indextable-hover-bg: #f7f8f9;

    --outdatedspec-bg: rgba(0, 0, 0, .5);
    --outdatedspec-text: black;
    --outdated-bg: maroon;
    --outdated-text: white;
    --outdated-shadow: red;

    --editedrec-bg: darkorange;
}</style>
<style>/* style-counters */

body {
    counter-reset: example figure issue;
}
.issue {
    counter-increment: issue;
}
.issue:not(.no-marker)::before {
    content: "Issue " counter(issue);
}

.example {
    counter-increment: example;
}
.example:not(.no-marker)::before {
    content: "Example " counter(example);
}
.invalid.example:not(.no-marker)::before,
.illegal.example:not(.no-marker)::before {
    content: "Invalid Example" counter(example);
}

figcaption {
    counter-increment: figure;
}
figcaption:not(.no-marker)::before {
    content: "Figure " counter(figure) " ";
}</style>
<style>/* style-issues */

a[href].issue-return {
    float: right;
    float: inline-end;
    color: var(--issueheading-text);
    font-weight: bold;
    text-decoration: none;
}
</style>
<style>/* style-md-lists */

/* This is a weird hack for me not yet following the commonmark spec
   regarding paragraph and lists. */
[data-md] > :first-child {
    margin-top: 0;
}
[data-md] > :last-child {
    margin-bottom: 0;
}</style>
<style>/* style-selflinks */

:root {
    --selflink-text: white;
    --selflink-bg: gray;
    --selflink-hover-text: black;
}
.heading, .issue, .note, .example, li, dt {
    position: relative;
}
a.self-link {
    position: absolute;
    top: 0;
    left: calc(-1 * (3.5rem - 26px));
    width: calc(3.5rem - 26px);
    height: 2em;
    text-align: center;
    border: none;
    transition: opacity .2s;
    opacity: .5;
}
a.self-link:hover {
    opacity: 1;
}
.heading > a.self-link {
    font-size: 83%;
}
li > a.self-link {
    left: calc(-1 * (3.5rem - 26px) - 2em);
}
dfn > a.self-link {
    top: auto;
    left: auto;
    opacity: 0;
    width: 1.5em;
    height: 1.5em;
    background: var(--selflink-bg);
    color: var(--selflink-text);
    font-style: normal;
    transition: opacity .2s, background-color .2s, color .2s;
}
dfn:hover > a.self-link {
    opacity: 1;
}
dfn > a.self-link:hover {
    color: var(--selflink-hover-text);
}

a.self-link::before            { content: "¶"; }
.heading > a.self-link::before { content: "§"; }
dfn > a.self-link::before      { content: "#"; }
</style>
<style>/* style-syntax-highlighting */

code.highlight { padding: .1em; border-radius: .3em; }
pre.highlight, pre > code.highlight { display: block; padding: 1em; margin: .5em 0; overflow: auto; border-radius: 0; }

.highlight:not(.idl) { background: rgba(0, 0, 0, .03); }
c-[a] { color: #990055 } /* Keyword.Declaration */
c-[b] { color: #990055 } /* Keyword.Type */
c-[c] { color: #708090 } /* Comment */
c-[d] { color: #708090 } /* Comment.Multiline */
c-[e] { color: #0077aa } /* Name.Attribute */
c-[f] { color: #669900 } /* Name.Tag */
c-[g] { color: #222222 } /* Name.Variable */
c-[k] { color: #990055 } /* Keyword */
c-[l] { color: #000000 } /* Literal */
c-[m] { color: #000000 } /* Literal.Number */
c-[n] { color: #0077aa } /* Name */
c-[o] { color: #999999 } /* Operator */
c-[p] { color: #999999 } /* Punctuation */
c-[s] { color: #a67f59 } /* Literal.String */
c-[t] { color: #a67f59 } /* Literal.String.Single */
c-[u] { color: #a67f59 } /* Literal.String.Double */
c-[cp] { color: #708090 } /* Comment.Preproc */
c-[c1] { color: #708090 } /* Comment.Single */
c-[cs] { color: #708090 } /* Comment.Special */
c-[kc] { color: #990055 } /* Keyword.Constant */
c-[kn] { color: #990055 } /* Keyword.Namespace */
c-[kp] { color: #990055 } /* Keyword.Pseudo */
c-[kr] { color: #990055 } /* Keyword.Reserved */
c-[ld] { color: #000000 } /* Literal.Date */
c-[nc] { color: #0077aa } /* Name.Class */
c-[no] { color: #0077aa } /* Name.Constant */
c-[nd] { color: #0077aa } /* Name.Decorator */
c-[ni] { color: #0077aa } /* Name.Entity */
c-[ne] { color: #0077aa } /* Name.Exception */
c-[nf] { color: #0077aa } /* Name.Function */
c-[nl] { color: #0077aa } /* Name.Label */
c-[nn] { color: #0077aa } /* Name.Namespace */
c-[py] { color: #0077aa } /* Name.Property */
c-[ow] { color: #999999 } /* Operator.Word */
c-[mb] { color: #000000 } /* Literal.Number.Bin */
c-[mf] { color: #000000 } /* Literal.Number.Float */
c-[mh] { color: #000000 } /* Literal.Number.Hex */
c-[mi] { color: #000000 } /* Literal.Number.Integer */
c-[mo] { color: #000000 } /* Literal.Number.Oct */
c-[sb] { color: #a67f59 } /* Literal.String.Backtick */
c-[sc] { color: #a67f59 } /* Literal.String.Char */
c-[sd] { color: #a67f59 } /* Literal.String.Doc */
c-[se] { color: #a67f59 } /* Literal.String.Escape */
c-[sh] { color: #a67f59 } /* Literal.String.Heredoc */
c-[si] { color: #a67f59 } /* Literal.String.Interpol */
c-[sx] { color: #a67f59 } /* Literal.String.Other */
c-[sr] { color: #a67f59 } /* Literal.String.Regex */
c-[ss] { color: #a67f59 } /* Literal.String.Symbol */
c-[vc] { color: #0077aa } /* Name.Variable.Class */
c-[vg] { color: #0077aa } /* Name.Variable.Global */
c-[vi] { color: #0077aa } /* Name.Variable.Instance */
c-[il] { color: #000000 } /* Literal.Number.Integer.Long */
</style>
<style>/* style-darkmode */

@media (prefers-color-scheme: dark) {
    :root {
        --text: #ddd;
        --bg: black;

        --unofficial-watermark: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='400' height='400'%3E%3Cg fill='%23100808' transform='translate(200 200) rotate(-45) translate(-200 -200)' stroke='%23100808' stroke-width='3'%3E%3Ctext x='50%25' y='220' style='font: bold 70px sans-serif; text-anchor: middle; letter-spacing: 6px;'%3EUNOFFICIAL%3C/text%3E%3Ctext x='50%25' y='305' style='font: bold 70px sans-serif; text-anchor: middle; letter-spacing: 6px;'%3EDRAFT%3C/text%3E%3C/g%3E%3C/svg%3E");

        --logo-bg: #1a5e9a;
        --logo-active-bg: #c00;
        --logo-text: white;

        --tocnav-normal-text: #999;
        --tocnav-normal-bg: var(--bg);
        --tocnav-hover-text: var(--tocnav-normal-text);
        --tocnav-hover-bg: #080808;
        --tocnav-active-text: #f44;
        --tocnav-active-bg: var(--tocnav-normal-bg);

        --tocsidebar-text: var(--text);
        --tocsidebar-bg: #080808;
        --tocsidebar-shadow: rgba(255,255,255,.1);
        --tocsidebar-heading-text: hsla(203,20%,40%,.7);

        --toclink-text: var(--text);
        --toclink-underline: #6af;
        --toclink-visited-text: var(--toclink-text);
        --toclink-visited-underline: #054572;

        --heading-text: #8af;

        --hr-text: var(--text);

        --algo-border: #456;

        --del-text: #f44;
        --del-bg: transparent;
        --ins-text: #4a4;
        --ins-bg: transparent;

        --a-normal-text: #6af;
        --a-normal-underline: #555;
        --a-visited-text: var(--a-normal-text);
        --a-visited-underline: var(--a-normal-underline);
        --a-hover-bg: rgba(25%, 25%, 25%, .2);
        --a-active-text: #f44;
        --a-active-underline: var(--a-active-text);

        --borderedblock-bg: rgba(255, 255, 255, .05);

        --blockquote-border: silver;
        --blockquote-bg: var(--borderedblock-bg);
        --blockquote-text: currentcolor;

        --issue-border: #e05252;
        --issue-bg: var(--borderedblock-bg);
        --issue-text: var(--text);
        --issueheading-text: hsl(0deg, 70%, 70%);

        --example-border: hsl(50deg, 90%, 60%);
        --example-bg: var(--borderedblock-bg);
        --example-text: var(--text);
        --exampleheading-text: hsl(50deg, 70%, 70%);

        --note-border: hsl(120deg, 100%, 35%);
        --note-bg: var(--borderedblock-bg);
        --note-text: var(--text);
        --noteheading-text: hsl(120, 70%, 70%);
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   <p data-fill-with="logo"></p>
   <h1 class="p-name no-ref" id="title">P1664R6<br>reconstructible_range - a concept for putting ranges back together</h1>
   <h2 class="no-num no-toc no-ref heading settled" id="profile-and-date"><span class="content">Published Proposal, <time class="dt-updated" datetime="2022-01-03">2022-01-03</time></span></h2>
   <div data-fill-with="spec-metadata">
    <dl>
     <dt class="editor">Authors:
     <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:phdofthehouse@gmail.com">JeanHeyd Meneide</a>
     <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:h2@fsfe.org">Hannes Hauswedell</a>
     <dt>Audience:
     <dd>LEWG
     <dt>Project:
     <dd>ISO/IEC JTC1/SC22/WG21 14882: Programming Language — C++
     <dt>Target:
     <dd>C++23
     <dt>Latest:
     <dd><a href="https://thephd.dev/_vendor/future_cxx/papers/d1664.html">https://thephd.dev/_vendor/future_cxx/papers/d1664.html</a>
    </dl>
   </div>
   <div data-fill-with="warning"></div>
   <hr title="Separator for header">
  </div>
  <div class="p-summary" data-fill-with="abstract">
   <h2 class="no-num no-toc no-ref heading settled" id="abstract"><span class="content">Abstract</span></h2>
   <p>This paper proposes new concepts to the Standard Library for ranges called Reconstructible Ranges for the purpose of ensuring a range/view broken down into its two iterators can be "glued" back together using an ADL-found function taking a tag, the range’s iterator, and the range’s sentinel.</p>
  </div>
  <nav data-fill-with="table-of-contents" id="toc">
   <h2 class="no-num no-toc no-ref" id="contents">Table of Contents</h2>
   <ol class="toc" role="directory">
    <li>
     <a href="#changelog"><span class="secno">1</span> <span class="content">Revision History</span></a>
     <ol class="toc">
      <li><a href="#changelog-r6"><span class="secno">1.1</span> <span class="content">Revision 6 - January 3<sup>rd</sup>, 2022</span></a>
      <li><a href="#changelog-r5"><span class="secno">1.2</span> <span class="content">Revision 5 - August 15<sup>th</sup>, 2021</span></a>
      <li><a href="#changelog-r4"><span class="secno">1.3</span> <span class="content">Revision 4 - June 15<sup>th</sup>, 2021</span></a>
      <li><a href="#changelog-r3"><span class="secno">1.4</span> <span class="content">Revision 3 - April 15<sup>th</sup>, 2021</span></a>
      <li><a href="#changelog-r2"><span class="secno">1.5</span> <span class="content">Revision 2 - January 13<sup>th</sup>, 2020</span></a>
      <li><a href="#changelog-r1"><span class="secno">1.6</span> <span class="content">Revision 1 - November 24<sup>th</sup>, 2019</span></a>
      <li><a href="#changelog-r0"><span class="secno">1.7</span> <span class="content">Revision 0 - August, 5<sup>th</sup>, 2019</span></a>
     </ol>
    <li>
     <a href="#motivation"><span class="secno">2</span> <span class="content">Motivation</span></a>
     <ol class="toc">
      <li><a href="#motivation-origin"><span class="secno">2.1</span> <span class="content">Origin</span></a>
      <li><a href="#motivation-preservation"><span class="secno">2.2</span> <span class="content">Preservation of Properties</span></a>
      <li><a href="#motivation-split"><span class="secno">2.3</span> <span class="content">Superior String Splitting</span></a>
      <li><a href="#motivation-compilation"><span class="secno">2.4</span> <span class="content">Compile-Time and Interoperability</span></a>
     </ol>
    <li>
     <a href="#design"><span class="secno">3</span> <span class="content">Design</span></a>
     <ol class="toc">
      <li><a href="#design-borrowed"><span class="secno">3.1</span> <span class="content">Range? Why not "Borrowed Range"?</span></a>
      <li><a href="#design-multiple"><span class="secno">3.2</span> <span class="content">Multiple, Safe Reconstruction Points</span></a>
      <li><a href="#design-all"><span class="secno">3.3</span> <span class="content">Opt-in?</span></a>
      <li><a href="#design-applicable"><span class="secno">3.4</span> <span class="content">Applicability</span></a>
      <li>
       <a href="#design-overloads"><span class="secno">3.5</span> <span class="content">Why The Overloads?</span></a>
       <ol class="toc">
        <li><a href="#design-overloads-split"><span class="secno">3.5.1</span> <span class="content">Case 0: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>split</c-></code></span></a>
        <li><a href="#design-overloads-max-info"><span class="secno">3.5.2</span> <span class="content">Case 1: <code class="highlight"><c- n>zstring</c-></code> and <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>drop</c-></code></span></a>
        <li><a href="#design-overloads-legacy"><span class="secno">3.5.3</span> <span class="content">Case 2: Legacy Iterator Code</span></a>
        <li><a href="#design-overloads-efficiency"><span class="secno">3.5.4</span> <span class="content">Case 3: <code class="highlight"><c- n>transform_view</c-></code></span></a>
       </ol>
      <li><a href="#design-alternative0"><span class="secno">3.6</span> <span class="content">Alternative Design: <code class="highlight"><c- p>(</c-><c- n>range</c-><c- p>,</c-> <c- n>iterator</c-><c- p>,</c-> <c- n>sentinel</c-><c- p>)</c-></code> Reconstruction Point</span></a>
      <li><a href="#design-containers"><span class="secno">3.7</span> <span class="content">Expanding to Owning Containers and More?</span></a>
     </ol>
    <li><a href="#experience"><span class="secno">4</span> <span class="content">Deployment Experience</span></a>
    <li><a href="#impact"><span class="secno">5</span> <span class="content">Impact</span></a>
    <li>
     <a href="#wording"><span class="secno">6</span> <span class="content">Proposed Changes</span></a>
     <ol class="toc">
      <li><a href="#wording-feature"><span class="secno">6.1</span> <span class="content">Feature Test Macro</span></a>
      <li><a href="#wording-intent"><span class="secno">6.2</span> <span class="content">Intent</span></a>
      <li>
       <a href="#wording-specification"><span class="secno">6.3</span> <span class="content">Proposed Library Wording</span></a>
       <ol class="toc">
        <li><a href="#wording-specification-feature_test"><span class="secno">6.3.1</span> <span class="content">Add a feature test macro <code class="highlight"><c- n>__cpp_lib_reconstructible_range</c-></code>.</span></a>
        <li><a href="#wording-specification-reconstruct_cpo_synopsis"><span class="secno">6.3.2</span> <span class="content">Insert into §24.2 Header <code class="highlight"><c- o>&lt;</c-><c- n>ranges</c-><c- o>></c-></code> Synopsis <span>[ranges.syn</span>] a new customization point object in the inline namespace:</span></a>
        <li><a href="#wording-specification-concepts"><span class="secno">6.3.3</span> <span class="content">Insert into §24.4.2 Ranges <span>[range.range</span>]'s after paragraph 7, one additional paragraph:</span></a>
        <li><a href="#wording-specification-reconstruct_cpo"><span class="secno">6.3.4</span> <span class="content">Insert a new sub-clause "§24.3.13 <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-></code> [<strong>range.prim.recons</strong>]", after "§24.3.12 <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>cdata</c-></code> [<span><b>range.prim.cdata</b></span>]":</span></a>
        <li><a href="#wording-specification-string_view_synopsis"><span class="secno">6.3.5</span> <span class="content">Add to "§21.4.3.1 <code class="highlight"><c- n>General</c-></code>" [<span>string.view.template.general</span>] a <code class="highlight"><c- k>friend</c-></code> function ADL extension point for <code class="highlight"><c- n>basic_string_view</c-></code>:</span></a>
        <li><a href="#wording-specification-string_view"><span class="secno">6.3.6</span> <span class="content">Add a new subclause "§21.4.��� <code class="highlight"><c- n>Range</c-> <c- n>Reconstruction</c-></code>" [string.view.reconstruct] in §21.4:</span></a>
        <li><a href="#wording-specification-span_synopsis"><span class="secno">6.3.7</span> <span class="content">Add to "§22.7.3.1 <code class="highlight"><c- n>Overview</c-></code>" [<span>span.overview</span>] a <code class="highlight"><c- k>friend</c-></code> function ADL extension point for <code class="highlight"><c- n>span</c-></code>:</span></a>
        <li><a href="#wording-specification-span"><span class="secno">6.3.8</span> <span class="content">Add a new subclause "§22.7.3.���� <code class="highlight"><c- n>Range</c-> <c- n>Reconstruction</c-></code>" [span.reconstruct] in §22.7.3:</span></a>
        <li><a href="#wording-specification-subrange_synopsis"><span class="secno">6.3.9</span> <span class="content">Add to "§24.5.4.1 <code class="highlight"><c- n>General</c-></code>" [<span>range.subrange.general</span>] a <code class="highlight"><c- k>friend</c-></code> function ADL extension point for <code class="highlight"><c- n>subrange</c-></code>:</span></a>
        <li><a href="#wording-specification-subrange"><span class="secno">6.3.10</span> <span class="content">Add a new subclause "§24.5.4.���� <code class="highlight"><c- n>Range</c-> <c- n>Reconstruction</c-></code>" [range.subrange.reconstruct] in §24.5.4:</span></a>
        <li><a href="#wording-specification-iota_view_synopsis"><span class="secno">6.3.11</span> <span class="content">Add to "§24.6.4.2 Class template <code class="highlight"><c- n>iota_view</c-></code>" [<span>range.iota</span>] a <code class="highlight"><c- k>friend</c-></code> function ADL extension point for <code class="highlight"><c- n>iota_view</c-></code>:</span></a>
        <li><a href="##wording-specification-iota_view"><span class="secno">6.3.12</span> <span class="content">Add one new paragraph to "§24.6.4.2 Class template <code class="highlight"><c- n>iota_view</c-></code>" [<span>range.iota</span>]:</span></a>
        <li><a href="#wording-specification-empty_view_synopsis"><span class="secno">6.3.13</span> <span class="content">Add to "§24.6.2.2 Class template <code class="highlight"><c- n>empty_view</c-></code>" [<span>range.empty.view</span>] a <code class="highlight"><c- k>friend</c-></code> function ADL extension point for <code class="highlight"><c- n>empty_view</c-></code>:</span></a>
        <li><a href="#wording-specification-transform_view_synopsis"><span class="secno">6.3.14</span> <span class="content">Add to "§24.7.6.2 Class template <code class="highlight"><c- n>transform_view</c-></code>" [<span>range.transform.view</span>] a <code class="highlight"><c- k>friend</c-></code> function ADL extension point for <code class="highlight"><c- n>transform_view</c-></code>:</span></a>
        <li><a href="##wording-specification-transform_view"><span class="secno">6.3.15</span> <span class="content">Add new paragraphs to "§24.6.4.2 Class template <code class="highlight"><c- n>transform_view</c-></code>" [<span>range.transform</span>]:</span></a>
        <li><a href="#wording-specification-views_take"><span class="secno">6.3.16</span> <span class="content">Modify "§24.7.7.1 Overview " [<span>range.take.overview</span>] for <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>take</c-></code>'s paragraph 2:</span></a>
        <li><a href="#wording-specification-views_drop"><span class="secno">6.3.17</span> <span class="content">Modify "§24.7.9.1 Overview " [<span>range.drop.overview</span>] for <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>drop</c-></code>'s paragraph 2:</span></a>
        <li><a href="#wording-specification-views_split_find_next"><span class="secno">6.3.18</span> <span class="content">Modify "§24.7.14.2 Class template <code class="highlight"><c- n>split_</c->­<c- n>view</c-></code>" [<span>range.split.view</span>] for <code class="highlight"><c- n>split_view</c-></code>'s <i><code class="highlight"><c- n>find</c-><c- o>-</c-><c- n>next</c-></code></i> exposition-only function:</span></a>
        <li><a href="#wording-specification-split_iterator_value_type"><span class="secno">6.3.19</span> <span class="content">Modify "§24.7.14.3 Class <code class="highlight"><c- n>split_</c->­<c- n>view</c->​<c- o>::</c->​<c- n>iterator</c-></code>" [<span>range.split.iterator</span>] for <code class="highlight"><c- n>split_view</c-><c- o>&lt;</c->…<c- o>>::</c-><c- n>iterator</c-></code>'s <code class="highlight"><c- n>value_type</c-></code> in the Synopsis:</span></a>
        <li><a href="#wording-specification-views_split"><span class="secno">6.3.20</span> <span class="content">Modify "§24.7.14.2 Class template <code class="highlight"><c- n>split_</c->­<c- n>view</c-></code>" [<span>range.split.view</span>] for <code class="highlight"><c- n>split_view</c-></code>'s Overview and paragraph 5:</span></a>
       </ol>
     </ol>
    <li><a href="#acknowledgements"><span class="secno">7</span> <span class="content">Acknowledgements</span></a>
    <li>
     <a href="#references"><span class="secno"></span> <span class="content">References</span></a>
     <ol class="toc">
      <li><a href="#informative"><span class="secno"></span> <span class="content">Informative References</span></a>
     </ol>
   </ol>
  </nav>
  <main>
   <h2 class="heading settled" data-level="1" id="changelog"><span class="secno">1. </span><span class="content">Revision History</span><a class="self-link" href="#changelog"></a></h2>
   <h3 class="heading settled" data-level="1.1" id="changelog-r6"><span class="secno">1.1. </span><span class="content">Revision 6 - January 3<sup>rd</sup>, 2022</span><a class="self-link" href="#changelog-r6"></a></h3>
   <ul>
    <li data-md>
     <p>Improve the <a href="#motivation">§ 2 Motivation</a> section, including more explanation which relates to <a href="#motivation-split">§ 2.3 Superior String Splitting</a>.</p>
    <li data-md>
     <p>Trim the customization points slightly and improve the motivation for such points.</p>
    <li data-md>
     <p>Add case-by-case justifications for the extension points, shown in the <a href="#design-overloads">§ 3.5 Why The Overloads?</a> section.</p>
    <li data-md>
     <p>Vastly improve the wording, especially for <a href="#wording-specification-views_split_find_next">the new split wording</a>.</p>
    <li data-md>
     <p>Include all feedback from SG9 Ranges December 20<sup>th</sup>, 2021 Virtual Meeting.</p>
   </ul>
   <h3 class="heading settled" data-level="1.2" id="changelog-r5"><span class="secno">1.2. </span><span class="content">Revision 5 - August 15<sup>th</sup>, 2021</span><a class="self-link" href="#changelog-r5"></a></h3>
   <ul>
    <li data-md>
     <p>Vastly improve wording and address e-mail feedback (thanks, Hannes Hauswedell and Barry Revzin).</p>
    <li data-md>
     <p>Use the <code class="highlight"><c- n>is_enum_v</c-></code> and <code class="highlight"><c- n>is_class_v</c-></code> guards to prevent all bad catch-all (thanks, Christopher Di Bella).</p>
    <li data-md>
     <p>At the moment, we cannot have the <i><code class="highlight"><c- n>iterator</c-></code></i> and <i><code class="highlight"><c- n>sentinel</c-></code></i> types for things like <code class="highlight"><c- n>iota_view</c-></code> in the standard-mandated, exposition-only italics, so this little note up here will have to do.</p>
    <li data-md>
     <p>Ensure that the concepts are properly specified.</p>
    <li data-md>
     <p>Add lots more motivation to the design, particularly <a href="#design-overloads">§ 3.5 Why The Overloads?</a>.</p>
   </ul>
   <h3 class="heading settled" data-level="1.3" id="changelog-r4"><span class="secno">1.3. </span><span class="content">Revision 4 - June 15<sup>th</sup>, 2021</span><a class="self-link" href="#changelog-r4"></a></h3>
   <ul>
    <li data-md>
     <p>Rewrite most of the wording.</p>
    <li data-md>
     <p>Fix up the design section to always use an ADL Customization Point, all the time. The <code class="highlight"><c- n>is_class_v</c-></code> and <code class="highlight"><c- n>is_enum_v</c-></code> protects against most bad cases.</p>
   </ul>
   <h3 class="heading settled" data-level="1.4" id="changelog-r3"><span class="secno">1.4. </span><span class="content">Revision 3 - April 15<sup>th</sup>, 2021</span><a class="self-link" href="#changelog-r3"></a></h3>
   <ul>
    <li data-md>
     <p>Vastly improve examples.</p>
    <li data-md>
     <p>Re-target motivation.</p>
    <li data-md>
     <p>Adjust fixes for things that have changed since C++20.</p>
   </ul>
   <h3 class="heading settled" data-level="1.5" id="changelog-r2"><span class="secno">1.5. </span><span class="content">Revision 2 - January 13<sup>th</sup>, 2020</span><a class="self-link" href="#changelog-r2"></a></h3>
   <ul>
    <li data-md>
     <p>Improve wording and add more explanation in the design sections for the changes.</p>
   </ul>
   <h3 class="heading settled" data-level="1.6" id="changelog-r1"><span class="secno">1.6. </span><span class="content">Revision 1 - November 24<sup>th</sup>, 2019</span><a class="self-link" href="#changelog-r1"></a></h3>
   <ul>
    <li data-md>
     <p>Change to <code class="highlight"><c- n>snake_case</c-></code> concepts. (November 6<sup>th</sup>)</p>
    <li data-md>
     <p>Update wording to target <a data-link-type="biblio" href="#biblio-n4835">[n4835]</a>. (November 6<sup>th</sup>)</p>
    <li data-md>
     <p>Moved by LWG! 🎉 (November 6<sup>th</sup>)</p>
    <li data-md>
     <p>Last minute objection to this paper in plenary.</p>
    <li data-md>
     <p>Withdrawn; targeting C++23 instead with better design.</p>
    <li data-md>
     <p>Explored 3 different designs offline: settle on 1 (thanks, Oktal).</p>
   </ul>
   <h3 class="heading settled" data-level="1.7" id="changelog-r0"><span class="secno">1.7. </span><span class="content">Revision 0 - August, 5<sup>th</sup>, 2019</span><a class="self-link" href="#changelog-r0"></a></h3>
   <ul>
    <li data-md>
     <p>Initial release.</p>
   </ul>
   <h2 class="heading settled" data-level="2" id="motivation"><span class="secno">2. </span><span class="content">Motivation</span><a class="self-link" href="#motivation"></a></h2>
   <p>Below is a quick snapshot of the improvements provided by this paper:</p>
   <table>
    <tbody>
     <tr>
      <th>C++20
      <th>With Proposal
     <tr>
      <td>
<pre class="language-cpp highlight"><c- k>template</c-> <c- o>&lt;</c-><c- k>typename</c-> <c- nc>T</c-><c- o>></c->
<c- k>using</c-> <c- n>span</c-> <c- o>=</c-> <c- n>quickcpplib</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>;</c->

