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  <title>P1664R3: 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;
	}

	.head img[src*="logos/W3C"] {
		display: block;
		border: solid #1a5e9a;
		border: solid var(--logo-bg);
		border-width: .65rem .7rem .6rem;
		border-radius: .4rem;
		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,
	#subtitle {
		/* #subtitle 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: none;
		border-bottom: 1px solid #707070;
		border-bottom: 1px solid var(--a-normal-underline);
		/* Need a bit of extending for it to look okay */
		padding: 0 1px 0;
		margin: 0 -1px 0;
	}
	a:visited {
		color: #034575;
		color: var(--a-visited-text);
		border-bottom-color: #bbb;
		border-bottom-color: var(--a-visited-underline);
	}

	/* Use distinguishing colors when user is interacting with the link */
	a[href]:focus,
	a[href]:hover {
		background: #f8f8f8;
		background: rgba(75%, 75%, 75%, .25);
		background: var(--a-hover-bg);
		border-bottom-width: 3px;
		margin-bottom: -2px;
	}
	a[href]:active {
		color: #c00;
		color: var(--a-active-text);
		border-color: #c00;
		border-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-top: 0.1rem;
		/* Larger, more consistently-sized click target */
		display: block;
		/* 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: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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    del { background: #fcc; color: #000; text-decoration: line-through; }
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    blockquote ul { background: inherit; }
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    blockquote c-[t] { color: inherit; } /* Literal.String.Single */
    blockquote c-[u] { color: inherit; } /* Literal.String.Double */
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    blockquote c-[sc] { color: inherit; } /* Literal.String.Char */
    blockquote c-[sd] { color: inherit; } /* Literal.String.Doc */
    blockquote c-[se] { color: inherit; } /* Literal.String.Escape */
    blockquote c-[sh] { color: inherit; } /* Literal.String.Heredoc */
    blockquote c-[si] { color: inherit; } /* Literal.String.Interpol */
    blockquote c-[sx] { color: inherit; } /* Literal.String.Other */
    blockquote c-[sr] { color: inherit; } /* Literal.String.Regex */
    blockquote c-[ss] { color: inherit; } /* Literal.String.Symbol */
    blockquote c-[vc] { color: inherit; } /* Name.Variable.Class */
    blockquote c-[vg] { color: inherit; } /* Name.Variable.Global */
    blockquote c-[vi] { color: inherit; } /* Name.Variable.Instance */
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  <meta content="Bikeshed version b94c7e755, updated Fri Feb 19 16:28:59 2021 -0800" name="generator">
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<style>
<pre class=include-raw line-number=-1 path='resources/css/wording.css'></pre></style>
<style>
@media (prefers-color-scheme: dark) {
	ins { background: rgba(0, 49, 0); color: rgba(115, 255, 110); text-decoration: underline; }
	del { background: rgba(49, 0, 0); color: rgb(255, 124, 124); text-decoration: line-through; }
	recent-ins { background: rgba(0, 49, 0); color: rgba(80, 80, 255); text-decoration: underline; }
	recent-del { background: rgba(49, 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, 49, 0); }
	blockquote del .highlight:not(.idl) { background: rgba(49,  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) {
	ins { background: rgba(200, 255, 200); color: rgba(0, 20, 0); text-decoration: underline; }
	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: #707070;
    --a-visited-text: var(--a-normal-text);
    --a-visited-underline: #bbb;
    --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-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%);
        --notesummary-underline: silver;

        --assertion-border: #444;
        --assertion-bg: var(--borderedblock-bg);
        --assertion-text: var(--text);

        --advisement-border: orange;
        --advisement-bg: #222218;
        --advisement-text: var(--text);
        --advisementheading-text: #f84;