<c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-> <c- n>vec</c-><c- p>{</c-><c- mi>1</c-><c- p>,</c-> <c- mi>2</c-><c- p>,</c-> <c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>,</c-> <c- mi>5</c-><c- p>};</c->
<c- n>span</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-> <c- n>s</c-><c- p>{</c-><c- n>vec</c-><c- p>.</c-><c- n>data</c-><c- p>(),</c-> <c- mi>5</c-><c- p>};</c->
<c- n>span</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-> <c- n>v</c-> <c- o>=</c-> <c- n>s</c-> <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>drop</c-><c- p>(</c-><c- mi>1</c-><c- p>)</c-> <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>take</c-><c- p>(</c-><c- mi>10</c-><c- p>)</c->
           <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>drop</c-><c- p>(</c-><c- mi>1</c-><c- p>)</c-> <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>take</c-><c- p>(</c-><c- mi>10</c-><c- p>);</c->
</pre>
       ❌ - Compilation error 
<pre class="language-cpp highlight"><c- k>template</c-> <c- o>&lt;</c-><c- k>typename</c-> <c- nc>T</c-><c- o>></c->
<c- k>using</c-> <c- n>span</c-> <c- o>=</c-> <c- n>quickcpplib</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>;</c->

<c- n>std</c-><c- o>::</c-><c- n>vector</c-> <c- n>vec</c-><c- p>{</c-><c- mi>1</c-><c- p>,</c-> <c- mi>2</c-><c- p>,</c-> <c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>,</c-> <c- mi>5</c-><c- p>};</c->
<c- n>span</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-> <c- n>s</c-><c- p>{</c-><c- n>vec</c-><c- p>.</c-><c- n>data</c-><c- p>(),</c-> <c- mi>5</c-><c- p>};</c->
<c- k>auto</c-> <c- n>v</c-> <c- o>=</c-> <c- n>s</c-> <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>drop</c-><c- p>(</c-><c- mi>1</c-><c- p>)</c-> <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>take</c-><c- p>(</c-><c- mi>10</c-><c- p>)</c->
           <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>drop</c-><c- p>(</c-><c- mi>1</c-><c- p>)</c-> <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>take</c-><c- p>(</c-><c- mi>10</c-><c- p>);</c->
</pre>
       <p>⚠️ - Compiles, but <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>v</c-><c- p>)</c-></code> is <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>take_view</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>drop_view</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>take_view</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>drop_view</c-><c- o>&lt;</c-><c- n>span</c-><c- o>&lt;</c-><c- b>int</c-><c- p>,</c-> <c- n>dynamic_extent</c-><c- o>>>>>></c-></code></p>
      <td>
<pre class="language-cpp highlight"><c- k>template</c-> <c- o>&lt;</c-><c- k>typename</c-> <c- nc>T</c-><c- o>></c->
<c- k>using</c-> <c- n>span</c-> <c- o>=</c-> <c- n>quickcpplib</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>;</c->

<c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-> <c- n>vec</c-><c- p>{</c-><c- mi>1</c-><c- p>,</c-> <c- mi>2</c-><c- p>,</c-> <c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>,</c-> <c- mi>5</c-><c- p>};</c->
<c- n>span</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-> <c- n>s</c-><c- p>{</c-><c- n>vec</c-><c- p>.</c-><c- n>data</c-><c- p>(),</c-> <c- mi>5</c-><c- p>};</c->
<c- n>span</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-> <c- n>v</c-> <c- o>=</c-> <c- n>s</c-> <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>drop</c-><c- p>(</c-><c- mi>1</c-><c- p>)</c-> <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>take</c-><c- p>(</c-><c- mi>10</c-><c- p>)</c->
           <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>drop</c-><c- p>(</c-><c- mi>1</c-><c- p>)</c-> <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>take</c-><c- p>(</c-><c- mi>10</c-><c- p>);</c->
</pre>
       ✔️ - Compiles and works with no extra template instantiations 
<pre class="language-cpp highlight"><c- k>template</c-> <c- o>&lt;</c-><c- k>typename</c-> <c- nc>T</c-><c- o>></c->
<c- k>using</c-> <c- n>span</c-> <c- o>=</c-> <c- n>quickcpplib</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>;</c->

<c- n>std</c-><c- o>::</c-><c- n>vector</c-> <c- n>vec</c-><c- p>{</c-><c- mi>1</c-><c- p>,</c-> <c- mi>2</c-><c- p>,</c-> <c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>,</c-> <c- mi>5</c-><c- p>};</c->
<c- n>span</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-> <c- n>s</c-><c- p>{</c-><c- n>vec</c-><c- p>.</c-><c- n>data</c-><c- p>(),</c-> <c- mi>5</c-><c- p>};</c->
<c- k>auto</c-> <c- n>v</c-> <c- o>=</c-> <c- n>s</c-> <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>drop</c-><c- p>(</c-><c- mi>1</c-><c- p>)</c-> <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>take</c-><c- p>(</c-><c- mi>10</c-><c- p>)</c->
           <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>drop</c-><c- p>(</c-><c- mi>1</c-><c- p>)</c-> <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>take</c-><c- p>(</c-><c- mi>10</c-><c- p>);</c->
</pre>
       <p>✔️ - Compiles and works with no extra templates. <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>v</c-><c- p>)</c-></code> is <code class="highlight"><c- n>quickcpplib</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-></code></p>
     <tr>
      <td>
<pre class="language-cpp highlight"><c- b>char16_t</c-> <c- n>output_buffer</c-><c- p>[</c-><c- mi>432</c-><c- p>];</c->
<c- n>llvm</c-><c- o>::</c-><c- n>StringRef</c-> <c- n>input</c-><c- p>(</c-><c- s>"𐌀𐌖𐌋𐌄𐌑𐌉·𐌌𐌄𐌕𐌄𐌋𐌉𐌑 𐑡𐑹𐑡 ·𐑚𐑻𐑯𐑸𐑛 ·𐑖𐑷"</c-><c- p>);</c->
<c- n>llvm</c-><c- o>::</c-><c- n>MutableArrayRef</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>></c-> <c- n>output</c-><c- p>(</c-><c- n>output_buffer</c-><c- p>,</c-> <c- mi>432</c-><c- p>);</c->

<c- k>auto</c-> <c- n>encoding_result</c-> <c- o>=</c-> <c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>transcode_into</c-><c- p>(</c-><c- n>input</c-><c- p>,</c-> <c- n>output</c->
	<c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>compat_utf8</c-><c- p>,</c-> <c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>utf16</c-><c- p>);</c->
<c- c1>// compiler error here (C++20) !!</c->
<c- n>llvm</c-><c- o>::</c-><c- n>StringRef</c-> <c- n>unprocessed_input</c-> 
	<c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>input</c-><c- p>;</c->
<c- n>llvm</c-><c- o>::</c-><c- n>MutableArrayRef</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>></c-> <c- n>unconsumed_output</c-> 
	<c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>output</c-><c- p>;</c->
</pre>
       ❌ - Compilation error 
<pre class="language-cpp highlight"><c- n>std</c-><c- o>::</c-><c- n>u8string</c-> <c- n>name</c-> <c- o>=</c-> <c- s>"𐌀𐌖𐌋𐌄𐌑𐌉·𐌌𐌄𐌕𐌄𐌋𐌉𐌑 𐑡𐑹𐑡 ·𐑚𐑻𐑯𐑸𐑛 ·𐑖𐑷"</c-><c- p>;</c->
<c- b>char16_t</c-> <c- n>conversion_buffer</c-><c- p>[</c-><c- mi>432</c-><c- p>];</c->
<c- n>std</c-><c- o>::</c-><c- n>u8string_view</c-> <c- n>input</c-><c- p>(</c-><c- n>name</c-><c- p>);</c->
<c- n>std</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>></c-> <c- n>output</c-><c- p>(</c-><c- n>conversion_buffer</c-><c- p>,</c-> <c- mi>432</c-><c- p>);</c->

<c- k>auto</c-> <c- n>encoding_result</c-> <c- o>=</c-> <c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>transcode_into</c-><c- p>(</c-><c- n>input</c-><c- p>,</c-> <c- n>output</c-><c- p>,</c->
	<c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>compat_utf8</c-><c- p>,</c-> <c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>utf16</c-><c- p>);</c->
<c- k>auto</c-> <c- n>unprocessed_input</c-> <c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>input</c-><c- p>;</c->
<c- k>auto</c-> <c- n>unconsumed_output</c-> <c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>output</c-><c- p>;</c->
</pre>
       ⚠️ - Compiles, but <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>unprocessed_input</c-><c- p>)</c-></code> is <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>u8string_view</c-><c- o>::</c-><c- n>iterator</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>u8string_view</c-><c- o>::</c-><c- n>iterator</c-><c- o>></c-></code> and <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>unconsumed_output</c-><c- p>)</c-></code> is <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- n>llvm</c-><c- o>::</c-><c- n>MutableArrayRef</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>>::</c-><c- n>iterator</c-><c- p>,</c-> <c- n>llvm</c-><c- o>::</c-><c- n>MutableArrayRef</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>>::</c-><c- n>iterator</c-><c- o>></c-></code> 
      <td>
<pre class="language-cpp highlight"><c- b>char16_t</c-> <c- n>output_buffer</c-><c- p>[</c-><c- mi>432</c-><c- p>];</c->
<c- n>llvm</c-><c- o>::</c-><c- n>StringRef</c-> <c- n>input</c-><c- p>(</c-><c- s>"𐌀𐌖𐌋𐌄𐌑𐌉·𐌌𐌄𐌕𐌄𐌋𐌉𐌑 𐑡𐑹𐑡 ·𐑚𐑻𐑯𐑸𐑛 ·𐑖𐑷"</c-><c- p>);</c->
<c- n>llvm</c-><c- o>::</c-><c- n>MutableArrayRef</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>></c-> <c- n>output</c-><c- p>(</c-><c- n>output_buffer</c-><c- p>,</c-> <c- mi>432</c-><c- p>);</c->

<c- k>auto</c-> <c- n>encoding_result</c-> <c- o>=</c-> <c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>transcode_into</c-><c- p>(</c-><c- n>input</c-><c- p>,</c-> <c- n>output</c-><c- p>,</c->
	<c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>utf8</c-><c- p>,</c-> <c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>utf16</c-><c- p>);</c->

<c- n>llvm</c-><c- o>::</c-><c- n>StringRef</c-> <c- n>unprocessed_input</c-> 
	<c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>input</c-><c- p>;</c->
<c- n>llvm</c-><c- o>::</c-><c- n>MutableArrayRef</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>></c-> <c- n>unconsumed_output</c-> 
	<c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>output</c-><c- p>;</c->
</pre>
       ✔️ - Compiles and works, types match input. 
<pre class="language-cpp highlight"><c- n>std</c-><c- o>::</c-><c- n>u8string</c-> <c- n>name</c-> <c- o>=</c-> <c- s>"𐌀𐌖𐌋𐌄𐌑𐌉·𐌌𐌄𐌕𐌄𐌋𐌉𐌑 𐑡𐑹𐑡 ·𐑚𐑻𐑯𐑸𐑛 ·𐑖𐑷"</c-><c- p>;</c->
<c- b>char16_t</c-> <c- n>conversion_buffer</c-><c- p>[</c-><c- mi>432</c-><c- p>];</c->
<c- n>std</c-><c- o>::</c-><c- n>u8string_view</c-> <c- n>input</c-><c- p>(</c-><c- n>name</c-><c- p>);</c->
<c- n>std</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>></c-> <c- n>output</c-><c- p>(</c-><c- n>conversion_buffer</c-><c- p>,</c-> <c- mi>432</c-><c- p>);</c->

<c- k>auto</c-> <c- n>encoding_result</c-> <c- o>=</c-> <c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>transcode_into</c-><c- p>(</c-><c- n>input</c-><c- p>,</c-> <c- n>output</c-><c- p>,</c->
	<c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>utf8</c-><c- p>,</c-> <c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>utf16</c-><c- p>);</c->
<c- k>auto</c-> <c- n>unprocessed_input</c-> <c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>input</c-><c- p>;</c->
<c- k>auto</c-> <c- n>unconsumed_output</c-> <c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>output</c-><c- p>;</c->
</pre>
       ✔️ - Compiles and works, where <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>unprocessed_input</c-><c- p>)</c-></code> is <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>u8string_view</c-></code> and <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>unconsumed_output</c-><c- p>)</c-></code> is <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>></c-></code>. 
     <tr>
      <td>
<pre class="language-cpp highlight"><c- b>char</c-> <c- k>const</c-><c- o>*</c-> <c- n>words</c-> <c- o>=</c-> <c- s>"A quick brown fox"</c-><c- p>;</c->
<c- k>for</c-> <c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>span</c-> <c- nl>ss</c-> <c- p>:</c-> <c- n>zstring</c-><c- p>{</c-><c- n>words</c-><c- p>}</c-> <c- o>|</c-> <c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>split</c-><c- p>(</c-><c- sc>' '</c-><c- p>))</c-> <c- p>{</c->
    <c- k>auto</c-> <c- n>sv</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>string_view</c-><c- p>(</c-><c- n>ss</c-><c- p>.</c-><c- n>data</c-><c- p>(),</c-> <c- n>ss</c-><c- p>.</c-><c- n>size</c-><c- p>());</c->
    <c- n>std</c-><c- o>::</c-><c- n>cout</c-> <c- o>&lt;&lt;</c-> <c- n>sv</c-> <c- o>&lt;&lt;</c-> <c- sc>'\n'</c-><c- p>;</c->
<c- p>}</c->
</pre>
       ❌ - Compilation error 
<pre class="language-cpp highlight"><c- n>std</c-><c- o>::</c-><c- n>u8string</c-> <c- n>name</c-> <c- o>=</c-> <c- s>"𐌀𐌖𐌋𐌄𐌑𐌉·𐌌𐌄𐌕𐌄𐌋𐌉𐌑 𐑡𐑹𐑡 ·𐑚𐑻𐑯𐑸𐑛 ·𐑖𐑷"</c-><c- p>;</c->
<c- b>char16_t</c-> <c- n>conversion_buffer</c-><c- p>[</c-><c- mi>432</c-><c- p>];</c->
<c- n>std</c-><c- o>::</c-><c- n>u8string_view</c-> <c- n>input</c-><c- p>(</c-><c- n>name</c-><c- p>);</c->
<c- n>std</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>></c-> <c- n>output</c-><c- p>(</c-><c- n>conversion_buffer</c-><c- p>,</c-> <c- mi>432</c-><c- p>);</c->

<c- k>auto</c-> <c- n>encoding_result</c-> <c- o>=</c-> <c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>transcode_into</c-><c- p>(</c-><c- n>input</c-><c- p>,</c-> <c- n>output</c-><c- p>,</c->
	<c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>compat_utf8</c-><c- p>,</c-> <c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>utf16</c-><c- p>);</c->
<c- k>auto</c-> <c- n>unprocessed_input</c-> <c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>input</c-><c- p>;</c->
<c- k>auto</c-> <c- n>unconsumed_output</c-> <c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>output</c-><c- p>;</c->
</pre>
       ⚠️ - Compiles, but <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>unprocessed_input</c-><c- p>)</c-></code> is <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>u8string_view</c-><c- o>::</c-><c- n>iterator</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>u8string_view</c-><c- o>::</c-><c- n>iterator</c-><c- o>></c-></code> and <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>unconsumed_output</c-><c- p>)</c-></code> is <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- n>llvm</c-><c- o>::</c-><c- n>MutableArrayRef</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>>::</c-><c- n>iterator</c-><c- p>,</c-> <c- n>llvm</c-><c- o>::</c-><c- n>MutableArrayRef</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>>::</c-><c- n>iterator</c-><c- o>></c-></code> 
      <td>
<pre class="language-cpp highlight"><c- b>char16_t</c-> <c- n>output_buffer</c-><c- p>[</c-><c- mi>432</c-><c- p>];</c->
<c- n>llvm</c-><c- o>::</c-><c- n>StringRef</c-> <c- n>input</c-><c- p>(</c-><c- s>"𐌀𐌖𐌋𐌄𐌑𐌉·𐌌𐌄𐌕𐌄𐌋𐌉𐌑 𐑡𐑹𐑡 ·𐑚𐑻𐑯𐑸𐑛 ·𐑖𐑷"</c-><c- p>);</c->
<c- n>llvm</c-><c- o>::</c-><c- n>MutableArrayRef</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>></c-> <c- n>output</c-><c- p>(</c-><c- n>output_buffer</c-><c- p>,</c-> <c- mi>432</c-><c- p>);</c->

<c- k>auto</c-> <c- n>encoding_result</c-> <c- o>=</c-> <c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>transcode_into</c-><c- p>(</c-><c- n>input</c-><c- p>,</c-> <c- n>output</c-><c- p>,</c->
	<c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>utf8</c-><c- p>,</c-> <c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>utf16</c-><c- p>);</c->

<c- n>llvm</c-><c- o>::</c-><c- n>StringRef</c-> <c- n>unprocessed_input</c-> 
	<c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>input</c-><c- p>;</c->
<c- n>llvm</c-><c- o>::</c-><c- n>MutableArrayRef</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>></c-> <c- n>unconsumed_output</c-> 
	<c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>output</c-><c- p>;</c->
</pre>
       ✔️ - Compiles and works, types match input. 
<pre class="language-cpp highlight"><c- n>std</c-><c- o>::</c-><c- n>u8string</c-> <c- n>name</c-> <c- o>=</c-> <c- s>"𐌀𐌖𐌋𐌄𐌑𐌉·𐌌𐌄𐌕𐌄𐌋𐌉𐌑 𐑡𐑹𐑡 ·𐑚𐑻𐑯𐑸𐑛 ·𐑖𐑷"</c-><c- p>;</c->
<c- b>char16_t</c-> <c- n>conversion_buffer</c-><c- p>[</c-><c- mi>432</c-><c- p>];</c->
<c- n>std</c-><c- o>::</c-><c- n>u8string_view</c-> <c- n>input</c-><c- p>(</c-><c- n>name</c-><c- p>);</c->
<c- n>std</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>></c-> <c- n>output</c-><c- p>(</c-><c- n>conversion_buffer</c-><c- p>,</c-> <c- mi>432</c-><c- p>);</c->

<c- k>auto</c-> <c- n>encoding_result</c-> <c- o>=</c-> <c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>transcode_into</c-><c- p>(</c-><c- n>input</c-><c- p>,</c-> <c- n>output</c-><c- p>,</c->
	<c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>utf8</c-><c- p>,</c-> <c- n>ztd</c-><c- o>::</c-><c- n>text</c-><c- o>::</c-><c- n>utf16</c-><c- p>);</c->
<c- k>auto</c-> <c- n>unprocessed_input</c-> <c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>input</c-><c- p>;</c->
<c- k>auto</c-> <c- n>unconsumed_output</c-> <c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>output</c-><c- p>;</c->
</pre>
       ✔️ - Compiles and works, where <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>unprocessed_input</c-><c- p>)</c-></code> is <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>u8string_view</c-></code> and <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>unconsumed_output</c-><c- p>)</c-></code> is <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- o>></c-></code>. 
     <tr>
      <td>
<pre class="language-cpp highlight"><c- n>std</c-><c- o>::</c-><c- n>string_view</c-> <c- n>s</c-> <c- o>=</c-> <c- s>"12.22.32.41"</c-><c- p>;</c->

<c- k>auto</c-> <c- n>ints</c-> <c- o>=</c->
	<c- n>s</c-> <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>split</c-><c- p>(</c-><c- sc>'.'</c-><c- p>)</c->
	  <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>transform</c-><c- p>([](</c-><c- k>auto</c-> <c- n>v</c-><c- p>){</c->
		<c- b>int</c-> <c- n>i</c-> <c- o>=</c-> <c- mi>0</c-><c- p>;</c->
		<c- c1>// only the numbers ending in 2</c->
		<c- k>if</c-> <c- p>(</c-><c- n>v</c-><c- p>.</c-><c- n>ends_with</c-><c- p>(</c-><c- sc>'2'</c-><c- p>))</c-> <c- p>{</c->
			<c- n>std</c-><c- o>::</c-><c- n>from_chars</c-><c- p>(</c-><c- n>v</c-><c- p>.</c-><c- n>data</c-><c- p>(),</c-> <c- n>v</c-><c- p>.</c-><c- n>size</c-><c- p>(),</c-> <c- o>&amp;</c-><c- n>i</c-><c- p>);</c->
		<c- p>}</c->
		<c- k>return</c-> <c- n>i</c-><c- p>;</c->
	<c- p>});</c->
</pre>
       ❌ - Compilation error (<code class="highlight"><c- p>.</c-><c- n>starts_with</c-><c- p>(...)</c-></code> is not present on <code class="highlight"><c- n>v</c-></code> which is an object of type <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- k>const</c-> <c- b>char</c-><c- o>*</c-><c- p>,</c-> <c- k>const</c-> <c- b>char</c-><c- o>*</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange_kind</c-><c- o>::</c-><c- n>sized</c-><c- o>></c-></code>). 
      <td>
<pre class="language-cpp highlight"><c- n>std</c-><c- o>::</c-><c- n>string_view</c-> <c- n>s</c-> <c- o>=</c-> <c- s>"12.22.32.41"</c-><c- p>;</c->

<c- k>auto</c-> <c- n>ints</c-> <c- o>=</c->
	<c- n>s</c-> <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>split</c-><c- p>(</c-><c- sc>'.'</c-><c- p>)</c->
	  <c- o>|</c-> <c- n>views</c-><c- o>::</c-><c- n>transform</c-><c- p>([](</c-><c- k>auto</c-> <c- n>v</c-><c- p>){</c->
		<c- b>int</c-> <c- n>i</c-> <c- o>=</c-> <c- mi>0</c-><c- p>;</c->
		<c- c1>// only the numbers ending in 2</c->
		<c- k>if</c-> <c- p>(</c-><c- n>v</c-><c- p>.</c-><c- n>ends_with</c-><c- p>(</c-><c- sc>'2'</c-><c- p>))</c-> <c- p>{</c->
			<c- n>std</c-><c- o>::</c-><c- n>from_chars</c-><c- p>(</c-><c- n>v</c-><c- p>.</c-><c- n>data</c-><c- p>(),</c-> <c- n>v</c-><c- p>.</c-><c- n>size</c-><c- p>(),</c-> <c- o>&amp;</c-><c- n>i</c-><c- p>);</c->
		<c- p>}</c->
		<c- k>return</c-> <c- n>i</c-><c- p>;</c->
	<c- p>});</c->
</pre>
       ✔️ - Compiles and works, as expected (<code class="highlight"><c- n>v</c-></code> is an object of type <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string_view</c-></code>). 
   </table>
   <h3 class="heading settled" data-level="2.1" id="motivation-origin"><span class="secno">2.1. </span><span class="content">Origin</span><a class="self-link" href="#motivation-origin"></a></h3>
   <p>This paper originally began as an attempt to handle the fact that certain views/ranges, once pulled apart into their iterator/sentinel, could not be put back together in any logically consistent manner. Currently in C++, there is no Generic ("with a capital G") way to take a range apart with its iterators and put it back together. That is, the following code is not guaranteed to work:</p>
<pre class="language-cpp highlight"><c- k>template</c-> <c- o>&lt;</c-><c- k>typename</c-> <c- nc>Range</c-><c- o>></c->
<c- k>auto</c-> <c- n>operate_on_and_return_updated_range</c-> <c- p>(</c-><c- n>Range</c-><c- o>&amp;&amp;</c-> <c- n>range</c-><c- p>)</c-> <c- p>{</c->
	<c- k>using</c-> <c- n>I</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>Range</c-><c- o>></c-><c- p>;</c->
	<c- k>using</c-> <c- n>S</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>sentinel_t</c-><c- o>&lt;</c-><c- n>Range</c-><c- o>></c-><c- p>;</c->
	<c- k>using</c-> <c- n>Result</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>Range</c-><c- o>></c->
	<c- k>if</c-> <c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>empty</c-><c- p>(</c-><c- n>range</c-><c- p>))</c-> <c- p>{</c->
		<c- c1>// ⛔!</c->
		<c- c1>// ... the below errors</c->
		<c- k>return</c-> <c- nf>Result</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Range</c-><c- o>></c-><c- p>(</c-><c- n>range</c-><c- p>));</c->
	<c- p>}</c->
	<c- d>/* perform some work with the</c->
<c- d>	iterators or similar */</c->
	<c- k>auto</c-> <c- n>first</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>range</c-><c- p>);</c->
	<c- k>auto</c-> <c- n>last</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>range</c-><c- p>);</c->
	<c- k>if</c-> <c- p>(</c-><c- o>*</c-><c- n>first</c-> <c- o>==</c-> <c- n>u</c->'\<c- mh>0xEF</c->'<c- p>)</c-> <c- p>{</c->
		<c- c1>// ...</c->
		<c- n>std</c-><c- o>::</c-><c- n>advance</c-><c- p>(</c-><c- n>first</c-><c- p>,</c-> <c- mi>3</c-><c- p>);</c->
		<c- c1>// ...</c->
	<c- p>}</c->
	<c- c1>// ... algorithm finished,</c->
	<c- c1>// return the "updated" range!</c->

	<c- c1>// ⛔!</c->
	<c- c1>// ... but the below errors</c->
	<c- k>return</c-> <c- n>Result</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>first</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>last</c-><c- p>));</c->
<c- p>}</c->

<c- b>int</c-> <c- n>main</c-> <c- p>()</c-> <c- p>{</c->
	<c- n>std</c-><c- o>::</c-><c- n>string_view</c-> <c- n>meow_view</c-> <c- o>=</c-> <c- s>"나는 유리를 먹을 수 있어요. 그래도 아프지 않아요"</c-><c- p>;</c->
	<c- c1>// this line will error in C++17 and C++20, or in compatibility</c->
	<c- c1>// libraries</c->
	<c- n>std</c-><c- o>::</c-><c- n>string_view</c-> <c- n>sub_view</c->
		<c- o>=</c-> <c- n>operate_on_and_return_updated_range</c-><c- p>(</c-><c- n>meow_view</c-><c- p>);</c->
	<c- k>return</c-> <c- mi>0</c-><c- p>;</c->
<c- p>}</c->
</pre>
   <p>While all of the container types and a decent chunk of current-day views have constructors that take <code class="highlight"><c- n>iterator</c-><c- p>,</c-> <c- n>iterator</c-></code> pairs or something convertible from those, it was never actually a formal concept. It was recommended to find a better <a data-link-type="biblio" href="#biblio-range-v3-1192">concept to model this property</a>. In the meantime, the current fix is to employ <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>S</c-><c- p>,</c-> <c- n>K</c-><c- o>></c-></code> to return a generic subrange:</p>
<pre class="language-cpp highlight"><c- k>template</c-> <c- o>&lt;</c-><c- k>typename</c-> <c- nc>Range</c-><c- o>></c->
<c- k>auto</c-> <c- n>operate_on_and_return_updated_range</c-> <c- p>(</c-><c- n>Range</c-><c- o>&amp;&amp;</c-> <c- n>range</c-><c- p>)</c-> <c- p>{</c->
	<c- k>using</c-> <c- n>I</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>Range</c-><c- o>></c-><c- p>;</c->
	<c- k>using</c-> <c- n>S</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>sentinel_t</c-><c- o>&lt;</c-><c- n>Range</c-><c- o>></c-><c- p>;</c->
	<c- k>using</c-> <c- n>Result</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>S</c-><c- o>></c-><c- p>;</c->
	<c- k>if</c-> <c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>empty</c-><c- p>(</c-><c- n>range</c-><c- p>))</c-> <c- p>{</c->
		<c- k>return</c-> <c- nf>Result</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Range</c-><c- o>></c-><c- p>(</c-><c- n>range</c-><c- p>));</c->
	<c- p>}</c->
	<c- c1>// perform some work with the</c->
	<c- c1>// iterators or similar</c->
	<c- k>auto</c-> <c- n>first</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>range</c-><c- p>);</c->
	<c- k>auto</c-> <c- n>last</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>range</c-><c- p>);</c->
	<c- k>if</c-> <c- p>(</c-><c- o>*</c-><c- n>first</c-> <c- o>==</c-> <c- n>u</c->'\<c- mh>0xEF</c->'<c- p>)</c-> <c- p>{</c->
		<c- c1>// ...</c->
		<c- n>std</c-><c- o>::</c-><c- n>advance</c-><c- p>(</c-><c- n>first</c-><c- p>,</c-> <c- mi>3</c-><c- p>);</c->
		<c- c1>// ...</c->
	<c- p>}</c->
	<c- c1>// ... algorithm finished,</c->
	<c- c1>// return the "updated" range!</c->

	<c- c1>// now it works!</c->
	<c- k>return</c-> <c- n>Result</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>first</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>last</c-><c- p>));</c->
<c- p>}</c->

<c- b>int</c-> <c- n>main</c-> <c- p>()</c-> <c- p>{</c->
	<c- n>std</c-><c- o>::</c-><c- n>string_view</c-> <c- n>meow_view</c-> <c- o>=</c-> <c- s>"나는 유리를 먹을 수 있어요. 그래도 아프지 않아요"</c-><c- p>;</c->
	<c- k>auto</c-> <c- n>sub_view</c->
		<c- o>=</c-> <c- n>operate_on_and_return_updated_range</c-><c- p>(</c-><c- n>meow_view</c-><c- p>);</c->
	<c- c1>// decltype(sub_view) ==</c->
	<c- c1>//   std::ranges::subrange&lt;std::string_view::iterator,std::string_view::iterator></c->
	<c- c1>//   which is nowhere close to ideal.</c->
	<c- k>return</c-> <c- mi>0</c-><c- p>;</c->
<c- p>}</c->
</pre>
   <p>This makes it work with any two pair of iterators, but quickly becomes undesirable from an interface point of view. If a user passes in a <code class="highlight"><c- n>quickcpplib</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Extent</c-><c- o>></c-></code> or a <code class="highlight"><c- n>llvm</c-><c- o>::</c-><c- n>StringRef</c-></code> that interface and information is entirely lost to the user of the above function. <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- n>Iterator</c-><c- p>,</c-> <c- n>Sentinel</c-><c- p>,</c-> <c- n>Kind</c-><c- o>></c-></code> does not -- and cannot/should not -- mimic the interface of the view it was created from other than what information comes from its iterators: it is the barebones idea of a pair-of-iterators/iterator-sentinel style of range. This is useful in the generic sense that if a library developer must work with iterators, they can always rely on creation of a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-></code> of the iterator and sentinel.</p>
   <h3 class="heading settled" data-level="2.2" id="motivation-preservation"><span class="secno">2.2. </span><span class="content">Preservation of Properties</span><a class="self-link" href="#motivation-preservation"></a></h3>
   <p>Unfortunately, always using <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-></code> decreases usability for end users. Users who have, for example a <code class="highlight"><c- n>llvm</c-><c- o>::</c-><c- n>StringRef</c-></code>, would prefer to have the same type after calling an algorithm. These types have functions and code that are purpose-made for <code class="highlight"><c- n>string_view</c-></code>-like code: losing that intent means needing to reconstruct that from the ground up all over again. There is little reason why the original type needs to be discarded if it supports being put back together from its iterators.</p>
   <p>The break-it-apart-and-then-generic-<code class="highlight"><c- n>subrange</c-></code> approach also discards any range-specific storage optimizations and layout considerations, leaving us with the most bland kind of range similar to the "pair of iterators" model. Consider, for example, <code class="highlight"><c- n>llfio</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code>. The author of the Low Level File IO (LLFIO) library, Niall Douglass, has spent countless days submitting pull requests and change requests to MSVC, GCC, and Clang’s standard libraries to ask them to change their structural layout to match things like the <code class="highlight"><c- n>iovec</c-></code> of their platform or their asynchronous buffer span types. This optimization matters because it realizes the performance difference between having to individually transformed a container of <code class="highlight"><c- n>span</c-></code>s to a more suitable type, or being able to simply <code class="highlight"><c- n>memcpy</c-></code> the desired sequences of spans into the underlying asynchronous operations. If range operations were to be performed on the <code class="highlight"><c- n>llfio</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> type, a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-></code> would hold, in most cases, two iterators rather than an iterator and a size. This completely eliminates the <code class="highlight"><c- n>memcpy</c-></code> optimization. This is not the only place this happens, however: other types have different storages requirements that are not appropriately captured by their iterators in the most general sense, but may benefit from reconstruction and desired type information for the target range they should be constructed into.</p>
   <h3 class="heading settled" data-level="2.3" id="motivation-split"><span class="secno">2.3. </span><span class="content">Superior String Splitting</span><a class="self-link" href="#motivation-split"></a></h3>
   <p><a data-link-type="biblio" href="#biblio-p2210r2">Superior String Splitting</a> is a paper for having both an eager and a lazy split view in the standard library. It argues that because we have a maximally lazy split and always present a forward-range, we should separate the always-input-range functionality of the current split into <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>lazy_split</c-><c- o>*</c-></code> by renaming, and then add more-eager <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>split</c-></code> that takes advantage of the forward-only semantics to upgrade the capabilities of the type and always return a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c-></code>.</p>
   <p>One of the questions it brings up is notable:</p>
   <blockquote>
    <p>For splitting a string, this means we get a range of <code class="highlight"><c- n>subrange</c-><c- o>&lt;</c-><c- n>string</c-><c- o>::</c-><c- n>iterator</c-><c- o>></c-></code> where we might wish we got a <code class="highlight"><c- n>span</c-><c- o>&lt;</c-><c- b>char</c-> <c- k>const</c-><c- o>></c-></code> or a <code class="highlight"><c- n>string_view</c-></code>, but <code class="highlight"><c- n>span</c-><c- o>&lt;</c-><c- b>char</c-> <c- k>const</c-><c- o>></c-></code> is already constructible from <code class="highlight"><c- n>subrange</c-><c- o>&lt;</c-><c- n>string</c-><c- o>::</c-><c- n>iterator</c-><c- o>></c-></code> and string_view would be with the adoption of <a data-link-type="biblio" href="#biblio-p1989r0">[P1989R0]</a>.</p>
    <p>We could additionally favor the char case (since, again, splitting strings is the overwhemlingly common case)…</p>
    <p>… But this just seems weirdly specific and not a good idea.</p>
    <p>— Barry Revzin, <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2210r2.html#what-should-the-reference-type-of-this-be">p2210r2 "§3.1 What should the reference type be?"</a></p>
   </blockquote>
   <p>Revzin notes that string splitting here could return something better than a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- nl>ranges</c-><c- p>:</c-><c- n>subrange</c-></code> based on the input. However, such a proposition in the current C++20 landscape is tenuous at best because it would require adding special cases to the split requirements. The below design comes as a generic way to provide "a reconstructed or related range if possible, otherwise a <code class="highlight"><c- n>subrange</c-></code>". This would meet the requirements of Superior String Splitting while allowing for better return types when an <code class="highlight"><c- n>llvm</c-><c- o>::</c-><c- n>StringRef</c-></code>, <code class="highlight"><c- n>llvm</c-><c- o>::</c-><c- n>ArrayRef</c-></code>, <code class="highlight"><c- n>TArrayView</c-></code> from Unreal Engine, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>wstring_view</c-></code>, or <code class="highlight"><c- n>quickcpplib</c-><c- o>::</c-><c- n>span</c-></code> is used as the input range.</p>
   <h3 class="heading settled" data-level="2.4" id="motivation-compilation"><span class="secno">2.4. </span><span class="content">Compile-Time and Interoperability</span><a class="self-link" href="#motivation-compilation"></a></h3>
   <p>Compilation time goes up as well in the current paradigm. Users must spawn a fresh <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- n>I</c-><c- p>,</c-> <c- n>S</c-><c- p>,</c-> <c- n>K</c-><c- o>></c-></code> for every different set of iterator/sentinel/kind triplet, or handle deeply nested templates in templates as the input types. This makes it impossible to compile interfaces as dynamic libraries without having to explicitly materialize or manually cajole a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-></code> into something more palatable for the regular world.</p>
   <p>There is also a problem where there are a wide variety of ranges that could conceivably meet this criterion, but do not. The author of this paper was not the only one to see utility for this. <a data-link-type="biblio" href="#biblio-p1739r4">[p1739r4]</a> does much the same that this paper does, without the introduction of a concept to formalize the behavior it presents. In particular, it selects views which can realistically have their return types changed to match the input range and operations being performed (or a similarly powerful alternative) by asking whether they can be called with a function called <code class="highlight"><c- n>reconstruct</c-></code> from a subrange of the iterators with the expressions acted upon.</p>
   <ul>
    <li data-md>
     <p>Ranges should be reconstructible from their iterators where applicable;</p>
    <li data-md>
     <p>and, reconstructible ranges serve a useful purpose in generic algorithms, including not losing information and returning it in a much more cromulent and desirable form.</p>
   </ul>
   <p>Therefore, this paper formalizes that concept and provides an <strong>opt-in, user-overridable way</strong> to return a related "reconstructed" type from an tag, an iterator, and a sentinel (or more/less, depending on the necessary situation).</p>
   <h2 class="heading settled" data-level="3" id="design"><span class="secno">3. </span><span class="content">Design</span><a class="self-link" href="#design"></a></h2>
   <p>The design is given in 3 concepts added to the standard:</p>
<pre class="language-cpp highlight"><c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>It</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Sen</c-> <c- o>=</c-> <c- n>It</c-><c- o>></c->
<c- k>concept</c-> <c- nc>iterator_reconstructible_range</c-> <c- o>=</c->
<c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>is_class_v</c-><c- o>&lt;</c-><c- n>It</c-><c- o>></c-> <c- o>||</c-> <c- n>std</c-><c- o>::</c-><c- n>is_class_v</c-><c- o>&lt;</c-><c- n>Sen</c-><c- o>></c-> <c- o>||</c-> <c- n>std</c-><c- o>::</c-><c- n>is_enum_v</c-><c- o>&lt;</c-><c- n>It</c-><c- o>></c-> <c- o>||</c-> <c- n>std</c-><c- o>::</c-><c- n>is_enum_v</c-><c- o>&lt;</c-><c- n>Sen</c-><c- o>></c-><c- p>)</c->
<c- o>&amp;&amp;</c-> <c- k>requires</c-> <c- p>(</c-><c- n>It</c-> <c- n>first</c-><c- p>,</c-> <c- n>Sen</c-> <c- n>last</c-><c- p>)</c-> <c- p>{</c->
	<c- n>reconstruct</c-><c- p>(</c->
		<c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>It</c-><c- o>></c-><c- p>(</c-><c- n>first</c-><c- p>),</c->
		<c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Sen</c-><c- o>></c-><c- p>(</c-><c- n>last</c-><c- p>)</c->
	<c- p>);</c->
<c- p>};</c->

<c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>R</c-><c- p>,</c->
	<c- k>class</c-> <c- nc>It</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c->
	<c- k>class</c-> <c- nc>Sen</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>sentinel_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></c->
<c- k>concept</c-> <c- nc>reconstructible_range</c-> <c- o>=</c->
<c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>range</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c->
<c- o>&amp;&amp;</c-> <c- p>(</c-><c- n>iterator_reconstructible_range</c-><c- o>&lt;</c-><c- n>It</c-><c- p>,</c-> <c- n>Sen</c-><c- o>></c->
<c- o>||</c-> <c- k>requires</c-> <c- p>(</c-><c- n>It</c-> <c- n>first</c-><c- p>,</c-> <c- n>Sen</c-> <c- n>last</c-><c- p>)</c-> <c- p>{</c->
	<c- n>reconstruct</c-><c- p>(</c->
		<c- n>in_place_type</c-><c- o>&lt;</c-><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></c-><c- p>,</c->
		<c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>It</c-><c- o>></c-><c- p>(</c-><c- n>first</c-><c- p>),</c->
		<c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Sen</c-><c- o>></c-><c- p>(</c-><c- n>last</c-><c- p>)</c->
	<c- p>);</c->
<c- p>});</c->