        --warning-border: red;
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 <body class="h-entry">
  <div class="head">
   <p data-fill-with="logo"></p>
   <h1 class="p-name no-ref" id="title">P1664R3<br>reconstructible_range - a concept for putting ranges back together</h1>
   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Published Proposal, <time class="dt-updated" datetime="2021-04-15">2021-04-15</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.github.io/_vendor/future_cxx/papers/d1664.html">https://thephd.github.io/_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-r4"><span class="secno">1.1</span> <span class="content">Revision 3 - April 15th, 2021</span></a>
      <li><a href="#changelog-r2"><span class="secno">1.2</span> <span class="content">Revision 2 - January 13th, 2020</span></a>
      <li><a href="#changelog-r1"><span class="secno">1.3</span> <span class="content">Revision 1 - November 24th, 2019</span></a>
      <li><a href="#changelog-r0"><span class="secno">1.4</span> <span class="content">Revision 0 - August, 5th, 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-preservation"><span class="secno">2.1</span> <span class="content">Preservation of Properties</span></a>
      <li><a href="#motivation-compilation"><span class="secno">2.2</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-multiple"><span class="secno">3.1</span> <span class="content">Multiple, Safe Reconstruction Points</span></a>
      <li><a href="#design-all"><span class="secno">3.2</span> <span class="content">Should this apply to all Ranges?</span></a>
      <li><a href="#design-applicable"><span class="secno">3.3</span> <span class="content">Applicability</span></a>
      <li><a href="#design-dual"><span class="secno">3.4</span> <span class="content">Two Concepts</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-library"><span class="secno">6.3</span> <span class="content">Proposed Library Wording</span></a>
     </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-r4"><span class="secno">1.1. </span><span class="content">Revision 3 - April 15th, 2021</span><a class="self-link" href="#changelog-r4"></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="1.2" id="changelog-r2"><span class="secno">1.2. </span><span class="content">Revision 2 - January 13th, 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="1.3" id="changelog-r1"><span class="secno">1.3. </span><span class="content">Revision 1 - November 24th, 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 6th)</p>
    <li data-md>
     <p>Update wording to target <a data-link-type="biblio" href="#biblio-n4835">[n4835]</a>. (November 6th)</p>
    <li data-md>
     <p>Moved by LWG! 🎉 (November 6th)</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="1.4" id="changelog-r0"><span class="secno">1.4. </span><span class="content">Revision 0 - August, 5th, 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>
   <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- 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>name_view</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</c-><c- p>(</c-><c- n>input</c-><c- p>,</c-> <c- n>output</c-><c- p>);</c->
<c- c1>// compiler error here !!</c->
<c- n>std</c-><c- o>::</c-><c- n>u8string_view</c-> <c- n>unprocessed_code_units</c-> 
	<c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>input</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>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>name_view</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</c-><c- p>(</c-><c- n>input</c-><c- p>,</c-> <c- n>output</c-><c- p>);</c->
<c- k>auto</c-> <c- n>unprocessed_code_units</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_code_units</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>std</c-><c- o>::</c-><c- n>span</c-><c- o>&lt;</c-><c- b>char16_t</c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>dynamic_extent</c-><c- o>>::</c-><c- n>iterator</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- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>dynamic_extent</c-><c- o>>::</c-><c- n>iterator</c-><c- o>></c-></code> 
      <td>
<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>name_view</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</c-><c- p>(</c-><c- n>input</c-><c- p>,</c-> <c- n>output</c-><c- p>);</c->
<c- c1>// compiler error here !!</c->
<c- n>std</c-><c- o>::</c-><c- n>u8string_view</c-> <c- n>unprocessed_code_units</c-> 
	<c- o>=</c-> <c- n>encoding_result</c-><c- p>.</c-><c- n>input</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>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>name_view</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</c-><c- p>(</c-><c- n>input</c-><c- p>,</c-> <c- n>output</c-><c- p>);</c->
<c- k>auto</c-> <c- n>unprocessed_code_units</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_code_units</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>. 
   </table>
   <p>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>uRange</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- 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- c1>// ⛔!</c->
		<c- c1>// ... the below errors</c->
		<c- k>return</c-> <c- nf>uRange</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>uRange</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</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>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>uRange</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- p>;</c->