<c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>R</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Tag</c-> <c- o>=</c-> <c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c->
	<c- k>class</c-> <c- nc>It</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c->
	<c- k>class</c-> <c- nc>Sen</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>sentinel_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></c->
<c- k>concept</c-> <c- nc>range_iterator_reconstructible_range</c-> <c- o>=</c->
<c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>range</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c->
<c- o>&amp;&amp;</c-> <c- p>(</c-><c- n>reconstructible_range</c-><c- o>&lt;</c-><c- n>Tag</c-><c- p>,</c-> <c- n>It</c-><c- p>,</c-> <c- n>Sen</c-><c- o>></c->
<c- o>||</c-> <c- k>requires</c-> <c- p>(</c-><c- n>R</c-> <c- n>range</c-><c- p>,</c-> <c- n>It</c-> <c- n>first</c-><c- p>,</c-> <c- n>Sen</c-> <c- n>last</c-><c- p>)</c-> <c- p>{</c->
	<c- n>reconstruct</c-><c- p>(</c->
		<c- n>in_place_type</c-><c- o>&lt;</c-><c- n>Tag</c-><c- o>></c-><c- p>,</c->
		<c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>(</c-><c- n>range</c-><c- p>),</c->
		<c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>It</c-><c- o>></c-><c- p>(</c-><c- n>first</c-><c- p>),</c->
		<c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- n>Sen</c-><c- o>></c-><c- p>(</c-><c- n>last</c-><c- p>)</c->
	<c- p>);</c->
<c- p>});</c->
</pre>
   <p>It is the formalization that a range can be reconstructed from its necessary components. The concepts are a means of implementing the desired Customization Point Object (CPO) which will be called <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-></code>, and for checking if a reconstruction point will actually be called rather than falling back to a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c->…<c- o>></c-></code> return. The 3 forms allow for 3 levels of construction, where each one defers to the next version by removing one layer of "information" until finally following back to the most basic form:</p>
   <ul>
    <li data-md>
     <p>the desired type to reconstruct ("tag"), the range, the iterator, and the sentinel;</p>
    <li data-md>
     <p>the desired type to reconstruct ("tag"), the iterator, and the sentinel, after stripping out the range if the previous <code class="highlight"><c- n>reconstruct</c-></code> did not find anything;</p>
    <li data-md>
     <p>the iterator and the sentinel, after dropping the tag if the previous <code class="highlight"><c- n>reconstruct</c-></code> attempt did not work and making sure at least one of <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>is_class_v</c-><c- o>&lt;</c-><c- n>iterator</c-><c- o>></c-></code>, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>is_class_v</c-><c- o>&lt;</c-><c- n>sentinal</c-><c- o>></c-></code>, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>is_enum_v</c-><c- o>&lt;</c-><c- n>iterator</c-><c- o>></c-></code>, or <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>is_enum_v</c-><c- o>&lt;</c-><c- n>sentinel</c-><c- o>></c-></code> is <code class="highlight">true</code>; and finally,</p>
    <li data-md>
     <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>iterator</c-><c- p>),</c-> <c- k>decltype</c-><c- p>(</c-><c- n>sentinel</c-><c- p>)</c-><c- o>></c-></code> if nothing else matches.</p>
   </ul>
   <p>This allows a developer to put a range back together at various levels of fidelity from its parts and pieces, giving us the ability to propagate the input type’s properties after modifying its iterators for some underlying work, algorithm or other effect. This concept is also the basis of the idea behind <a data-link-type="biblio" href="#biblio-p1739r4">[p1739r4]</a>, which was accepted in a lesser form for C++20 with the intent of this paper following up on it. Algorithm authors can use the extension point and the concepts to simplify their code or to add support for a broader variety of types: see <a href="#design-containers">further down in this proposal</a> for an example of a possible use case for making <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>split</c-></code> more robust in the presence of containers.</p>
   <p>Note that, when defining a reconstruction point, a normal user is NOT required to override all three potential customizations. A user may override one form, two forms, or all three forms, depending on what kind of information may be available to help make the best decision for reconstruction possible.</p>
   <h3 class="heading settled" data-level="3.1" id="design-borrowed"><span class="secno">3.1. </span><span class="content">Range? Why not "Borrowed Range"?</span><a class="self-link" href="#design-borrowed"></a></h3>
   <p>Previously, we required that the ranges being reconstructed modeled <code class="highlight"><c- n>borrowed_range</c-></code>, since that was an accurate indicator that the iterators and sentinel could potentially outlive the range itself. This was to prevent some issues in a previous design that used constructors. Since that is no longer based on constructors and with no chance of false positives, we no longer need to include that limitation. <code class="highlight"><c- n>borrowed_range</c-></code> is also too restrictive, as there are some cases where the resulting range is non-borrowed, but could be successfully reconstructed from some of its pieces. The concept is opt-in now by way of declaring an ADL-found <code class="highlight"><c- n>reconstruct</c-></code> function, any type can effectively decide for itself whether it could reconstruct properly. Note that this opens up usages for things that, if we had used <code class="highlight"><c- n>borrowed_range</c-></code>, would not have been reconstructible. Consider the following expression:</p>
<pre class="language-cpp highlight"><c- b>int</c-> <c- nf>f</c-> <c- p>(</c-><c- b>int</c-> <c- n>v</c-><c- p>)</c-> <c- p>{</c->
	<c- k>return</c-> <c- n>v</c-> <c- o>*</c-> <c- mi>2</c-><c- p>;</c->
<c- p>}</c->

<c- b>int</c-> <c- nf>main</c-> <c- p>()</c-> <c- p>{</c->
	<c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-> <c- n>vec</c-><c- p>{</c-><c- mi>1</c-><c- p>,</c-> <c- mi>2</c-><c- p>,</c-> <c- mi>3</c-><c- p>,</c-> <c- mi>4</c-><c- p>,</c-> <c- mi>5</c-><c- p>,</c-> <c- mi>6</c-><c- p>,</c-> <c- mi>7</c-><c- p>,</c-> <c- mi>8</c-><c- p>,</c-> <c- mi>9</c-><c- p>,</c-> <c- mi>10</c-><c- p>};</c->
	<c- n>std</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-> <c- n>some_span</c-><c- p>(</c-><c- n>vec</c-><c- p>);</c->
	<c- k>auto</c-> <c- n>transform</c-> <c- o>=</c-> <c- n>some_span</c->
		<c- o>|</c-> <c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>transform</c-><c- p>(</c-><c- n>f</c-><c- p>)</c->
		<c- o>|</c-> <c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>take</c-><c- p>(</c-><c- mi>5</c-><c- p>);</c->
	<c- c1>// ...</c->
	<c- k>return</c-> <c- mi>0</c-><c- p>;</c->
<c- p>}</c->
</pre>
   <p>This particular case is reconstructible as <code class="highlight"><c- n>span</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> is reconstructible. The original transformation view can be reconstructed here without the need to keep the <code class="highlight"><c- n>take_view</c-></code> intermediate wrapped around the two previous transformations, as the transform can be ignored on the first five elements by advancing the given <code class="highlight"><c- n>some_span</c-></code>'s <code class="highlight"><c- n>begin</c-><c- p>()</c-></code> by 5 elements. A smart <code class="highlight"><c- n>reconstruct</c-></code> call for <code class="highlight"><c- n>take_view</c-></code> does this (and is present in <a href="#wording-specification">§ 6.3 Proposed Library Wording</a>).</p>
   <h3 class="heading settled" data-level="3.2" id="design-multiple"><span class="secno">3.2. </span><span class="content">Multiple, Safe Reconstruction Points</span><a class="self-link" href="#design-multiple"></a></h3>
   <p>Consider a hypothetical <code class="highlight"><c- n>c_string_view</c-></code> type. It is impossible to, from normal <code class="highlight"><c- k>const</c-> <c- b>char</c-><c- o>*</c-></code> iterator pair ascertain the range is null-terminated and is thus a "C string". Therefore, a reconstruct for <code class="highlight"><c- n>c_string_view</c-></code> would not return a <code class="highlight"><c- n>c_string_view</c-></code>, but a normal <code class="highlight"><c- n>string_view</c-></code>.</p>
   <p>On the other hand, if there was a <code class="highlight"><c- n>c_string_sentinel</c-></code> sentinel with a <code class="highlight"><c- k>const</c-> <c- b>char</c-><c- o>*</c-></code> iterator that was preserved through a series of actions and algorithms, that kind of information would allow us to return a <code class="highlight"><c- n>c_string_view</c-></code> from a reconstruction operation.</p>
   <p>The <code class="highlight"><c- n>reconstruct</c-></code> extension point supports both of these scenarios:</p>
<pre class="language-cpp highlight"><c- k>class</c-> <c- nc>c_string_view</c-> <c- p>{</c->
	<c- d>/* blah... */</c->

	<c- c1>// reconstruct: with [const char*, const char*) iterators</c->
	<c- c1>// no guarantee it’s null terminated: decay to string_view</c->
	<c- k>friend</c-> <c- k>constexpr</c-> <c- n>std</c-><c- o>::</c-><c- n>string_view</c-> <c- n>reconstruct</c-> <c- p>(</c->
		<c- n>std</c-><c- o>::</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>c_string_view</c-><c- o>></c-><c- p>,</c->
		<c- k>const</c-> <c- b>char</c-><c- o>*</c-> <c- n>first</c-><c- p>,</c-> <c- k>const</c-> <c- b>char</c-><c- o>*</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-> <c- p>{</c->
		<c- k>return</c-> <c- n>std</c-><c- o>::</c-><c- n>string_view</c-><c- p>(</c-><c- n>first</c-><c- p>,</c-> <c- n>last</c-><c- p>);</c->
	<c- p>}</c->

	<c- c1>// reconstruct: with static [const char*, c_string_sentinel)</c->
	<c- c1>// static guarantee by type: return a c_string_view</c->
	<c- k>friend</c-> <c- k>constexpr</c-> <c- n>c_string_view</c-> <c- n>reconstruct</c-> <c- p>(</c->
		<c- n>std</c-><c- o>::</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>c_string_view</c-><c- o>></c-><c- p>,</c->
		<c- k>const</c-> <c- b>char</c-><c- o>*</c-> <c- n>first</c-><c- p>,</c-> <c- n>c_string_sentinel</c-><c- p>)</c-> <c- k>noexcept</c-> <c- p>{</c->
		<c- k>return</c-> <c- nf>c_string_view</c-><c- p>(</c-><c- n>first</c-><c- p>);</c->
	<c- p>}</c->
<c- p>};</c->
</pre>
   <p>This is a level of flexibility that is better than the Revision 0 constructor-based design, and can aid in providing better static guarantees while decaying gracefully in other situations.</p>
   <h3 class="heading settled" data-level="3.3" id="design-all"><span class="secno">3.3. </span><span class="content">Opt-in?</span><a class="self-link" href="#design-all"></a></h3>
   <p>Not all ranges can meet this requirement. Some ranges contain state which cannot be trivially propagated into the iterators, or state that cannot be reconstructed from the iterator/sentinel pair itself. However, most of the common ranges representing unbounded views, empty views, iterations viewing some section of non-owned storage, or similar can all be reconstructed from their iterator/iterator or iterator/sentinel pair.</p>
   <p>For example <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>single_view</c-></code> contains a <a href="http://eel.is/c++draft/range.semi.wrap">exposition-only semiregular-box template type ([ranges.semi.wrap])</a> which holds a value to iterate over. It would not be possible to reconstruct the exact same range (e.g., iterators pointing to the exact same object) with the semi-regular wrapper. Ranges should have the ability to select this syntax without having it happen to their type implicitly, or as for more information.</p>
   <p>This is why there are 4 levels to opt-in to support. If a user defines the 4-argument form which takes a <code class="highlight"><c- p>(</c-><c- n>tag</c-><c- p>,</c-> <c- n>range</c-><c- p>,</c-> <c- n>iterator</c-><c- p>,</c-> <c- n>sentinel</c-><c- p>)</c-></code> quadruplet, than they can use as much information may be available in the range, iterator, and sentinel to reproduce the original range. If they do not need that much information, they can opt-in to the 3-argument version which only takes the <code class="highlight"><c- p>(</c-><c- n>tag</c-><c- p>,</c-> <c- n>iterator</c-><c- p>,</c-> <c- n>sentinel</c-><c- p>)</c-></code> triplet. If they want to only deal with the original range and the tag (as an optimization, to save on <code class="highlight"><c- n>reconstruct</c-></code> potentially calling <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>r</c-><c- p>)</c-></code> and <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>r</c-><c- p>)</c-></code> on the range and calling the <code class="highlight"><c- p>(</c-><c- n>tag</c-><c- p>,</c-> <c- n>range</c-><c- p>,</c-> <c- n>iterator</c-><c- p>,</c-> <c- n>sentinel</c-><c- p>)</c-></code> version), they can define <code class="highlight"><c- n>reconstruct</c-></code> for just <code class="highlight"><c- p>(</c-><c- n>tag</c-><c- p>,</c-> <c- n>range</c-><c- p>)</c-></code>. And, finally, the most brief and sophisticated form is the <code class="highlight"><c- p>(</c-><c- n>iterator</c-><c- p>,</c-> <c- n>sentinel</c-><c- p>)</c-></code> form, which can reconstruct a range using information from only the iterator and/or sentinel.</p>
   <p>If the range opts-in to nothing, then there will always be a default return: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- n>Iterator</c-><c- p>,</c-> <c- n>Sentinel</c-><c- o>></c-></code>. This is effectively what any algorithm today already returns (sometimes it uses a hand-made pair type, likely because some iterator-pair usages may require the size to be stored and neither the iterator nor the sentinel can provide the size).</p>
   <h3 class="heading settled" data-level="3.4" id="design-applicable"><span class="secno">3.4. </span><span class="content">Applicability</span><a class="self-link" href="#design-applicable"></a></h3>
   <p>There are many ranges to which this is applicable, but only a handful in the standard library need or satisfy this. If <a data-link-type="biblio" href="#biblio-p1391r2">[p1391r2]</a> and <a data-link-type="biblio" href="#biblio-p1394r2">[p1394r2]</a> are accepted (they were), then the two most important view types -- <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Extent</c-><c- o>></c-></code> and <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>basic_string_view</c-><c- o>&lt;</c-><c- n>Char</c-><c- p>,</c-> <c- n>Traits</c-><c- o>></c-></code> -- will model the <em>spirit</em> of the concept (but lack the customization point to make it generic). <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- n>Iterator</c-><c- p>,</c-> <c- n>Sentinel</c-><c- p>,</c-> <c- n>Kind</c-><c- o>></c-></code> already fits this as well. By formalizing concepts in the standard, we can dependably and reliably assert that these properties continue to hold for these ranges. We intend to add a <code class="highlight"><c- k>constexpr</c-> <c- k>friend</c-> <c- n>reconstruct</c-></code> function to all of the non-<code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-></code> types.</p>
   <p>There are also upcoming ranges from <a data-link-type="biblio" href="#biblio-range-v3">[range-v3]</a> and elsewhere that could model this concept:</p>
   <ul>
    <li data-md>
     <p><a data-link-type="biblio" href="#biblio-p1255r4">[p1255r4]</a>'s <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>ref_maybe_view</c-></code>;</p>
    <li data-md>
     <p><a data-link-type="biblio" href="#biblio-p0009r9">[p0009r9]</a>'s <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>mdspan</c-></code>;</p>
    <li data-md>
     <p>and, soon to be proposed by this author for the purposes of output range algorithms, <a data-link-type="biblio" href="#biblio-range-v3">[range-v3]</a>'s <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>unbounded_view</c-></code>.</p>
   </ul>
   <p>And there are further range adaptor closure objects that could make use of this concept:</p>
   <ul>
    <li data-md>
     <p><code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>slice</c-></code>, <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>take_exactly</c-></code>, <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>drop_exactly</c-></code> and <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>take_last</c-></code> from <a data-link-type="biblio" href="#biblio-range-v3">[range-v3]</a></p>
   </ul>
   <p>Note that these changes will greatly aid other algorithm writers who want to preserve the same input ranges. In the future, the standard may provide an <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(...)</c-></code> algorithm for these types.</p>
   <h3 class="heading settled" data-level="3.5" id="design-overloads"><span class="secno">3.5. </span><span class="content">Why The Overloads?</span><a class="self-link" href="#design-overloads"></a></h3>
   <p>It has been questioned why there are four different potential extension points for <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-></code>. Indeed, most individuals observe that all of the necessary information required is the range and (possibly) any outstanding iterators. Their version of this paper — termed the "Alternative Design" — looks like this:</p>
<pre class="language-cpp highlight"><c- k>template</c-> <c- o>&lt;</c-><c- k>typename</c-> <c- nc>Range</c-><c- p>,</c-> <c- k>typename</c-> <c- nc>Iterator</c-><c- p>,</c-> <c- k>typename</c-> <c- nc>Sentinel</c-><c- o>></c->
<c- k>auto</c-> <c- n>reconstruct</c-><c- p>(</c-><c- n>Range</c-><c- o>&amp;&amp;</c-> <c- n>range</c-><c- p>,</c-> <c- n>Iterator</c-><c- o>&amp;&amp;</c-> <c- n>iterator</c-><c- p>,</c-> <c- n>Sentinel</c-><c- o>&amp;&amp;</c-> <c- n>sentinel</c-><c- p>);</c->
</pre>
   <p>It takes only the range, iterator, and sentinel. There are no tag types. There are no overloads which take: only an iterator and a sentinel; a tag, range, iterator and sentinel; a tag, iterator, and sentinel; or, a tag and a range.</p>
   <p>While the user only has to override one in this paper’s design, the design above provides <strong>only</strong> one customization point with no room for more or less information. However, many APIs which necessitate various forms of <code class="highlight"><c- n>reconstruct</c-></code> due to various circumstances when either wrapping certain function / algorithms or dealing with non-generic code within generic code.</p>
   <h4 class="heading settled" data-level="3.5.1" id="design-overloads-split"><span class="secno">3.5.1. </span><span class="content">Case 0: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>split</c-></code></span><a class="self-link" href="#design-overloads-split"></a></h4>
   <p>This case justifies <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>iterator</c-><c- p>,</c-> <c- n>iterator_or_sentinel</c-><c- p>)</c-></code>.</p>
   <p>The most frequently used way to reconstruct will be the version that takes a tag, an iterator, and another iterator/sentinel. This is motivated by a lot of code, including the code found in the implementation of <a data-link-type="biblio" href="#biblio-p1629r1">[p1629r1]</a>, <a data-link-type="biblio" href="#biblio-ztdtext">[ztd.text]</a>. More specifically, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>split_view</c-><c- o>&lt;</c-><c- n>V</c-><c- p>,</c-> <c- p>...</c-><c- o>></c-></code> stores the range it is made with, <code class="highlight"><c- n>V</c-></code>, within itself. It does not modify that original range: it only uses iterators from <code class="highlight"><c- n>V</c-></code> to present the <code class="highlight"><c- n>value_type</c-></code> / <code class="highlight"><c- n>reference</c-></code> as it iterates. <a data-link-type="biblio" href="#biblio-blog-views-split">This explanatory post</a> gets into the details, but the most important point is that <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>split_view</c-></code> does not present reconstructed slices of itself using strictly it’s iterator, it’s sentinel, and its range. It only presents a view of <code class="highlight"><c- p>[</c-><c- n>iterator</c-><c- p>,</c-> <c- n>iterator</c-><c- p>)</c-></code>, and completely ignores the sentinel type for the purposes of the presented <code class="highlight"><c- n>reference</c-></code> type (save for making sure the "current" iteration has not gone beyond-the-end).</p>
   <p>This means that the only available information is the <strong>type</strong> of <code class="highlight"><c- n>V</c-></code>, plus two of iterator objects (and <strong>not</strong> it’s sentinel object). This is crucial for, e.g. a <code class="highlight"><c- n>zstring</c-></code> like class, which uses <code class="highlight"><c- k>const</c-> <c- b>char</c-><c- o>*</c-></code> and some type of <code class="highlight"><c- n>zstring_sentinel</c-></code> type:</p>
<pre class="language-cpp highlight"><c- k>struct</c-> <c- nc>zstring_sentinel</c-> <c- p>{</c->
	<c- b>bool</c-> <c- k>operator</c-><c- o>==</c-><c- p>(</c-><c- b>char</c-> <c- k>const</c-><c- o>*</c-> <c- n>p</c-><c- p>)</c-> <c- k>const</c-> <c- p>{</c->
		<c- k>return</c-> <c- o>*</c-><c- n>p</c-> <c- o>==</c-> <c- sc>'\0'</c-><c- p>;</c->
	<c- p>}</c->
<c- p>};</c->

<c- k>struct</c-> <c- nc>zstring</c-> <c- o>:</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>view_interface</c-><c- o>&lt;</c-><c- n>zstring</c-><c- o>></c-> <c- p>{</c->
	<c- b>char</c-> <c- k>const</c-><c- o>*</c-> <c- n>p</c-> <c- o>=</c-> <c- k>nullptr</c-><c- p>;</c->
	<c- k>constexpr</c-> <c- nf>zstring</c-><c- p>()</c-> <c- o>=</c-> <c- k>default</c-><c- p>;</c->
	<c- k>constexpr</c-> <c- nf>zstring</c-><c- p>(</c-><c- b>char</c-> <c- k>const</c-><c- o>*</c-> <c- n>p</c-><c- p>)</c-> <c- o>:</c-> <c- n>p</c-><c- p>(</c-><c- n>p</c-><c- p>)</c-> <c- p>{</c-> <c- p>}</c->
	<c- k>constexpr</c-> <c- k>auto</c-> <c- n>begin</c-><c- p>()</c-> <c- k>const</c-> <c- p>{</c-> <c- k>return</c-> <c- n>p</c-><c- p>;</c-> <c- p>}</c->
	<c- k>constexpr</c-> <c- k>auto</c-> <c- n>end</c-><c- p>()</c-> <c- k>const</c-> <c- p>{</c-> <c- k>return</c-> <c- n>zstring_sentinel</c-><c- p>{};</c-> <c- p>}</c->

	<c- c1>// (1)</c->
	<c- k>friend</c-> <c- k>constexpr</c-> <c- n>std</c-><c- o>::</c-><c- n>string_view</c-> <c- n>reconstruct</c-><c- p>(</c->
		<c- n>std</c-><c- o>::</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>zstring</c-><c- o>></c-><c- p>,</c->
		<c- k>const</c-> <c- b>char</c-><c- o>*</c-> <c- n>f</c-><c- p>,</c->
		<c- k>const</c-> <c- b>char</c-><c- o>*</c-> <c- n>l</c-><c- p>)</c-> <c- k>noexcept</c-> <c- p>{</c->
		<c- k>return</c-> <c- n>std</c-><c- o>::</c-><c- n>string_view</c-><c- p>{</c-><c- n>f</c-><c- p>,</c-> <c- k>static_cast</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- b>size_t</c-><c- o>></c-><c- p>(</c-><c- n>l</c-> <c- o>-</c-> <c- n>f</c-><c- p>)};</c->
	<c- p>}</c->

	<c- c1>// (2)</c->
	<c- k>friend</c-> <c- k>constexpr</c-> <c- n>zstring</c-> <c- n>reconstruct</c-><c- p>(</c->
		<c- k>const</c-> <c- b>char</c-><c- o>*</c-> <c- n>f</c-><c- p>,</c->
		<c- n>zstring_sentinel</c-><c- p>)</c-> <c- k>noexcept</c-> <c- p>{</c->
		<c- k>return</c-> <c- n>zstring</c-><c- p>{</c-><c- n>f</c-><c- p>};</c->
	<c- p>}</c->
<c- p>};</c->
</pre>
   <p>The reconstruction point under <code class="highlight"><c- c1>// (1)</c-></code> is what gets used by <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>split</c-></code>. We clearly do not want to return a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- p>...</c-><c- o>></c-></code> type for this, given that the logical substring of a null-terminated string is just a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string_view</c-></code>. Reconstructible helps us accomplish this by letting us have varying customization points for different scenarios. Which, brings us to the next case that continues to serve as justification...</p>
   <p>This is required, especially if we would like to ensure that <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>split</c-></code> has optimal behavior.</p>
   <h4 class="heading settled" data-level="3.5.2" id="design-overloads-max-info"><span class="secno">3.5.2. </span><span class="content">Case 1: <code class="highlight"><c- n>zstring</c-></code> and <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>drop</c-></code></span><a class="self-link" href="#design-overloads-max-info"></a></h4>
   <p>This case justifies <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>Range</c-><c- p>,</c-> <c- n>iterator</c-><c- p>,</c-> <c- n>iterator_or_sentinel</c-><c- p>)</c-></code>, which covers the algorithms present in <a data-link-type="biblio" href="#biblio-ztdtext">[ztd.text]</a>, and <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>iterator</c-><c- p>,</c-> <c- n>iterator_or_sentinel</c-><c- p>)</c-></code>, which is the extension point’s form needed for <code class="highlight"><c- n>zstring</c-></code>.</p>
   <p>As shown in <a href="#design-overloads-split">Case 0</a>, the <code class="highlight"><c- n>zstring</c-></code> class has a second reconstruction point:</p>
<pre class="language-cpp highlight"><c- k>struct</c-> <c- nc>zstring</c-> <c- o>:</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>view_interface</c-><c- o>&lt;</c-><c- n>zstring</c-><c- o>></c-> <c- p>{</c->
	<c- c1>// …</c->

	<c- c1>// (2)</c->
	<c- k>friend</c-> <c- k>constexpr</c-> <c- n>zstring</c-> <c- n>reconstruct</c-><c- p>(</c->
		<c- k>const</c-> <c- b>char</c-><c- o>*</c-> <c- n>f</c-><c- p>,</c->
		<c- n>zstring_sentinel</c-><c- p>)</c-> <c- k>noexcept</c-> <c- p>{</c->
		<c- k>return</c-> <c- n>zstring</c-><c- p>{</c-><c- n>f</c-><c- p>};</c->
	<c- p>}</c->
	
	<c- c1>// …</c->
<c- p>};</c->
</pre>
   <p>This reconstruction point is paramount for <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>drop</c-></code> (and similar algorithms) to work correctly. <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>drop</c-></code> can be computed by simply incrementing the begin iterator by the provided <code class="highlight"><c- n>min</c-></code> count passed to the algorithm. So, that means the new <code class="highlight"><c- n>begin</c-><c- p>()</c-></code> on the desired <code class="highlight"><c- n>drop_view</c-></code> is <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>E</c-><c- p>)</c-> <c- o>+</c-> <c- n>min</c-><c- o>&lt;</c-><c- n>D</c-><c- o>></c-><c- p>(</c-><c- n>ranges</c-><c- o>::</c-><c- n>size</c-><c- p>(</c-><c- n>E</c-><c- p>),</c-> <c- n>F</c-><c- p>)</c-></code>, where <code class="highlight"><c- n>E</c-></code> is a range, and <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>E</c-><c- p>)</c-></code> is the end. For <code class="highlight"><c- n>zstring</c-></code>, this is where the second reconstruction point comes in handy. There is no constructor we can use to make <code class="highlight"><c- n>zstring</c-></code> behave as expected, but with <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-></code> we can re-constitute the <code class="highlight"><c- n>zstring</c-></code> properly if <code class="highlight"><c- n>E</c-></code> is a (potentially cv-qualified) <code class="highlight"><c- n>zstring</c-></code>:</p>
   <blockquote>
    <p>… Otherwise, if <code class="highlight"><c- n>T</c-></code> models both <code class="highlight"><c- n>random_access_range</c-></code> and <code class="highlight"><c- n>sized_range</c-></code>, […] then <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>,</c-> <c- n>E</c-><c- p>,</c-> <c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>E</c-><c- p>)</c-> <c- o>+</c-> <c- n>min</c-><c- o>&lt;</c-><c- n>D</c-><c- o>></c-><c- p>(</c-><c- n>ranges</c-><c- o>::</c-><c- n>size</c-><c- p>(</c-><c- n>E</c-><c- p>),</c-> <c- n>F</c-><c- p>),</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>E</c-><c- p>))</c-></code>, except that <code class="highlight"><c- n>E</c-></code> is evaluated only once.</p>
   </blockquote>
   <p>This will allow us to reconstitute the range. Note that we have 4 pieces here: the tag, range itself <code class="highlight"><c- n>E</c-></code>, the <code class="highlight"><c- n>iterator</c-></code> object (advanced by the minimum between the size of the range and <code class="highlight"><c- n>F</c-></code>), and the <code class="highlight"><c- n>sentinel</c-></code> object. <code class="highlight"><c- n>zstring</c-></code>, in this case, does not need the original range itself. But, this is fine: <code class="highlight"><c- n>reconstruct</c-></code> will drop the <code class="highlight"><c- n>range</c-></code> type to see if that extension point works, then drop the <code class="highlight"><c- n>tag</c-></code> object to see if the iterator/sentinel is enough. As it is in <code class="highlight"><c- n>zstring</c-></code>'s case, that will be the extension point called to reconstitute the <code class="highlight"><c- n>zstring</c-></code>. This does not mean all ranges can always drop all information given: see <a href="#design-overloads-efficiency">the transform view case</a> for an additional case where being able to pass in the original range actually matters.</p>
   <h4 class="heading settled" data-level="3.5.3" id="design-overloads-legacy"><span class="secno">3.5.3. </span><span class="content">Case 2: Legacy Iterator Code</span><a class="self-link" href="#design-overloads-legacy"></a></h4>
   <p>This case justifies <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>iterator</c-><c- p>,</c-> <c- n>iterator_or_sentinel</c-><c- p>)</c-></code>.</p>
   <p>There is too much code in the world that works off of, exclusively, iterators, and does not compose to a range type. Some of them mock semi-range interfaces, such as <code class="highlight"><c- n>UCharIterator</c-></code> <a data-link-type="biblio" href="#biblio-icuchariterator">from ICU</a>. Others are just quite literally <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>pair</c-><c- o>&lt;</c-><c- n>iterator</c-><c- p>,</c-> <c- n>iterator</c-><c- o>></c-></code> -like return values and structs with similar information. Whatever the case is, there is a wide body of preexisting code that can benefit from reconstruction even if the range type/range object is not directly available.</p>
   <p>There are also many ranges - such as <code class="highlight"><c- n>zstring</c-></code> above - which genuinely do not need range type information to be reconstructed. Both the iterator and the sentinel pair’s type information is enough to strongly identify ranges that are capable of this. Other types of ranges include most ranges in the C++20 ranges library: almost all of them have distinct iterator types paired with either a distinct sentinel type or a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>default_sentinel_t</c-></code>. Almost none of these need the original range in order to properly reconstruct and form an unambiguous set given just the iterator and the sentinel. Older <code class="highlight"><c- n>buffer_view</c-><c- o>&lt;</c-><c- n>T</c-><c- p>,</c-> <c- n>Bounds</c-><c- o>></c-></code> class types (the precursor to <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>span</c-></code> and <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>mdspan</c-></code>) also have iterators which are distinct to the class itself to traverse the</p>
   <p>It does not make sense to cut off all the pre-C++20 iterator-based algorithms and intermediates to not be able to take advantage of ranges code, even if only internally. Modernizing internals is still a useful goal, even if that leads to uses where they are bound to break it apart so that it can fit into a result structure or a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>pair</c-><c- o>&lt;</c-><c- n>It</c-><c- p>,</c-> <c- n>It</c-><c- o>></c-></code>-like return value from compatibility or API concerns.</p>
   <p>It also does not make sense to force a person to need to explicit specify every single combination of <code class="highlight"><c- p>(</c-><c- n>range_type</c-><c- p>,</c-> <c- p>(</c-><c- n>iterator</c-><c- p>,</c-> <c- n>sentinel</c-><c- p>))</c-></code> in order to be able to properly reconstruct something. For example, if the <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>iterator</c-><c- p>,</c-> <c- n>sentinel</c-><c- p>)</c-></code> does not exist, than the only way to reconstruct a <code class="highlight"><c- n>zstring</c-></code> if an algorithm or intermediate step happens to destroy the original range and turn it into a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- k>const</c-> <c- b>char</c-><c- o>*</c-><c- p>,</c-> <c- n>zstring_sentinel</c-><c- o>></c-></code> is to write multiple extension points:</p>
<pre class="language-cpp highlight"><c- k>struct</c-> <c- nc>zstring</c-> <c- o>:</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>view_interface</c-><c- o>&lt;</c-><c- n>zstring</c-><c- o>></c-> <c- p>{</c->
	<c- c1>// …</c->

	<c- c1>// (2.1)</c->
	<c- k>friend</c-> <c- k>constexpr</c-> <c- n>zstring</c-> <c- n>reconstruct</c-><c- p>(</c->
		<c- n>std</c-><c- o>::</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>zstring</c-><c- o>></c-><c- p>,</c->
		<c- k>const</c-> <c- b>char</c-><c- o>*</c-> <c- n>f</c-><c- p>,</c->
		<c- n>zstring_sentinel</c-><c- p>)</c-> <c- k>noexcept</c-> <c- p>{</c->
		<c- k>return</c-> <c- n>zstring</c-><c- p>{</c-><c- n>f</c-><c- p>};</c->
	<c- p>}</c->

	<c- c1>// (2.2)</c->
	<c- k>friend</c-> <c- k>constexpr</c-> <c- n>zstring</c-> <c- n>reconstruct</c-><c- p>(</c->
		<c- n>std</c-><c- o>::</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c->
			<c- k>const</c-> <c- b>char</c-><c- o>*</c-><c- p>,</c-> <c- n>zstring_sentinel</c->
		<c- o>>></c-><c- p>,</c->
		<c- k>const</c-> <c- b>char</c-><c- o>*</c-> <c- n>f</c-><c- p>,</c->
		<c- n>zstring_sentinel</c-><c- p>)</c-> <c- k>noexcept</c-> <c- p>{</c->
		<c- k>return</c-> <c- n>zstring</c-><c- p>{</c-><c- n>f</c-><c- p>};</c->
	<c- p>}</c->

	<c- c1>// …</c->
<c- p>};</c->
</pre>
   <p>Right now, we are at 2. But as we get more and more ranges that are simple wrappers with some associated behavior, we may need to define even more if we do not have the base-case <code class="highlight"><c- n>iterator</c-><c- p>,</c-> <c- n>sentinel</c-></code> extension point. This is not a tenable solution to the problem over a long period of time.</p>
   <h4 class="heading settled" data-level="3.5.4" id="design-overloads-efficiency"><span class="secno">3.5.4. </span><span class="content">Case 3: <code class="highlight"><c- n>transform_view</c-></code></span><a class="self-link" href="#design-overloads-efficiency"></a></h4>
   <p>This case justifies <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>range</c-><c- p>,</c-> <c- n>iterator</c-><c- p>,</c-> <c- n>iterator_or_sentinel</c-><c- p>)</c-></code>.</p>
   <p>As explained in <a data-link-type="biblio" href="#biblio-p2415">[p2415]</a> and earlier papers that changed the <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-></code> model to not always treat all views as cheaply-copied entities, we sometimes need to forward ranges through algorithms or take ranges by reference in order to have more useful information about them and make more intelligent decisions about them. This applies to cases like <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>transform_view</c-></code>, where having access to the original range (as a value or by r-value reference) allows us to perform a much more efficient reconstruction.</p>
   <blockquote>
<pre class="language-cpp highlight"><c- k>friend</c-> <c- k>constexpr</c-> <c- k>auto</c->
<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>transform_view</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>transform_view</c-><c- o>&amp;</c-> <c- n>original</c->‚
	<c- n>iterator</c-><c- o>&lt;</c-><c- n>iterator_condition</c-><c- o>></c-> <c- n>first</c-><c- p>,</c->
	<c- n>sentinel</c-><c- o>&lt;</c-><c- n>sentinel_condition</c-><c- o>></c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>(</c-><c- n>see</c-><c- o>-</c-><c- n>below</c-><c- p>);</c->

<c- k>friend</c-> <c- k>constexpr</c-> <c- k>auto</c->
<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>transform_view</c-><c- o>></c-><c- p>,</c-> <c- n>transform_view</c-><c- o>&amp;&amp;</c-> <c- n>original</c->‚
	<c- n>iterator</c-><c- o>&lt;</c-><c- n>iterator_condition</c-><c- o>></c-> <c- n>first</c-><c- p>,</c->
	<c- n>sentinel</c-><c- o>&lt;</c-><c- n>sentinel_condition</c-><c- o>></c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>(</c-><c- n>see</c-><c- o>-</c-><c- n>below</c-><c- p>);</c->
</pre>
   </blockquote>
   <p>The user provides us with a range here, similar to other use cases in the wild (and, perhaps, the majority use case) (for example, most of <a data-link-type="biblio" href="#biblio-ztdtext">[ztd.text]</a> consumes its ranges by-value, and can easily afford to move not only the iterator and sentinel but the range that was passed down to it). When the user can give us the original <code class="highlight"><c- n>transform_view</c-></code>, we can choose between a far more efficient move of not only the guts of the iterator and sentinel, but also of the <code class="highlight"><c- n>original</c-><c- p>.</c-><c- n>fun</c-></code> <em>exposition-only</em> member present. This is a key efficiency for more wrapping and nested ranges, and can matter for moving out objects which may allocate (such as a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>transform_view</c-></code> with a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>function</c-><c- o>&lt;</c->…<c- o>></c-></code>) contained inside. In the case of an l-value reference, we copy.</p>
   <p>It is important to note that we only use the four-argument, range-provided form in this extension point here because we do not want to pay the cost of re-forming the <code class="highlight"><c- n>transform_view</c-></code> when only handed the iterator and the sentinel. Previous versions of this paper had a reconstruction point which used both the <code class="highlight"><c- n>iterator</c-></code> and the <code class="highlight"><c- n>sentinel</c-></code> of <code class="highlight"><c- n>transform_view</c-></code> only, which necessitated copying the original function. While recreating the view, this operation may not be cheap (in both <code class="highlight"><c- n>transform_view</c-></code>'s case and many other views’s cases).</p>
   <h3 class="heading settled" data-level="3.6" id="design-alternative0"><span class="secno">3.6. </span><span class="content">Alternative Design: <code class="highlight"><c- p>(</c-><c- n>range</c-><c- p>,</c-> <c- n>iterator</c-><c- p>,</c-> <c- n>sentinel</c-><c- p>)</c-></code> Reconstruction Point</span><a class="self-link" href="#design-alternative0"></a></h3>
   <p>We could, under a different paradigm that does not take a tag, take the actual range instead and then simply ignore the range argument. Consider, once again, the <code class="highlight"><c- n>zstring</c-></code> class used in the above Cases:</p>
<pre class="language-cpp highlight"><c- k>struct</c-> <c- nc>zstring</c-> <c- o>:</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>view_interface</c-><c- o>&lt;</c-><c- n>zstring</c-><c- o>></c-> <c- p>{</c->
	<c- c1>// …</c->

	<c- c1>// (New Extension: range, iterator, sentinel)</c->
	<c- k>template</c-> <c- o>&lt;</c-><c- k>typename</c-> <c- nc>Range</c-><c- o>></c->
	<c- k>friend</c-> <c- k>constexpr</c-> <c- n>zstring</c-> <c- n>reconstruct</c-><c- p>(</c->
		<c- n>Range</c-><c- o>&amp;&amp;</c-><c- p>,</c-> <c- c1>// ignored</c->
		<c- k>const</c-> <c- b>char</c-><c- o>*</c-> <c- n>f</c-><c- p>,</c->
		<c- n>zstring_sentinel</c-><c- p>)</c-> <c- k>noexcept</c-> <c- p>{</c->
		<c- k>return</c-> <c- n>zstring</c-><c- p>{</c-><c- n>f</c-><c- p>};</c->
	<c- p>}</c->

	<c- c1>// …</c->
<c- p>};</c->
</pre>
   <p>This, however, has a few problems.</p>
   <p>Consider <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>split</c-></code>. It does not want to fully reconstruct the <code class="highlight"><c- k>this</c-><c- o>-></c-><c- n>base</c-></code> (exposition-only) range! It only wants to recreate a piece of itself, and keep using <code class="highlight"><c- k>this</c-><c- o>-></c-><c- n>base</c-></code> in future iterations of it’s reference code. Use of this kind of extension point requires that a range must exist or must be available to pass in. This is <strong>not possible</strong> in the general sense: ranges (and now, views) are no longer required to be default constructible, so we cannot always expect an algorithm to use the original range (or just a default-constructed range, assuming advanced knowledge where you expect the range argument to not be used).</p>
   <p>As a base, having the <code class="highlight"><c- p>[</c-><c- n>iterator</c-><c- p>,</c-> <c- n>sentinel</c-><c- p>)</c-></code> overload is a proper way to signal "I want what is minimally reconstructible from strictly this information, and without paying the cost of potentially rebuilding the entire original range". This is critical in the case of, for example, a follow-on paper which can build on this to request different <strong>types</strong> of ranges be re-created, knowing that only the iterators can be used for such an operation. An example of such can be found for a Future C++ Ranges Proposal in <a href="#design-containers">§ 3.7 Expanding to Owning Containers and More?</a>.</p>
   <h3 class="heading settled" data-level="3.7" id="design-containers"><span class="secno">3.7. </span><span class="content">Expanding to Owning Containers and More?</span><a class="self-link" href="#design-containers"></a></h3>
   <p>There is a desire to have <code class="highlight"><c- n>reconstruct</c-></code> automatically apply to things like <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string</c-></code> and <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code>. For example, it would be nice if <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>split</c-></code> could take in a <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string</c-></code> and know to boil it down to <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string_view</c-></code> pieces rather than <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- n>impl</c-><c- o>-</c-><c- n>defined</c-><c- o>-</c-><c- n>iterator</c-><c- p>,</c-> <c- n>impl</c-><c- o>-</c-><c- n>defined</c-><c- o>-</c-><c- n>iterator</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange_kind</c-><c- o>::</c-><c- n>sized</c-><c- o>></c-></code>. However, the idea should be swiftly rejected in a generic application like this for a very good reason:</p>
   <blockquote>
    <p>… It is, however, possible that future more refined concepts would no longer be modelled by an input type erased in the above fashion. For this reason Casey Carter argued against changing views::all and it was dropped from this proposal.</p>
    <p>[The current proposal does not suffer from this uncertainty, because we are preserving the exact input type and there is no erasure.]</p>
    <p>— <a data-link-type="biblio" href="#biblio-p1739r4">Hannes Hauswedell, P1739r4</a></p>
   </blockquote>
   <p>Changes of this magnitude have to be made on a case-by-case basis. For example, for <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>split</c-></code>, a future paper can use a sequence of potential reconstruction steps to try to pick the right reconstruction algorithm. For example, its <i><code class="highlight"><c- n>find</c-><c- o>-</c-><c- n>next</c-></code></i> exposition-only function could use the reconstruction traits in the code here to "select" a potentially better reconstruction point, before simply falling back to the baseline reconstruction call:</p>
   <blockquote>
<pre class="language-cpp highlight"><c- k>constexpr</c-> <c- k>auto</c-> <c- n>find</c-><c- o>-</c-><c- n>next</c-><c- p>(</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-> <c- n>it</c-><c- p>);</c-> <c- c1>// exposition only</c->
</pre>
    <p><em>Effects</em>: Equivalent to:</p>
<pre class="language-cpp highlight"><c- k>auto</c-> <c- p>[</c-><c- n>b</c-><c- p>,</c-> <c- n>e</c-><c- p>]</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>search</c-><c- p>(</c-><c- n>subrange</c-><c- p>(</c-><c- n>it</c-><c- p>,</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>base_</c-><c- p>)),</c-> <c- n>pattern_</c-><c- p>);</c->
<c- k>if</c-> <c- p>(</c-><c- n>b</c-> <c- o>!=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>base_</c-><c- p>)</c-> <c- o>&amp;&amp;</c-> <c- n>ranges</c-><c- o>::</c-><c- n>empty</c-><c- p>(</c-><c- n>pattern_</c-><c- p>))</c-> <c- p>{</c->
  <c- o>++</c-><c- n>b</c-><c- p>;</c->
  <c- o>++</c-><c- n>e</c-><c- p>;</c->
<c- p>}</c->
<c- k>if</c-> <c- k>constexpr</c-> <c- p>(</c-><c- n>ranges</c-><c- o>::</c-><c- n>reconstructible_range</c-><c- o>&lt;</c-><c- n>V</c-><c- p>,</c-> <c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-><c- p>,</c-> <c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c-><c- p>)</c-> <c- p>{</c->
	<c- k>return</c-> <c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-><c- p>,</c-> <c- n>b</c-><c- p>,</c-> <c- n>e</c-><c- p>);</c->
<c- p>}</c->
<c- k>else</c-> <c- k>if</c-> <c- k>constexpr</c-> <c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>is_const_v</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>range_value_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c->
	<c- o>&amp;&amp;</c-> <c- n>is</c-><c- o>-</c-><c- b>char</c-><c- o>-</c-><c- n>type</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>range_value_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c->
	<c- o>&amp;&amp;</c-> <c- n>ranges</c-><c- o>::</c-><c- n>reconstructible_range</c-><c- o>&lt;</c->
		<c- n>basic_string_view</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>range_value_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c-><c- p>,</c->
		<c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-><c- p>,</c-> <c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c->
	<c- o>></c-><c- p>)</c-> <c- p>{</c->
	<c- k>using</c-> <c- n>_Tag</c-> <c- o>=</c-> <c- n>in_place_type_t</c-><c- o>&lt;</c->
		<c- n>basic_string_view</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>range_value_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c->
	<c- o>>></c-><c- p>;</c->
	<c- k>return</c-> <c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>_Tag</c-><c- p>(),</c-> <c- n>b</c-><c- p>,</c-> <c- n>e</c-><c- p>);</c->
<c- p>}</c->
<c- k>else</c-> <c- k>if</c-> <c- k>constexpr</c-> <c- p>(</c-><c- n>ranges</c-><c- o>::</c-><c- n>reconstructible_range</c-><c- o>&lt;</c->
	<c- n>span</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>range_value_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c-><c- p>,</c->
	<c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-><c- p>,</c-> <c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c->
<c- o>></c-><c- p>)</c-> <c- p>{</c->
	<c- k>using</c-> <c- n>_Tag</c-> <c- o>=</c-> <c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>span</c-><c- o>&lt;</c-><c- n>ranges</c-><c- o>::</c-><c- n>range_value_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>>></c-><c- p>;</c->
	<c- k>return</c-> <c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>_Tag</c-><c- p>(),</c-> <c- n>b</c-><c- p>,</c-> <c- n>e</c-><c- p>);</c->
<c- p>}</c->
<c- k>else</c-> <c- p>{</c->
	<c- k>return</c-> <c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-><c- p>,</c-> <c- n>b</c-><c- p>,</c-> <c- n>e</c-><c- p>);</c->
<c- p>}</c->
</pre>
   </blockquote>
   <p>The above code is not necessarily exactly correct (e.g., one would need to accommodate for instantiation errors in <code class="highlight"><c- n>basic_string_view</c-></code> for improper types, and so carefully restructure the <code class="highlight"><c- k>if</c-> <c- k>constexpr</c-></code> checks), but overall that is how a future paper might better improve the <code class="highlight"><c- n>value_type</c-></code>s for <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>views</c-><c- o>::</c-><c- n>split_view</c-></code>. This paper does not engage in this fix because it focuses purely on reconstruction and not anything else: future work is welcome.</p>
   <p>More pointedly, however, this is a choice that has to be made on an algorithm-by-algorithm and view-by-view basis. It is not something that can be <strong>generally</strong> applied to every single view that wishes to attempt reconstruction. This is where the concepts for checking if there exists an ADL-callable version of <code class="highlight"><c- n>reconstruct</c-></code>, and why they are put into the standard. As demonstrated in the wording for <a href="#wording-specification-views_take">take_view</a> and <a href="#wording-specification-views_drop">drop_view</a>, the concept can simplify the specification and open it to a wider range of potentially reconstructible types, rather than a few hand-picked ones. Users can also use this for their own algorithms to apply optimizations, as demonstrated in the case of a potentially enhanced <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>split</c-></code> above.</p>
   <h2 class="heading settled" data-level="4" id="experience"><span class="secno">4. </span><span class="content">Deployment Experience</span><a class="self-link" href="#experience"></a></h2>
   <p>This change was motivated by Hannes Hauswedell’s <a data-link-type="biblio" href="#biblio-p1739r4">[p1739r4]</a> and became very important for the ranges work done with text encoding. There is a C++17 implementation <a href="https://github.com/soasis/text/blob/main/include/ztd/ranges/reconstruct.hpp">at the ztd.text repository here</a>, which is an implementation for the interface needed for <a data-link-type="biblio" href="#biblio-p1629r1">[p1629r1]</a>. It is meant to solve the deployment issues with P1739’s merging into the Standard.</p>
   <h2 class="heading settled" data-level="5" id="impact"><span class="secno">5. </span><span class="content">Impact</span><a class="self-link" href="#impact"></a></h2>
   <p>As a feature that is opt-in thanks to the <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-></code> Customization Point Object design, no currently created range or previously made range outside of the standard library is affected.</p>
   <p>Furthermore, this is a new and separate set of concepts. It is not to be added to the base <code class="highlight"><c- n>Range</c-></code> concept, or added to any other concept. It is to be applied separately to the types which can reasonably support it for the benefit of algorithms and code which can enhance the quality of their implementation.</p>
   <p>Finally, Hannes Hauswedell’s <a data-link-type="biblio" href="#biblio-p1739r4">[p1739r4]</a> with the explicit intention to mark certain ranges as reconstructible by hardcoding their behavior into the standard and come back with an opt-in fix during the C++23 cycle. This paper completes that promise.s</p>
   <h2 class="heading settled" data-level="6" id="wording"><span class="secno">6. </span><span class="content">Proposed Changes</span><a class="self-link" href="#wording"></a></h2>
   <p>The following wording is relative to the latest C++ Draft paper.</p>
   <h3 class="heading settled" data-level="6.1" id="wording-feature"><span class="secno">6.1. </span><span class="content">Feature Test Macro</span><a class="self-link" href="#wording-feature"></a></h3>
   <p>This paper results in a concept to help guide the further development of standard ranges and simplify their usages in generic contexts. There is one proposed feature test macro, <code class="highlight"><c- n>__cpp_lib_reconstructible_range</c-></code>, which is to be input into the standard and then explicitly updated every time a <code class="highlight"><c- n>reconstruct</c-></code> from a is added to reflect the new wording. We hope that by putting this in the standard early, most incoming ranges will be checked for compatibility with <code class="highlight"><c- n>iterator_reconstructible_range</c-></code> and <code class="highlight"><c- n>reconstructible_range</c-></code>.</p>
   <h3 class="heading settled" data-level="6.2" id="wording-intent"><span class="secno">6.2. </span><span class="content">Intent</span><a class="self-link" href="#wording-intent"></a></h3>
   <p>The intent of this wording is to provide greater generic coding guarantees and optimizations by allowing for a class of ranges and views that model the new exposition-only definitions of a reconstructible range:</p>
   <ul>
    <li data-md>
     <p>add a new feature test macro for reconstructible ranges to cover constructor changes;</p>
    <li data-md>
     <p>add a new customization point object for <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-></code>;</p>
    <li data-md>
     <p>add the customization point to many different ranges that can be reconstructed (<code class="highlight"><c- n>transform_view</c-></code>, <code class="highlight"><c- n>split_view</c-></code>, <code class="highlight"><c- n>subrange</c-></code>, <code class="highlight"><c- n>basic_string_view</c-></code>, <code class="highlight"><c- n>span</c-></code>, <code class="highlight"><c- n>iota_view</c-></code>);</p>
    <li data-md>
     <p>add three new concepts to <a href="http://eel.is/c++draft/range.req">[range.req</a>];</p>
    <li data-md>
     <p>and, use the concept in a few algorithms to return better versions of themselves (<code class="highlight"><c- n>drop_view</c-></code> and <code class="highlight"><c- n>take_view</c-></code>).</p>
   </ul>
   <h3 class="heading settled" data-level="6.3" id="wording-specification"><span class="secno">6.3. </span><span class="content">Proposed Library Wording</span><a class="self-link" href="#wording-specification"></a></h3>
   <h4 class="heading settled" data-level="6.3.1" id="wording-specification-feature_test"><span class="secno">6.3.1. </span><span class="content">Add a feature test macro <code class="highlight"><c- n>__cpp_lib_reconstructible_range</c-></code>.</span><a class="self-link" href="#wording-specification-feature_test"></a></h4>
   <p><em>Editor’s Note: Substitute appropriate value if plenary accepted.</em></p>
<pre class="language-cpp highlight"><c- cp>#define __cpp_lib_reconstructible_range 2022MML </c-><c- c1>// also in &lt;ranges></c->
</pre>
   <h4 class="heading settled" data-level="6.3.2" id="wording-specification-reconstruct_cpo_synopsis"><span class="secno">6.3.2. </span><span class="content">Insert into §24.2 Header <code class="highlight"><c- o>&lt;</c-><c- n>ranges</c-><c- o>></c-></code> Synopsis <a href="http://eel.is/c++draft/ranges.syn">[ranges.syn</a>] a new customization point object in the inline namespace:</span><a class="self-link" href="#wording-specification-reconstruct_cpo_synopsis"></a></h4>
   <blockquote> <code class="highlight"><c- k>namespace</c-> <c- n>std</c-><c- o>::</c-><c- n>ranges</c-> <c- p>{</c-> <br> <c- kr>inline</c-> <c- k>namespace</c-> <c- n>unspecified</c-> <c- p>{</c-> <br> … <br> <br> <ins><c- kr>inline</c-> <c- k>constexpr</c-> <i><c- n>unspecified</c-> </i><c- n>reconstruct</c-> <c- o>=</c-> <c- n>unspecified</c-><c- p>;</c-> </ins><br> <br> … <br> <c- p>}</c-> <br> … <br> <br> <ins> <c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>It</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Sen</c-> <c- o>=</c-> <c- n>It</c-><c- o>></c-> <br>   <c- k>using</c-> <c- n>iterator_reconstruct_t</c-> <c- o>=</c-> <c- k>decltype</c-><c- p>(</c-><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-> <br>     <c- n>declval</c-><c- o>&lt;</c-><c- n>It</c-><c- o>></c-><c- p>(),</c-> <c- n>declval</c-><c- o>&lt;</c-><c- n>Sen</c-><c- o>></c-><c- p>()</c-> <br>   <c- p>));</c-> <br> <br> <c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <br>   <c- k>class</c-> <c- nc>It</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>,</c-> <br>   <c- k>class</c-> <c- nc>Sen</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>sentinel_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-> <br>   <c- k>using</c-> <c- n>reconstruct_t</c-> <c- o>=</c-> <c- k>decltype</c-><c- p>(</c-><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-> <br>     <c- n>in_place_type</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>,</c-> <c- n>declval</c-><c- o>&lt;</c-><c- n>It</c-><c- o>></c-><c- p>(),</c-> <c- n>declval</c-><c- o>&lt;</c-><c- n>Sen</c-><c- o>></c-><c- p>()</c-> <br>   <c- p>));</c-> <br> <br> <c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>T</c-><c- p>,</c-> <br>   <c- k>class</c-> <c- nc>Tag</c-> <c- o>=</c-> <c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>,</c-> <br>   <c- k>class</c-> <c- nc>It</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>,</c-> <br>   <c- k>class</c-> <c- nc>Sen</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>sentinel_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>>></c-> <br>   <c- k>using</c-> <c- n>range_iterator_reconstruct_t</c-> <c- o>=</c-> <c- k>decltype</c-><c- p>(</c-><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-> <br>     <c- n>in_place_type</c-><c- o>&lt;</c-><c- n>Tag</c-><c- o>></c-><c- p>,</c-> <c- n>declval</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>(),</c-> <c- n>declval</c-><c- o>&lt;</c-><c- n>It</c-><c- o>></c-><c- p>(),</c-> <c- n>declval</c-><c- o>&lt;</c-><c- n>Sen</c-><c- o>></c-><c- p>()</c-> <br>   <c- p>));</c-> <br> </ins> <br> … <br> <br> <ins> <c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>It</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Sen</c-> <c- o>=</c-> <c- n>It</c-><c- o>></c-> <br>   <c- k>concept</c-> <c- nc>iterator_reconstructible_range</c-> <c- o>=</c-> <i><c- n>see</c-> <c- n>below</c-><c- p>;</c-></i> <br> <br> <c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>Tag</c-><c- p>,</c-> <br>   <c- k>class</c-> <c- nc>It</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <br>   <c- k>class</c-> <c- nc>Sen</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>sentinel_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></c-> <br>   <c- k>concept</c-> <c- nc>reconstructible_range</c-> <c- o>=</c-> <i><c- n>see</c-> <c- n>below</c-><c- p>;</c-></i> <br> <br> <c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>R</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Tag</c-> <c- o>=</c-> <c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <br>   <c- k>class</c-> <c- nc>It</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <br>   <c- k>class</c-> <c- nc>Sen</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>sentinel_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></c-> <br>   <c- k>concept</c-> <c- nc>range_iterator_reconstructible_range</c-> <c- o>=</c-> <i><c- n>see</c-> <c- n>below</c-><c- p>;</c-></i> <br> </ins><br> … <br><c- p>}</c-> </code> </blockquote>
   <h4 class="heading settled" data-level="6.3.3" id="wording-specification-concepts"><span class="secno">6.3.3. </span><span class="content">Insert into §24.4.2 Ranges <a href="http://eel.is/c++draft/range.req#range.range">[range.range</a>]'s after paragraph 7, one additional paragraph:</span><a class="self-link" href="#wording-specification-concepts"></a></h4>
   <blockquote>
    <ins>
     <sup>8</sup> The concepts <code class="highlight"><c- n>iterator_reconstructible_range</c-></code>, <code class="highlight"><c- n>reconstructible_range</c-></code>, and <code class="highlight"><c- n>range_iterator_reconstructible_range</c-></code> concepts describe the requirements on ranges that are efficiently constructible from certain iterator and sentinel types, alongside possible additional information from the range itself. 
<pre class="language-cpp highlight"><c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>It</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Sen</c-> <c- o>=</c-> <c- n>It</c-><c- o>></c->
	<c- k>concept</c-> <c- nc>iterator_reconstructible_range</c-> <c- o>=</c->
	<c- p>(</c-><c- n>is_class_v</c-><c- o>&lt;</c-><c- n>It</c-><c- o>></c-> <c- o>||</c-> <c- n>is_class_v</c-><c- o>&lt;</c-><c- n>Sen</c-><c- o>></c->
		<c- o>||</c-> <c- n>is_enum_v</c-><c- o>&lt;</c-><c- n>It</c-><c- o>></c-> <c- o>||</c-> <c- n>is_enum_v</c-><c- o>&lt;</c-><c- n>Sen</c-><c- o>></c-><c- p>)</c->
	<c- o>&amp;&amp;</c-> <c- k>requires</c-> <c- p>(</c-><c- n>It</c-> <c- n>first</c-><c- p>,</c-> <c- n>Sen</c-> <c- n>last</c-><c- p>)</c-> <c- p>{</c->
		<c- n>reconstruct</c-><c- p>(</c->
			<c- n>forward</c-><c- o>&lt;</c-><c- n>It</c-><c- o>></c-><c- p>(</c-><c- n>first</c-><c- p>),</c->
			<c- n>forward</c-><c- o>&lt;</c-><c- n>Sen</c-><c- o>></c-><c- p>(</c-><c- n>last</c-><c- p>)</c->
		<c- p>);</c->
	<c- p>};</c->

<c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>Tag</c-><c- p>,</c->
	<c- k>class</c-> <c- nc>It</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c->
	<c- k>class</c-> <c- nc>Sen</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>sentinel_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></c->
	<c- k>concept</c-> <c- nc>reconstructible_range</c-> <c- o>=</c->
	<c- n>ranges</c-><c- o>::</c-><c- n>range</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c->
	<c- o>&amp;&amp;</c-> <c- p>(</c-><c- n>iterator_reconstructible_range</c-><c- o>&lt;</c-><c- n>It</c-><c- p>,</c-> <c- n>Sen</c-><c- o>></c->
	<c- o>||</c-> <c- k>requires</c-> <c- p>(</c-><c- n>It</c-> <c- n>first</c-><c- p>,</c-> <c- n>Sen</c-> <c- n>last</c-><c- p>)</c-> <c- p>{</c->
		<c- n>reconstruct</c-><c- p>(</c->
			<c- n>in_place_type</c-><c- o>&lt;</c-><c- n>Tag</c-><c- o>></c-><c- p>,</c->
			<c- n>move</c-><c- p>(</c-><c- n>first</c-><c- p>),</c->
			<c- n>move</c-><c- p>(</c-><c- n>last</c-><c- p>)</c->
		<c- p>);</c->
	<c- p>});</c->

<c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>R</c-><c- p>,</c-> <c- k>class</c-> <c- nc>Tag</c-> <c- o>=</c-> <c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c->
	<c- k>class</c-> <c- nc>It</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c->
	<c- k>class</c-> <c- nc>Sen</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>sentinel_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></c->
	<c- k>concept</c-> <c- nc>range_iterator_reconstructible_range</c-> <c- o>=</c->
	<c- n>ranges</c-><c- o>::</c-><c- n>range</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c->
	<c- o>&amp;&amp;</c-> <c- p>(</c-><c- n>reconstructible_range</c-><c- o>&lt;</c-><c- n>Tag</c-><c- p>,</c-> <c- n>It</c-><c- p>,</c-> <c- n>Sen</c-><c- o>></c->
	<c- o>||</c-> <c- k>requires</c-> <c- p>(</c-><c- n>R</c-> <c- n>range</c-><c- p>,</c-> <c- n>It</c-> <c- n>first</c-><c- p>,</c-> <c- n>Sen</c-> <c- n>last</c-><c- p>)</c-> <c- p>{</c->
		<c- n>reconstruct</c-><c- p>(</c->
			<c- n>in_place_type</c-><c- o>&lt;</c-><c- n>Tag</c-><c- o>></c-><c- p>,</c->
			<c- n>forward</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>(</c-><c- n>range</c-><c- p>),</c->
			<c- n>forward</c-><c- o>&lt;</c-><c- n>It</c-><c- o>></c-><c- p>(</c-><c- n>first</c-><c- p>),</c->
			<c- n>forward</c-><c- o>&lt;</c-><c- n>Sen</c-><c- o>></c-><c- p>(</c-><c- n>last</c-><c- p>)</c->
		<c- p>);</c->
	<c- p>});</c->
</pre>
     <p><sup>9</sup> Let <code class="highlight"><c- n>r</c-></code> be a range with type <code class="highlight"><c- n>R</c-></code>, <code class="highlight"><c- n>T</c-></code> be some type, <code class="highlight"><c- n>i</c-></code> be an iterator of type <code class="highlight"><c- n>I</c-></code> and <code class="highlight"><c- n>s</c-></code> be a sentinel of type <code class="highlight"><c- n>S</c-></code>.</p>
     <dl>
      <dd>
       <sup>9.1</sup> — Let <code class="highlight"><c- n>it_sen_re_range</c-></code> be the result of <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>i</c-><c- p>,</c-> <c- n>s</c-><c- p>)</c-></code> if <code class="highlight"><c- n>I</c-></code> and <code class="highlight"><c- n>S</c-></code> satisfy <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>iterator_reconstructible_range</c-></code>. <code class="highlight"><c- n>r</c-></code> models <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>iterator_reconstructible_range</c-></code> if 
       <dl>
        <dd>— <code class="highlight"><c- n>i</c-> <c- o>==</c-> <c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>it_sen_re_range</c-><c- p>)</c-></code> is <code class="highlight">true</code>, and
        <dd>— <code class="highlight"><c- n>s</c-> <c- o>==</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>it_sen_re_range</c-><c- p>)</c-></code> is <code class="highlight">true</code>.
       </dl>
      <dd>
       <sup>9.2</sup> — Let <code class="highlight"><c- n>re_range</c-></code> be the result of <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>>></c-><c- p>,</c-> <c- n>i</c-><c- p>,</c-> <c- n>s</c-><c- p>)</c-></code> if <code class="highlight"><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code>, <code class="highlight"><c- n>I</c-></code>, and <code class="highlight"><c- n>S</c-></code> satisfy <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>iterator_reconstructible_range</c-></code>. <code class="highlight"><c- n>r</c-></code> models <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstructible_range</c-></code> if 
       <dl>
        <dd>— <code class="highlight"><c- n>i</c-> <c- o>==</c-> <c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>re_range</c-><c- p>)</c-></code> is <code class="highlight">true</code>, and
        <dd>— <code class="highlight"><c- n>s</c-> <c- o>==</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>re_range</c-><c- p>)</c-></code> is <code class="highlight">true</code>.
       </dl>
      <dd>
       <sup>9.3</sup> — Let <code class="highlight"><c- n>range_it_re_range</c-></code> be the result of <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>>></c-><c- p>,</c-> <c- n>r</c-><c- p>,</c-> <c- n>i</c-><c- p>,</c-> <c- n>s</c-><c- p>)</c-></code>, if <code class="highlight"><c- n>R</c-></code>, <code class="highlight"><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code>, <code class="highlight"><c- n>I</c-></code>, and <code class="highlight"><c- n>S</c-></code> satisfy <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>range_iterator_reconstructible_range</c-></code>. Then <code class="highlight"><c- n>range_it_re_range</c-></code> models <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>range_iterator_reconstructible_range</c-></code> if 
       <dl>
        <dd>— <code class="highlight"><c- n>i</c-> <c- o>==</c-> <c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>range_it_re_range</c-><c- p>)</c-></code> is <code class="highlight">true</code>, and
        <dd>— <code class="highlight"><c- n>s</c-> <c- o>==</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>range_it_re_range</c-><c- p>)</c-></code> is <code class="highlight">true</code>.
       </dl>
     </dl>
     <p>[ Note: If an iterator and a sentinel is passed in that does not come directly from a <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>begin</c-></code> or <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>end</c-></code> expression, then the range of the reconstructed range matches the given iterator and sentinel so long as it is appropriately related. — end Note ]</p>
    </ins>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.4" id="wording-specification-reconstruct_cpo"><span class="secno">6.3.4. </span><span class="content">Insert a new sub-clause "§24.3.13 <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-></code> [<strong>range.prim.recons</strong>]", after "§24.3.12 <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>cdata</c-></code> [<a href="https://eel.is/c++draft/range.prim.cdata"><b>range.prim.cdata</b></a>]":</span><a class="self-link" href="#wording-specification-reconstruct_cpo"></a></h4>
   <blockquote>
    <ins>
     <p><b>24.3.12</b>     <b><code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-></code></b> <span style="float: right">[<b>range.prim.recons</b>]</span></p>
     <p><sup>1</sup> The name <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-></code> denotes a <a href="https://eel.is/c++draft/customization.point.object">customization point object</a>.</p>
     <p><sup>2</sup> The expression <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>I</c-><c- p>,</c-> <c- n>S</c-><c- p>)</c-></code> for some sub-expressions <code class="highlight"><c- n>I</c-></code> and <code class="highlight"><c- n>S</c-></code> is expression-equivalent to: </p>
     <dl>
      <dd><sup>(2.1)</sup> <code class="highlight"><c- n>reconstruct</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>I</c-><c- p>)</c-><c- o>></c-><c- p>(</c-><c- n>I</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>S</c-><c- p>)</c-><c- o>></c-><c- p>(</c-><c- n>S</c-><c- p>))</c-></code> if either <code class="highlight"><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>I</c-><c- p>)</c-><c- o>></c-></code> or <code class="highlight"><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>S</c-><c- p>)</c-><c- o>></c-></code> are class or enumeration types, it is a valid expression, and both <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>I</c-><c- p>)</c-></code> and <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>S</c-><c- p>)</c-></code> model <code class="highlight"><c- n>iterator_reconstructible_range</c-></code>.
      <dd><sup>(2.2)</sup> Otherwise, <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-><c- o>&lt;</c-><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>I</c-><c- p>)</c-><c- o>></c-><c- p>,</c-> <c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>S</c-><c- p>)</c-><c- o>>></c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>I</c-><c- p>)</c-><c- o>></c-><c- p>(</c-><c- n>I</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>S</c-><c- p>)</c-><c- o>></c-><c- p>(</c-><c- n>S</c-><c- p>))</c-></code> if it is a valid expression.
      <dd><sup>(2.3)</sup> Otherwise, <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>I</c-><c- p>,</c-> <c- n>S</c-><c- p>)</c-></code> is ill-formed.
     </dl>
     <p></p>
     <p><sup>3</sup> The expression <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>I</c-><c- p>,</c-> <c- n>S</c-><c- p>)</c-></code> for some type <code class="highlight"><c- n>R</c-></code> and some sub-expressions <code class="highlight"><c- n>I</c-></code> and <code class="highlight"><c- n>S</c-></code> is expression-equivalent to: </p>
     <dl>
      <dd><sup>(2.1)</sup> <code class="highlight"><c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>I</c-><c- p>)</c-><c- o>></c-><c- p>(</c-><c- n>I</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>S</c-><c- p>)</c-><c- o>></c-><c- p>(</c-><c- n>S</c-><c- p>))</c-></code> if it is a valid expression and <code class="highlight"><c- n>R</c-></code>, <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>I</c-><c- p>)</c-></code>, and <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>S</c-><c- p>)</c-></code> model <code class="highlight"><c- n>reconstructible_range</c-></code>.
      <dd><sup>(2.2)</sup> Otherwise, <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>I</c-><c- p>)</c-><c- o>></c-><c- p>(</c-><c- n>I</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>S</c-><c- p>)</c-><c- o>></c-><c- p>(</c-><c- n>S</c-><c- p>))</c-></code>.
     </dl>
     <p></p>
     <p><sup>4</sup> The expression <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>SR</c-><c- p>,</c-> <c- n>I</c-><c- p>,</c-> <c- n>S</c-><c- p>)</c-></code> for some type <code class="highlight"><c- n>R</c-></code>, and some sub-expressions <code class="highlight"><c- n>SR</c-></code>, <code class="highlight"><c- n>I</c-></code>, and <code class="highlight"><c- n>S</c-></code> is expression-equivalent to: </p>
     <dl>
      <dd><sup>(2.1)</sup> <code class="highlight"><c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>SR</c-><c- p>)</c-><c- o>></c-><c- p>(</c-><c- n>SR</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>I</c-><c- p>)</c-><c- o>></c-><c- p>(</c-><c- n>I</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>S</c-><c- p>)</c-><c- o>></c-><c- p>(</c-><c- n>S</c-><c- p>))</c-></code> if it is a valid expression and <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>SR</c-><c- p>)</c-></code>, <code class="highlight"><c- n>R</c-></code>, <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>I</c-><c- p>)</c-></code>, and <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>S</c-><c- p>)</c-></code> model <code class="highlight"><c- n>range_iterator_reconstructible_range</c-></code>.
      <dd><sup>(2.2)</sup> Otherwise, <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>R</c-><c- o>></c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>I</c-><c- p>)</c-><c- o>></c-><c- p>(</c-><c- n>I</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>forward</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>S</c-><c- p>)</c-><c- o>></c-><c- p>(</c-><c- n>S</c-><c- p>))</c-></code>.
     </dl>
     <p></p>
    </ins>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.5" id="wording-specification-string_view_synopsis"><span class="secno">6.3.5. </span><span class="content">Add to "§21.4.3.1 <code class="highlight"><c- n>General</c-></code>" [<a href="eel.is/c++draft/string.view#template.general">string.view.template.general</a>] a <code class="highlight"><c- k>friend</c-></code> function ADL extension point for <code class="highlight"><c- n>basic_string_view</c-></code>:</span><a class="self-link" href="#wording-specification-string_view_synopsis"></a></h4>
   <blockquote>
    <ins>
<pre class="language-cpp highlight">	<c- c1>// [string.view.reconstruct]</c->
	<c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>It</c-><c- p>,</c-> <c- k>class</c-> <c- nc>End</c-><c- o>></c->
		<c- k>friend</c-> <c- k>constexpr</c-> <c- n>basic_string_view</c->
		<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>basic_string_view</c-><c- o>></c->
			<c- n>It</c-> <c- n>first</c-><c- p>,</c-> <c- n>End</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
</pre>
    </ins>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.6" id="wording-specification-string_view"><span class="secno">6.3.6. </span><span class="content">Add a new subclause "§21.4.��� <code class="highlight"><c- n>Range</c-> <c- n>Reconstruction</c-></code>" [string.view.reconstruct] in §21.4:</span><a class="self-link" href="#wording-specification-string_view"></a></h4>
   <blockquote>
    <ins>
     <p><b>21.4.���</b>     <b>Range Reconstruction</b> <span style="float: right">[<b>string.view.reconstruct</b>]</span></p>
<pre class="language-cpp highlight">	<c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>It</c-><c- p>,</c-> <c- k>class</c-> <c- nc>End</c-><c- o>></c->
		<c- k>friend</c-> <c- k>constexpr</c-> <c- n>basic_string_view</c->
		<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>basic_string_view</c-><c- o>></c->
			<c- n>It</c-> <c- n>first</c-><c- p>,</c-> <c- n>End</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
</pre>
     <p><sup>1</sup> <i>Constraints:</i> Let <code class="highlight"><c- n>U</c-></code> be <code class="highlight"><c- n>remove_reference_t</c-><c- o>&lt;</c-><c- n>iter_reference_t</c-><c- o>&lt;</c-><c- n>It</c-><c- o>>></c-></code>. </p>
     <dl>
      <dd><sup>(1.1)</sup> — <code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>U</c-><c- p>(</c-><c- o>*</c-><c- p>)[],</c-> <c- k>const</c-> <c- n>value_type</c-><c- p>(</c-><c- o>*</c-><c- p>)[]</c-><c- o>></c-></code> is <code class="highlight">true</code>. [<i>Note</i>: The intent is to allow only qualification conversions of the iterator reference type to element_type. — <i>end note</i>]
      <dd><sup>(1.2)</sup> — <code class="highlight"><c- n>It</c-></code> models <code class="highlight"><c- n>contiguous_iterator</c-></code>.
      <dd><sup>(1.3)</sup> — <code class="highlight"><c- n>End</c-></code> models <code class="highlight"><c- n>sized_sentinel_for</c-><c- o>&lt;</c-><c- n>It</c-><c- o>></c-></code>.
     </dl>
     <p></p>
     <p><sup>2</sup> <i>Returns:</i> <code class="highlight"><c- n>basic_string_view</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>first</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>last</c-><c- p>))</c-></code>.</p>
    </ins>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.7" id="wording-specification-span_synopsis"><span class="secno">6.3.7. </span><span class="content">Add to "§22.7.3.1 <code class="highlight"><c- n>Overview</c-></code>" [<a href="http://eel.is/c++draft/span.overview">span.overview</a>] a <code class="highlight"><c- k>friend</c-></code> function ADL extension point for <code class="highlight"><c- n>span</c-></code>:</span><a class="self-link" href="#wording-specification-span_synopsis"></a></h4>
   <blockquote>
    <ins>
<pre class="language-cpp highlight">	<c- c1>// [span.reconstruct]</c->
	<c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>It</c-><c- p>,</c-> <c- k>class</c-> <c- nc>End</c-><c- o>></c->
		<c- k>friend</c-> <c- k>constexpr</c-> <c- k>auto</c->
		<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>span</c-><c- o>></c-><c- p>,</c-> <c- n>It</c-> <c- n>first</c-><c- p>,</c-> <c- n>End</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
</pre>
    </ins>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.8" id="wording-specification-span"><span class="secno">6.3.8. </span><span class="content">Add a new subclause "§22.7.3.���� <code class="highlight"><c- n>Range</c-> <c- n>Reconstruction</c-></code>" [span.reconstruct] in §22.7.3:</span><a class="self-link" href="#wording-specification-span"></a></h4>
   <blockquote>
    <ins>
     <p><b>22.7.3.����</b>     <b>Range Reconstruction</b> <span style="float: right">[<b>span.reconstruct</b>]</span></p>
<pre class="language-cpp highlight">	<c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>It</c-><c- p>,</c-> <c- k>class</c-> <c- nc>End</c-><c- o>></c->
		<c- k>friend</c-> <c- k>constexpr</c-> <c- k>auto</c->
		<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>span</c-><c- o>></c-><c- p>,</c-> <c- n>It</c-> <c- n>first</c-><c- p>,</c-> <c- n>End</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
</pre>
     <p><sup>1</sup> <i>Constraints:</i> Let <code class="highlight"><c- n>U</c-></code> be <code class="highlight"><c- n>remove_reference_t</c-><c- o>&lt;</c-><c- n>iter_reference_t</c-><c- o>&lt;</c-><c- n>It</c-><c- o>>></c-></code>. </p>
     <dl>
      <dd><sup>(1.1)</sup> — <code class="highlight"><c- n>is_convertible_v</c-><c- o>&lt;</c-><c- n>U</c-><c- p>(</c-><c- o>*</c-><c- p>)[],</c-> <c- n>element_type</c-><c- p>(</c-><c- o>*</c-><c- p>)[]</c-><c- o>></c-></code> is <code class="highlight">true</code>. [<i>Note</i>: The intent is to allow only qualification conversions of the iterator reference type to element_type. — <i>end note</i>]
      <dd><sup>(1.2)</sup> — <code class="highlight"><c- n>It</c-></code> models <code class="highlight"><c- n>contiguous_iterator</c-></code>.
      <dd><sup>(1.3)</sup> — <code class="highlight"><c- n>End</c-></code> models <code class="highlight"><c- n>sized_sentinel_for</c-><c- o>&lt;</c-><c- n>It</c-><c- o>></c-></code>.
     </dl>
     <p></p>
     <p><sup>2</sup> <i>Returns:</i> <code class="highlight"><c- n>span</c-><c- o>&lt;</c-><c- n>ElementType</c-><c- o>></c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>first</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>last</c-><c- p>))</c-></code> or a <code class="highlight"><c- n>span</c-></code> of static extent using <code class="highlight"><c- n>first</c-></code> and <code class="highlight"><c- n>last</c-></code>. See <em>Remarks</em>.</p>
     <p><sup>3</sup> Remarks: The return type may be promoted to a <code class="highlight"><c- n>span</c-></code> with a static extent if the implementation is capable of deriving such information from the given iterator and sentinel. </p>
    </ins>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.9" id="wording-specification-subrange_synopsis"><span class="secno">6.3.9. </span><span class="content">Add to "§24.5.4.1 <code class="highlight"><c- n>General</c-></code>" [<a href="http://eel.is/c++draft/range.subrange.general">range.subrange.general</a>] a <code class="highlight"><c- k>friend</c-></code> function ADL extension point for <code class="highlight"><c- n>subrange</c-></code>:</span><a class="self-link" href="#wording-specification-subrange_synopsis"></a></h4>
   <blockquote>
    <ins>
<pre class="language-cpp highlight">	<c- k>friend</c-> <c- k>constexpr</c-> <c- n>subrange</c->
	<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>subrange</c-><c- o>></c-><c- p>,</c-> <c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>(</c-><c- n>see</c-><c- o>-</c-><c- n>below</c-><c- p>);</c->

	<c- k>friend</c-> <c- k>constexpr</c-> <c- k>auto</c->
	<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>subrange</c-><c- o>></c-><c- p>,</c-> <c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>(</c-><c- n>see</c-><c- o>-</c-><c- n>below</c-><c- p>);</c->
</pre>
    </ins>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.10" id="wording-specification-subrange"><span class="secno">6.3.10. </span><span class="content">Add a new subclause "§24.5.4.���� <code class="highlight"><c- n>Range</c-> <c- n>Reconstruction</c-></code>" [range.subrange.reconstruct] in §24.5.4:</span><a class="self-link" href="#wording-specification-subrange"></a></h4>
   <blockquote>
    <ins>
     <p><b>22.7.3.����</b>     <b>Range Reconstruction</b> <span style="float: right">[<b>range.subrange.reconstruct</b>]</span></p>
<pre class="language-cpp highlight">	<c- k>friend</c-> <c- k>constexpr</c-> <c- n>subrange</c->
	<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>subrange</c-><c- o>></c-><c- p>,</c-> <c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>(</c-><c- n>see</c-><c- o>-</c-><c- n>below</c-><c- p>);</c->
</pre>
     <p><sup>1</sup> <i>Returns:</i> <code class="highlight"><c- n>subrange</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>first</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>last</c-><c- p>))</c-></code>.</p>
     <p><sup>2</sup> <i>Throws:</i> Anything from evaluating the <i>Returns</i>. Otherwise, nothing.</p>
<pre class="language-cpp highlight">	<c- k>friend</c-> <c- k>constexpr</c-> <c- k>auto</c->
	<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>subrange</c-><c- o>></c-><c- p>,</c-> <c- n>I</c-> <c- n>first</c-><c- p>,</c-> <c- n>I</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>(</c-><c- n>see</c-><c- o>-</c-><c- n>below</c-><c- p>);</c->
</pre>
     <p><sup>3</sup> <i>Returns:</i> <code class="highlight"><c- n>subrange</c-><c- o>&lt;</c-><c- n>I</c-><c- o>></c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>first</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>last</c-><c- p>))</c-></code>.</p>
     <p><sup>4</sup> <i>Throws:</i> Anything from evaluating the <i>Returns</i>. Otherwise, nothing.</p>
    </ins>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.11" id="wording-specification-iota_view_synopsis"><span class="secno">6.3.11. </span><span class="content">Add to "§24.6.4.2 Class template <code class="highlight"><c- n>iota_view</c-></code>" [<a href="http://eel.is/c++draft/range.iota">range.iota</a>] a <code class="highlight"><c- k>friend</c-></code> function ADL extension point for <code class="highlight"><c- n>iota_view</c-></code>:</span><a class="self-link" href="#wording-specification-iota_view_synopsis"></a></h4>
   <blockquote>
    <ins>
<pre class="language-cpp highlight">	<c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>S</c-><c- o>></c->
		<c- k>friend</c-> <c- k>constexpr</c-> <c- n>iota_view</c->
		<c- n>reconstruct</c-><c- p>(</c-><c- n>iterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>(</c-><c- n>see</c-><c- o>-</c-><c- n>below</c-><c- p>);</c->
</pre>
    </ins>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.12" id="#wording-specification-iota_view"><span class="secno">6.3.12. </span><span class="content">Add one new paragraph to "§24.6.4.2 Class template <code class="highlight"><c- n>iota_view</c-></code>" [<a href="http://eel.is/c++draft/range.iota">range.iota</a>]:</span><a class="self-link" href="#%23wording-specification-iota_view"></a></h4>
   <blockquote>
    <ins>
<pre class="language-cpp highlight">	<c- k>template</c-> <c- o>&lt;</c-><c- k>class</c-> <c- nc>S</c-><c- o>></c->
		<c- k>friend</c-> <c- k>constexpr</c-> <c- k>auto</c->
		<c- n>reconstruct</c-><c- p>(</c-><c- n>iterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>S</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>(</c-><c- n>see</c-><c- o>-</c-><c- n>below</c-><c- p>);</c->
</pre>
     <p><sup>��1</sup> <i>Constraints:</i> <code class="highlight"><c- n>S</c-></code> is <i><code class="highlight"><c- n>iterator</c-></code></i> or <code class="highlight"><c- n>S</c-></code> is <i><code class="highlight"><c- n>sentinel</c-></code></i>.</p>
     <p><sup>��2</sup> <i>Effects:</i> Equivalent to: </p>
<pre class="language-cpp highlight"><c- k>if</c-> <c- nf>constexpr</c-> <c- p>(</c-><c- n>same_as</c-><c- o>&lt;</c-><c- n>iterator</c-><c- p>,</c-> <c- n>S</c-><c- o>></c-><c- p>)</c-> <c- p>{</c->
	<c- k>return</c-> <c- n>iota_view</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- o>*</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>first</c-><c- p>)),</c-> <c- k>decltype</c-><c- p>(</c-><c- o>*</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>last</c-><c- p>))</c-><c- o>></c-><c- p>(</c->
		<c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>first</c-><c- p>),</c-> <c- o>*</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>last</c-><c- p>)</c->
	<c- p>);</c->
<c- p>}</c->
<c- k>else</c-> <c- p>{</c->
	<c- k>return</c-> <c- nf>iota_view</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>first</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>last</c-><c- p>));</c->
<c- p>}</c->
</pre>
     <p></p>
     <p><sup>��3</sup> <i>Throws:</i> Anything from evaluating the <i>Effects</i>. Otherwise, nothing.</p>
    </ins>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.13" id="wording-specification-empty_view_synopsis"><span class="secno">6.3.13. </span><span class="content">Add to "§24.6.2.2 Class template <code class="highlight"><c- n>empty_view</c-></code>" [<a href="http://eel.is/c++draft/range.iota">range.empty.view</a>] a <code class="highlight"><c- k>friend</c-></code> function ADL extension point for <code class="highlight"><c- n>empty_view</c-></code>:</span><a class="self-link" href="#wording-specification-empty_view_synopsis"></a></h4>
   <blockquote>
    <ins>
<pre class="language-cpp highlight">	<c- k>friend</c-> <c- k>constexpr</c-> <c- n>empty_view</c->
	<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>empty_view</c-><c- o>></c-><c- p>,</c-> <c- n>T</c-><c- o>*</c-><c- p>,</c-> <c- n>T</c-><c- o>*</c-><c- p>)</c-> <c- k>noexcept</c-> <c- p>{</c->
		<c- k>return</c-> <c- n>empty_view</c-><c- p>{};</c->
	<c- p>}</c->

	<c- k>friend</c-> <c- k>constexpr</c-> <c- n>empty_view</c->
	<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>empty_view</c-><c- o>></c-><c- p>,</c-> <c- n>nullptr_t</c-><c- p>,</c-> <c- n>T</c-><c- o>*</c-><c- p>)</c-> <c- k>noexcept</c-> <c- p>{</c->
		<c- k>return</c-> <c- n>empty_view</c-><c- p>{};</c->
	<c- p>}</c->

	<c- k>friend</c-> <c- k>constexpr</c-> <c- n>empty_view</c->
	<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>empty_view</c-><c- o>></c-><c- p>,</c-> <c- n>T</c-><c- o>*</c-><c- p>,</c-> <c- n>nullptr_t</c-><c- p>)</c-> <c- k>noexcept</c-> <c- p>{</c->
		<c- k>return</c-> <c- n>empty_view</c-><c- p>{};</c->
	<c- p>}</c->

	<c- k>friend</c-> <c- k>constexpr</c-> <c- n>empty_view</c->
	<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>empty_view</c-><c- o>></c-><c- p>,</c-> <c- n>nullptr_t</c-><c- p>,</c-> <c- n>nullptr_t</c-><c- p>)</c-> <c- k>noexcept</c-> <c- p>{</c->
		<c- k>return</c-> <c- n>empty_view</c-><c- p>{};</c->
	<c- p>}</c->
</pre>
    </ins>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.14" id="wording-specification-transform_view_synopsis"><span class="secno">6.3.14. </span><span class="content">Add to "§24.7.6.2 Class template <code class="highlight"><c- n>transform_view</c-></code>" [<a href="http://eel.is/c++draft/range.transform.view">range.transform.view</a>] a <code class="highlight"><c- k>friend</c-></code> function ADL extension point for <code class="highlight"><c- n>transform_view</c-></code>:</span><a class="self-link" href="#wording-specification-transform_view_synopsis"></a></h4>
   <blockquote>
    <ins>
<pre class="language-cpp highlight">	<c- k>template</c-> <c- o>&lt;</c-><c- b>bool</c-> <c- n>iterator_condition</c-><c- p>,</c-> <c- b>bool</c-> <c- n>sentinel_condition</c-><c- o>></c->
		<c- k>friend</c-> <c- k>constexpr</c-> <c- k>auto</c->
		<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>transform_view</c-><c- o>></c-><c- p>,</c-> <c- k>const</c-> <c- n>transform_view</c-> <c- n>original</c->‚
			<c- n>iterator</c-><c- o>&lt;</c-><c- n>iterator_condition</c-><c- o>></c-> <c- n>first</c-><c- p>,</c->
			<c- n>sentinel</c-><c- o>&lt;</c-><c- n>sentinel_condition</c-><c- o>></c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>(</c-><c- n>see</c-><c- o>-</c-><c- n>below</c-><c- p>);</c->

	<c- k>template</c-> <c- o>&lt;</c-><c- b>bool</c-> <c- n>iterator_condition</c-><c- p>,</c-> <c- b>bool</c-> <c- n>sentinel_condition</c-><c- o>></c->
		<c- k>friend</c-> <c- k>constexpr</c-> <c- k>auto</c->
		<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>transform_view</c-><c- o>></c-><c- p>,</c->
			<c- n>transform_view</c-><c- o>&amp;&amp;</c-> <c- n>original</c->‚
			<c- n>iterator</c-><c- o>&lt;</c-><c- n>iterator_condition</c-><c- o>></c-> <c- n>first</c-><c- p>,</c->
			<c- n>sentinel</c-><c- o>&lt;</c-><c- n>sentinel_condition</c-><c- o>></c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>(</c-><c- n>see</c-><c- o>-</c-><c- n>below</c-><c- p>);</c->
</pre>
    </ins>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.15" id="#wording-specification-transform_view"><span class="secno">6.3.15. </span><span class="content">Add new paragraphs to "§24.6.4.2 Class template <code class="highlight"><c- n>transform_view</c-></code>" [<a href="http://eel.is/c++draft/range.transform">range.transform</a>]:</span><a class="self-link" href="#%23wording-specification-transform_view"></a></h4>
   <blockquote>
    <ins>
<pre class="language-cpp highlight">	<c- k>template</c-> <c- o>&lt;</c-><c- b>bool</c-> <c- n>iterator_condition</c-><c- p>,</c-> <c- b>bool</c-> <c- n>sentinel_condition</c-><c- o>></c->
		<c- k>friend</c-> <c- k>constexpr</c-> <c- k>auto</c->
		<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>transform_view</c-><c- o>></c-><c- p>,</c->
			<c- k>const</c-> <c- n>transform_view</c-><c- o>&amp;</c-> <c- n>original</c-><c- p>,</c->
			<c- n>iterator</c-><c- o>&lt;</c-><c- n>iterator_condition</c-><c- o>></c-> <c- n>first</c-><c- p>,</c->
			<c- n>sentinel</c-><c- o>&lt;</c-><c- n>sentinel_condition</c-><c- o>></c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>(</c-><c- n>see</c-><c- o>-</c-><c- n>below</c-><c- p>);</c->
</pre>
     <p><sup>��1</sup> <i>Constraints:</i> <code class="highlight"><c- n>V</c-></code> models <code class="highlight"><c- n>reconstructible_range</c-></code> and <code class="highlight"><c- n>copy_constructible</c-></code>. <code class="highlight"><c- n>F</c-></code> models <code class="highlight"><c- n>copy_constructible</c-></code>.</p>
     <p><sup>��2</sup> <i>Returns:</i> <code class="highlight"><c- n>transform_view</c-><c- p>(</c-><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>first</c-><c- p>).</c-><c- n>current</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>last</c-><c- p>).</c-><c- n>end</c-><c- p>),</c-> <c- o>*</c-><c- n>original</c-><c- p>.</c-><c- n>fun_</c-><c- p>)</c-></code>.</p>
     <p><sup>��3</sup> <i>Throws:</i> Anything from evaluating the <i>Returns</i>. Otherwise, nothing.</p>
<pre class="language-cpp highlight">	<c- k>template</c-> <c- o>&lt;</c-><c- b>bool</c-> <c- n>iterator_condition</c-><c- p>,</c-> <c- b>bool</c-> <c- n>sentinel_condition</c-><c- o>></c->
		<c- k>friend</c-> <c- k>constexpr</c-> <c- k>auto</c->
		<c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type_t</c-><c- o>&lt;</c-><c- n>transform_view</c-><c- o>></c-><c- p>,</c-> <c- n>transform_view</c-><c- o>&amp;&amp;</c-> <c- n>original</c-><c- p>,</c->
			<c- n>iterator</c-><c- o>&lt;</c-><c- n>iterator_condition</c-><c- o>></c-> <c- n>first</c-><c- p>,</c->
			<c- n>sentinel</c-><c- o>&lt;</c-><c- n>sentinel_condition</c-><c- o>></c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>(</c-><c- n>see</c-><c- o>-</c-><c- n>below</c-><c- p>);</c->
</pre>
     <p><sup>��4</sup> <i>Constraints:</i> <code class="highlight"><c- n>V</c-></code> models <code class="highlight"><c- n>reconstructible_range</c-></code>.</p>
     <p><sup>��5</sup> <i>Returns:</i> <code class="highlight"><c- n>transform_view</c-><c- p>(</c-><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>first</c-><c- p>).</c-><c- n>current</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>last</c-><c- p>).</c-><c- n>end</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- o>*</c-><c- n>original</c-><c- p>.</c-><c- n>fun_</c-><c- p>))</c-></code>.</p>
     <p><sup>��6</sup> <i>Throws:</i> Anything from evaluating the <i>Returns</i>. Otherwise, nothing.</p>
    </ins>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.16" id="wording-specification-views_take"><span class="secno">6.3.16. </span><span class="content">Modify "§24.7.7.1 Overview " [<a href="http://eel.is/c++draft/range.take.overview">range.take.overview</a>] for <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>take</c-></code>'s paragraph 2:</span><a class="self-link" href="#wording-specification-views_take"></a></h4>
   <blockquote>
    <p><sup>2</sup> The name <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>take</c-></code> denotes a range adaptor object ([range.adaptor.object]). Let <code class="highlight"><c- n>E</c-></code> and <code class="highlight"><c- n>F</c-></code> be expressions, let <code class="highlight"><c- n>T</c-></code> be <code class="highlight"><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>((</c-><c- n>E</c-><c- p>))</c-><c- o>></c-></code>, and let <code class="highlight"><c- n>D</c-></code> be <code class="highlight"><c- n>range_difference_t</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>((</c-><c- n>E</c-><c- p>))</c-><c- o>></c-></code>. If <code class="highlight"><c- k>decltype</c-><c- p>((</c-><c- n>F</c-><c- p>))</c-></code> does not model <code class="highlight"><c- n>convertible_to</c-><c- o>&lt;</c-><c- n>D</c-><c- o>></c-></code>, <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>take</c-><c- p>(</c-><c- n>E</c-><c- p>,</c-> <c- n>F</c-><c- p>)</c-></code> is ill-formed. Otherwise, the expression views::take(E, F) is expression-equivalent to:</p>
    <del>
     <p></p>
     <dl>
      <dd><sup>(2.1)</sup> — If <code class="highlight"><c- n>T</c-></code> is a specialization of <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>empty_view</c-></code> ([range.empty.view]), then <code class="highlight"><c- p>((</c-><c- b>void</c-><c- p>)</c-> <c- n>F</c-><c- p>,</c-> <c- n>decay</c-><c- o>-</c-><c- n>copy</c-><c- p>(</c-><c- n>E</c-><c- p>))</c-></code>.
      <dd>
       <sup>(2.2)</sup> — Otherwise, if <code class="highlight"><c- n>T</c-></code> models <code class="highlight"><c- n>random_access_range</c-></code> and <code class="highlight"><c- n>sized_range</c-></code> and is 
       <dl>
        <dd><sup>(2.2.1)</sup> — a specialization of <code class="highlight"><c- n>span</c-></code> ([views.span]) where <code class="highlight"><c- n>T</c-><c- o>::</c-><c- n>extent</c-> <c- o>==</c-> <c- n>dynamic_extent</c-></code>,
        <dd><sup>(2.2.2)</sup> — a specialization of <code class="highlight"><c- n>basic_string_view</c-></code> ([string.view]),
        <dd><sup>(2.2.3)</sup> — a specialization of <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>iota_view</c-></code> ([range.iota.view]), or
        <dd><sup>(2.2.4)</sup> — a specialization of <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-></code> ([range.subrange]),
       </dl>
        then <code class="highlight"><c- n>T</c-><c- p>{</c-><c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>E</c-><c- p>),</c-> <c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>E</c-><c- p>)</c-> <c- o>+</c-> <c- n>min</c-><c- o>&lt;</c-><c- n>D</c-><c- o>></c-><c- p>(</c-><c- n>ranges</c-><c- o>::</c-><c- n>size</c-><c- p>(</c-><c- n>E</c-><c- p>),</c-> <c- n>F</c-><c- p>)}</c-></code>, except that <code class="highlight"><c- n>E</c-></code> is evaluated only once.
      <dd><sup>(2.3)</sup> — Otherwise, <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>take_view</c-><c- p>{</c-><c- n>E</c-><c- p>,</c-> <c- n>F</c-><c- p>}</c-></code>.
     </dl>
     <p></p>
    </del>
    <ins>
     <p></p>
     <dl>
      <dd><sup>(2.1)</sup> — If <code class="highlight"><c- n>T</c-></code> is a specialization of <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>empty_view</c-></code> ([range.empty.view]), then <code class="highlight"><c- p>((</c-><c- b>void</c-><c- p>)</c-> <c- n>F</c-><c- p>,</c-> <c- n>decay</c-><c- o>-</c-><c- n>copy</c-><c- p>(</c-><c- n>E</c-><c- p>))</c-></code>.
      <dd><sup>(2.2)</sup> — Otherwise, if <code class="highlight"><c- n>T</c-></code> models both <code class="highlight"><c- n>random_access_range</c-></code> and <code class="highlight"><c- n>sized_range</c-></code>, and, <code class="highlight"><c- n>T</c-></code>, <code class="highlight"><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code>, <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code>, and <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> model <code class="highlight"><c- n>range_iterator_reconstructible_range</c-></code>, then <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>,</c-> <c- n>E</c-><c- p>,</c-> <c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>E</c-><c- p>),</c-> <c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>E</c-><c- p>)</c-> <c- o>+</c-> <c- n>min</c-><c- o>&lt;</c-><c- n>D</c-><c- o>></c-><c- p>(</c-><c- n>ranges</c-><c- o>::</c-><c- n>size</c-><c- p>(</c-><c- n>E</c-><c- p>),</c-> <c- n>F</c-><c- p>))</c-></code>, except that <code class="highlight"><c- n>E</c-></code> is evaluated only once.
      <dd><sup>(2.3)</sup> — Otherwise, <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>take_view</c-><c- p>{</c-><c- n>E</c-><c- p>,</c-> <c- n>F</c-><c- p>}</c-></code>.
     </dl>
     <p></p>
    </ins>
    <p></p>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.17" id="wording-specification-views_drop"><span class="secno">6.3.17. </span><span class="content">Modify "§24.7.9.1 Overview " [<a href="http://eel.is/c++draft/range.drop.overview">range.drop.overview</a>] for <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>drop</c-></code>'s paragraph 2:</span><a class="self-link" href="#wording-specification-views_drop"></a></h4>
   <blockquote>
    <p><sup>2</sup> The name <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>drop</c-></code> denotes a range adaptor object ([range.adaptor.object]). Let <code class="highlight"><c- n>E</c-></code> and <code class="highlight"><c- n>F</c-></code> be expressions, let <code class="highlight"><c- n>T</c-></code> be <code class="highlight"><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>((</c-><c- n>E</c-><c- p>))</c-><c- o>></c-></code>, and let <code class="highlight"><c- n>D</c-></code> be <code class="highlight"><c- n>range_difference_t</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>((</c-><c- n>E</c-><c- p>))</c-><c- o>></c-></code>. If <code class="highlight"><c- k>decltype</c-><c- p>((</c-><c- n>F</c-><c- p>))</c-></code> does not model <code class="highlight"><c- n>convertible_to</c-><c- o>&lt;</c-><c- n>D</c-><c- o>></c-></code>, <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>drop</c-><c- p>(</c-><c- n>E</c-><c- p>,</c-> <c- n>F</c-><c- p>)</c-></code> is ill-formed.
Otherwise, the expression <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>drop</c-><c- p>(</c-><c- n>E</c-><c- p>,</c-> <c- n>F</c-><c- p>)</c-></code> is expression-equivalent to:</p>
    <del>
     <p></p>
     <dl>
      <dd><sup>(2.1)</sup> — If <code class="highlight"><c- n>T</c-></code> is a specialization of <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>empty_view</c-></code> ([range.empty.view]), then <code class="highlight"><c- p>((</c-><c- b>void</c-><c- p>)</c-> <c- n>F</c-><c- p>,</c-> <c- n>decay</c-><c- o>-</c-><c- n>copy</c-><c- p>(</c-><c- n>E</c-><c- p>))</c-></code>.
      <dd>
       <sup>(2.2)</sup> — Otherwise, if <code class="highlight"><c- n>T</c-></code> models <code class="highlight"><c- n>random_access_range</c-></code> and <code class="highlight"><c- n>sized_range</c-></code> and is 
       <dl>
        <dd><sup>(2.2.1)</sup> — a specialization of <code class="highlight"><c- n>span</c-></code> ([views.span]) where <code class="highlight"><c- n>T</c-><c- o>::</c-><c- n>extent</c-> <c- o>==</c-> <c- n>dynamic_extent</c-></code>,
        <dd><sup>(2.2.2)</sup> — a specialization of <code class="highlight"><c- n>basic_string_view</c-></code> ([string.view]),
        <dd><sup>(2.2.3)</sup> — a specialization of <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>iota_view</c-></code> ([range.iota.view]), or
        <dd><sup>(2.2.4)</sup> — a specialization of <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-></code> ([range.subrange]),
       </dl>
        then <code class="highlight"><c- n>T</c-><c- p>{</c-><c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>E</c-><c- p>)</c-> <c- o>+</c-> <c- n>min</c-><c- o>&lt;</c-><c- n>D</c-><c- o>></c-><c- p>(</c-><c- n>ranges</c-><c- o>::</c-><c- n>size</c-><c- p>(</c-><c- n>E</c-><c- p>),</c-> <c- n>F</c-><c- p>),</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>E</c-><c- p>)}</c-></code>, except that <code class="highlight"><c- n>E</c-></code> is evaluated only once.
      <dd><sup>(2.3)</sup> — Otherwise, <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>drop_view</c-><c- p>{</c-><c- n>E</c-><c- p>,</c-> <c- n>F</c-><c- p>}</c-></code>.
     </dl>
     <p></p>
    </del>
    <ins>
     <p></p>
     <dl>
      <dd><sup>(2.1)</sup> — If <code class="highlight"><c- n>T</c-></code> is a specialization of <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>empty_view</c-></code> ([range.empty.view]), then <code class="highlight"><c- p>((</c-><c- b>void</c-><c- p>)</c-> <c- n>F</c-><c- p>,</c-> <c- n>decay</c-><c- o>-</c-><c- n>copy</c-><c- p>(</c-><c- n>E</c-><c- p>))</c-></code>.
      <dd><sup>(2.2)</sup> — Otherwise, if <code class="highlight"><c- n>T</c-></code> models both <code class="highlight"><c- n>random_access_range</c-></code> and <code class="highlight"><c- n>sized_range</c-></code>, and, <code class="highlight"><c- n>T</c-></code>, <code class="highlight"><c- n>remove_cvref_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code>, <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code>, and <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>sentinel_t</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-></code> model <code class="highlight"><c- n>range_iterator_reconstructible_range</c-></code>, then <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>T</c-><c- o>></c-><c- p>,</c-> <c- n>E</c-><c- p>,</c-> <c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>E</c-><c- p>)</c-> <c- o>+</c-> <c- n>min</c-><c- o>&lt;</c-><c- n>D</c-><c- o>></c-><c- p>(</c-><c- n>ranges</c-><c- o>::</c-><c- n>size</c-><c- p>(</c-><c- n>E</c-><c- p>),</c-> <c- n>F</c-><c- p>),</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>E</c-><c- p>))</c-></code>, except that <code class="highlight"><c- n>E</c-></code> is evaluated only once.
      <dd><sup>(2.3)</sup> — Otherwise, <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>drop_view</c-><c- p>{</c-><c- n>E</c-><c- p>,</c-> <c- n>F</c-><c- p>}</c-></code>.
     </dl>
     <p></p>
    </ins>
    <p></p>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.18" id="wording-specification-views_split_find_next"><span class="secno">6.3.18. </span><span class="content">Modify "§24.7.14.2 Class template <code class="highlight"><c- n>split_</c->­<c- n>view</c-></code>" [<a href="http://eel.is/c++draft/range.split.view">range.split.view</a>] for <code class="highlight"><c- n>split_view</c-></code>'s <i><code class="highlight"><c- n>find</c-><c- o>-</c-><c- n>next</c-></code></i> exposition-only function:</span><a class="self-link" href="#wording-specification-views_split_find_next"></a></h4>
   <blockquote>
    <del>
<pre class="language-cpp highlight">	<c- k>constexpr</c-> <c- n>subrange</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c-> <c- n>find</c-><c- o>-</c-><c- n>next</c-><c- p>(</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-><c- p>);</c-> <c- c1>// exposition only</c->
</pre>
    </del>
    <ins>
<pre class="language-cpp highlight">	<c- k>using</c-> <c- n>re_type</c-> <c- o>=</c-> <c- n>reconstruct_t</c-><c- o>&lt;</c-><c- n>V</c-><c- p>,</c-> <c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-><c- p>,</c-> <c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c-><c- p>;</c-> <c- c1>// exposition only</c->
	<c- k>constexpr</c-> <c- n>re_type</c-> <c- n>find</c-><c- o>-</c-><c- n>next</c-><c- p>(</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-><c- p>);</c-> <c- c1>// exposition only</c->
</pre>
    </ins>
   </blockquote>
   <h4 class="heading settled" data-level="6.3.19" id="wording-specification-split_iterator_value_type"><span class="secno">6.3.19. </span><span class="content">Modify "§24.7.14.3 Class <code class="highlight"><c- n>split_</c->­<c- n>view</c->​<c- o>::</c->​<c- n>iterator</c-></code>" [<a href="http://eel.is/c++draft/range.split.iterator">range.split.iterator</a>] for <code class="highlight"><c- n>split_view</c-><c- o>&lt;</c->…<c- o>>::</c-><c- n>iterator</c-></code>'s <code class="highlight"><c- n>value_type</c-></code> in the Synopsis:</span><a class="self-link" href="#wording-specification-split_iterator_value_type"></a></h4>
   <del>
<pre class="language-cpp highlight"><c- k>template</c-> <c- o>&lt;</c->…<c- o>></c->
	<c- k>requires</c-> …
<c- k>class</c-> <c- nc>split_view</c-><c- o>&lt;</c->…<c- o>>::</c-><c- n>iterator</c-> <c- p>{</c->
<c- k>private</c-><c- o>:</c->
	<c- c1>// ...</c->
	<c- n>subrange</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c-> <c- n>next_</c-> <c- o>=</c-> <c- n>subrange</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c-><c- p>();</c->  <c- c1>// exposition only</c->
<c- k>public</c-><c- o>:</c->
	<c- c1>// ...</c->
	<c- k>using</c-> <c- n>value_type</c-> <c- o>=</c-> <c- n>subrange</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c-><c- p>;</c->
	<c- c1>// ...</c->
<c- p>}</c->
</pre>
   </del>
   <ins>
<pre class="language-cpp highlight"><c- k>template</c-> <c- o>&lt;</c->…<c- o>></c->
	<c- k>requires</c-> …
<c- k>class</c-> <c- nc>split_view</c-><c- o>&lt;</c->…<c- o>>::</c-><c- n>iterator</c-> <c- p>{</c->
<c- k>private</c-><c- o>:</c->
	<c- c1>// ...</c->
	<c- n>re_type</c-> <c- n>next_</c-> <c- o>=</c-> <c- n>re_type</c-><c- p>();</c->  <c- c1>// exposition only</c->
<c- k>public</c-><c- o>:</c->
	<c- c1>// ...</c->
	<c- k>using</c-> <c- n>value_type</c-> <c- o>=</c-> <c- n>re_type</c-><c- p>;</c->
	<c- c1>// ...</c->
<c- p>}</c->
</pre>
   </ins>
   <h4 class="heading settled" data-level="6.3.20" id="wording-specification-views_split"><span class="secno">6.3.20. </span><span class="content">Modify "§24.7.14.2 Class template <code class="highlight"><c- n>split_</c->­<c- n>view</c-></code>" [<a href="http://eel.is/c++draft/range.split.view">range.split.view</a>] for <code class="highlight"><c- n>split_view</c-></code>'s Overview and paragraph 5:</span><a class="self-link" href="#wording-specification-views_split"></a></h4>
   <blockquote>
    <div class="wording-section">
     <div class="wording-numbered-5">
      <del>
<pre class="language-cpp highlight"><c- k>constexpr</c-> <c- n>subrange</c-><c- o>&lt;</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>>></c-> <c- n>find</c-><c- o>-</c-><c- n>next</c-><c- p>(</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-> <c- n>it</c-><c- p>);</c-> <c- c1>// exposition only</c->
</pre>
       <p>_Effects_: Equivalent to:</p>
<pre class="language-cpp highlight"><c- k>auto</c-> <c- p>[</c-><c- n>b</c-><c- p>,</c-> <c- n>e</c-><c- p>]</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>search</c-><c- p>(</c-><c- n>subrange</c-><c- p>(</c-><c- n>it</c-><c- p>,</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>base_</c-><c- p>)),</c-> <c- n>pattern_</c-><c- p>);</c->
<c- k>if</c-> <c- p>(</c-><c- n>b</c-> <c- o>!=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>base_</c-><c- p>)</c-> <c- o>&amp;&amp;</c-> <c- n>ranges</c-><c- o>::</c-><c- n>empty</c-><c- p>(</c-><c- n>pattern_</c-><c- p>))</c-> <c- p>{</c->
  <c- o>++</c-><c- n>b</c-><c- p>;</c->
  <c- o>++</c-><c- n>e</c-><c- p>;</c->
<c- p>}</c->
<c- k>return</c-> <c- p>{</c-><c- n>b</c-><c- p>,</c-> <c- n>e</c-><c- p>};</c->
</pre>
      </del>
      <ins>
<pre class="language-cpp highlight"><c- k>constexpr</c-> <c- n>re_type</c-> <c- n>find</c-><c- o>-</c-><c- n>next</c-><c- p>(</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-> <c- n>it</c-><c- p>);</c-> <c- c1>// exposition only</c->
</pre>
       <p>_Effects_: Equivalent to:</p>
<pre class="language-cpp highlight"><c- k>auto</c-> <c- p>[</c-><c- n>b</c-><c- p>,</c-> <c- n>e</c-><c- p>]</c-> <c- o>=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>search</c-><c- p>(</c-><c- n>subrange</c-><c- p>(</c-><c- n>it</c-><c- p>,</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>base_</c-><c- p>)),</c-> <c- n>pattern_</c-><c- p>);</c->
<c- k>if</c-> <c- p>(</c-><c- n>b</c-> <c- o>!=</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>base_</c-><c- p>)</c-> <c- o>&amp;&amp;</c-> <c- n>ranges</c-><c- o>::</c-><c- n>empty</c-><c- p>(</c-><c- n>pattern_</c-><c- p>))</c-> <c- p>{</c->
  <c- o>++</c-><c- n>b</c-><c- p>;</c->
  <c- o>++</c-><c- n>e</c-><c- p>;</c->
<c- p>}</c->
<c- k>return</c-> <c- n>ranges</c-><c- o>::</c-><c- n>reconstruct</c-><c- p>(</c-><c- n>in_place_type</c-><c- o>&lt;</c-><c- n>V</c-><c- o>></c-><c- p>,</c-> <c- n>b</c-><c- p>,</c-> <c- n>e</c-><c- p>);</c->
</pre>
      </ins>
     </div>
    </div>
   </blockquote>
   <h2 class="heading settled" data-level="7" id="acknowledgements"><span class="secno">7. </span><span class="content">Acknowledgements</span><a class="self-link" href="#acknowledgements"></a></h2>
   <p>Thanks to Corentin Jabot, Christopher DiBella, and Hannes Hauswedell for pointing me to <a data-link-type="biblio" href="#biblio-p1035r7">[p1035r7]</a> and <a data-link-type="biblio" href="#biblio-p1739r4">[p1739r4]</a> to review both papers and combine some of their ideas in here. Thanks to Eric Niebler for prompting me to think of the generic, scalable solution to this problem rather than working on one-off fixes for individuals views.</p>
   <p>Thank you to Oktal, Anointed of ADL, Blessed Among Us, and Morwenn, the ever-watching Code Guardian for suggesting improvements to the current concept form.</p>
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  <h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span><a class="self-link" href="#references"></a></h2>
  <h3 class="no-num no-ref heading settled" id="informative"><span class="content">Informative References</span><a class="self-link" href="#informative"></a></h3>
  <dl>
   <dt id="biblio-blog-views-split">[BLOG-VIEWS-SPLIT]
   <dd>JeanHeyd Meneide. <a href="https://thephd.dev/ranges-split-final-frontier-reconstructible"><cite>views::split: The Final Frontier</cite></a>. December 12&lt;sup>th&lt;/sup>, 2021. URL: <a href="https://thephd.dev/ranges-split-final-frontier-reconstructible">https://thephd.dev/ranges-split-final-frontier-reconstructible</a>
   <dt id="biblio-icuchariterator">[ICUCHARITERATOR]
   <dd>Unicode Consortium; International Components for Unicode. <a href="https://unicode-org.github.io/icu/userguide/strings/characteriterator.html"><cite>CharacterIterator: ICU Documentation</cite></a>. March 22&lt;sup>nd&lt;/sup>, 2021. URL: <a href="https://unicode-org.github.io/icu/userguide/strings/characteriterator.html">https://unicode-org.github.io/icu/userguide/strings/characteriterator.html</a>
   <dt id="biblio-n4835">[N4835]
   <dd>Richard Smith. <a href="https://wg21.link/n4835"><cite>Working Draft, Standard for Programming Language C++</cite></a>. 8 October 2019. URL: <a href="https://wg21.link/n4835">https://wg21.link/n4835</a>
   <dt id="biblio-p0009r9">[P0009R9]
   <dd>H. Carter Edwards, Bryce Adelstein Lelbach, Daniel Sunderland, D. S. Hollman, Christian Trott, Mauro Bianco, Ben Sander, Athanasios Iliopoulos, John Michopoulos, Mark Hoemmen. <a href="https://wg21.link/p0009r9"><cite>mdspan: A Non-Owning Multidimensional Array Reference</cite></a>. 20 January 2019. URL: <a href="https://wg21.link/p0009r9">https://wg21.link/p0009r9</a>
   <dt id="biblio-p1035r7">[P1035R7]
   <dd>Christopher Di Bella, Casey Carter, Corentin Jabot. <a href="https://wg21.link/p1035r7"><cite>Input Range Adaptors</cite></a>. 2 August 2019. URL: <a href="https://wg21.link/p1035r7">https://wg21.link/p1035r7</a>
   <dt id="biblio-p1255r4">[P1255R4]
   <dd>Steve Downey. <a href="https://wg21.link/p1255r4"><cite>A view of 0 or 1 elements: view::maybe</cite></a>. 17 June 2019. URL: <a href="https://wg21.link/p1255r4">https://wg21.link/p1255r4</a>
   <dt id="biblio-p1391r2">[P1391R2]
   <dd>Corentin Jabot. <a href="https://wg21.link/p1391r2"><cite>Range constructor for std::string_view</cite></a>. 17 June 2019. URL: <a href="https://wg21.link/p1391r2">https://wg21.link/p1391r2</a>
   <dt id="biblio-p1394r2">[P1394R2]
   <dd>Corentin Jabot, Casey Carter. <a href="https://wg21.link/p1394r2"><cite>Range constructor for std::span</cite></a>. 17 June 2019. URL: <a href="https://wg21.link/p1394r2">https://wg21.link/p1394r2</a>
   <dt id="biblio-p1629r1">[P1629R1]
   <dd>JeanHeyd Meneide. <a href="https://wg21.link/p1629r1"><cite>Transcoding the world - Standard Text Encoding</cite></a>. 2 March 2020. URL: <a href="https://wg21.link/p1629r1">https://wg21.link/p1629r1</a>
   <dt id="biblio-p1739r4">[P1739R4]
   <dd>Hannes Hauswedell. <a href="https://wg21.link/p1739r4"><cite>Avoid template bloat for safe_ranges in combination with 'subrange-y' view adaptors.</cite></a>. 1 March 2020. URL: <a href="https://wg21.link/p1739r4">https://wg21.link/p1739r4</a>
   <dt id="biblio-p1989r0">[P1989R0]
   <dd>Corentin Jabot. <a href="https://wg21.link/p1989r0"><cite>Range constructor for std::string_view 2: Constrain Harder</cite></a>. 25 November 2019. URL: <a href="https://wg21.link/p1989r0">https://wg21.link/p1989r0</a>
   <dt id="biblio-p2210r2">[P2210R2]
   <dd>Barry Revzin. <a href="https://wg21.link/p2210r2"><cite>Superior String Splitting</cite></a>. 5 March 2021. URL: <a href="https://wg21.link/p2210r2">https://wg21.link/p2210r2</a>
   <dt id="biblio-p2415">[P2415]
   <dd>Barry Revzin; Tim Song. <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2415r0.html"><cite>What is a View?</cite></a>. July 13&lt;sup>th&lt;/sup>, 2021. URL: <a href="http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2415r0.html">http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2021/p2415r0.html</a>
   <dt id="biblio-range-v3">[RANGE-V3]
   <dd>Eric Niebler; Casey Carter. <a href="https://github.com/ericniebler/range-v3"><cite>range-v3</cite></a>. June 11&lt;sup>th&lt;/sup>, 2019. URL: <a href="https://github.com/ericniebler/range-v3">https://github.com/ericniebler/range-v3</a>
   <dt id="biblio-range-v3-1192">[RANGE-V3-1192]
   <dd>ThePhD. <a href="https://github.com/ericniebler/range-v3/issues/1192"><cite>Ranges which take a sentinel should be constructible from {Iterator, Sentinel}</cite></a>. June 11&lt;sup>th&lt;/sup>, 2019. URL: <a href="https://github.com/ericniebler/range-v3/issues/1192">https://github.com/ericniebler/range-v3/issues/1192</a>
   <dt id="biblio-ztdtext">[ZTD.TEXT]
   <dd>JeanHeyd Meneide; Shepherd's Oasis, LLC. <a href="https://ztdtext.readthedocs.io/en/latest/"><cite>ztd.text - A C++ Text Library</cite></a>. November 20&lt;sup>th&lt;/sup>, 2021. URL: <a href="https://ztdtext.readthedocs.io/en/latest/">https://ztdtext.readthedocs.io/en/latest/</a>
  </dl>