	<c- k>using</c-> <c- n>I</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>Iterator</c-><c- o>&lt;</c-><c- n>uRange</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>Sentinel</c-><c- o>&lt;</c-><c- n>uRange</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="2.1" id="motivation-preservation"><span class="secno">2.1. </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="2.2" id="motivation-compilation"><span class="secno">2.2. </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 (or subrange of 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.</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 2 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>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>remove_reference_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>remove_reference_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>>></c->
<c- k>concept</c-> <c- nc>pair_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- n>ranges</c-><c- o>::</c-><c- n>borrowed_range</c-><c- o>&lt;</c-><c- n>remove_reference_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></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>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>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- 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>Range</c-> <c- o>=</c-> <c- n>remove_reference_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- n>ranges</c-><c- o>::</c-><c- n>borrowed_range</c-><c- o>&lt;</c-><c- n>remove_reference_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></c-> <c- o>&amp;&amp;</c->
	<c- k>requires</c-> <c- p>(</c-><c- n>Range</c-> <c- n>first_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>move</c-><c- p>(</c-><c- n>first_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 begin iterator and end iterator/sentinel. It also provides a concept for allowing a range to be put back together from another range, which may be useful for some types of ranges where more than the iterator and sentinel are required. This allows a developer 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.</p>
   <p>Both concepts require that the type with any references removed model the concept <code class="highlight"><c- n>borrowed_range</c-></code>. This ensures that the validity of the iterators is in fact independent of the lifetime of the range they originate from and that a "reconstructed" range does not depend on the original. We remove reference before performing this check, because all reference types that model <code class="highlight"><c- n>Range</c-></code> also model <code class="highlight"><c- n>borrowed_range</c-></code> and the intent of the proposed changes is narrower: (re)construction is assumed to be in constant time (this typically implies that <code class="highlight"><c- n>R</c-></code> also models <code class="highlight"><c- n>View</c-></code>, but it is sufficient to check <code class="highlight"><c- n>borrowed_range</c-><c- o>&lt;</c-><c- n>remove_reference_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></c-></code>).</p>
   <p>Note that this explicitly excludes types like <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>vector</c-><c- o>&lt;</c-><c- b>int</c-><c- o>></c-> <c- k>const</c-> <c- o>&amp;</c-></code> from being reconstructible.</p>
   <h3 class="heading settled" data-level="3.1" id="design-multiple"><span class="secno">3.1. </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- 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- 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 design, and can aid in providing better static guarantees while decaying gracefully in other situations.</p>
   <h3 class="heading settled" data-level="3.2" id="design-all"><span class="secno">3.2. </span><span class="content">Should this apply to all Ranges?</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 *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.</p>
   <p>Finally, there are ranges which could be reconstructible by just the definition of a constructor that takes iterators or a <code class="highlight"><c- n>subrange</c-></code>. While this was a benefit in that the majority of conforming ranges were reconstructible, it made a situation where someone could write a strange range. For example, consider this alternative implementation of <code class="highlight"><c- n>rng</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-></code>:</p>
<pre class="language-cpp highlight"><c- k>class</c-> <c- nc>pop_front_view</c-> <c- p>{</c->
<c- k>private</c-><c- o>:</c->
	<c- b>int</c-> <c- o>*</c-><c- n>begin_</c-><c- p>,</c-> <c- o>*</c-><c- n>end_</c-><c- p>;</c->

<c- k>public</c-><c- o>:</c->
	<c- n>pop_front_view</c-><c- p>()</c-> <c- o>=</c-> <c- k>default</c-><c- p>;</c->

	<c- n>pop_front_view</c-><c- p>(</c-><c- b>int</c-><c- o>*</c-> <c- n>begin</c-><c- p>,</c-> <c- b>int</c-><c- o>*</c-> <c- n>end</c-><c- p>)</c->
		<c- o>:</c-> <c- n>begin_</c-><c- p>(</c-><c- n>begin</c-><c- o>==</c-><c- n>end</c-><c- o>?</c-><c- nl>begin</c-><c- p>:</c-><c- n>begin</c-><c- o>+</c-><c- mi>1</c-><c- p>),</c-> <c- n>end_</c-><c- p>(</c-><c- n>end</c-><c- p>)</c->
	<c- p>{}</c->

	<c- b>int</c-><c- o>*</c-> <c- n>begin</c-><c- p>()</c-> <c- k>const</c-> <c- p>{</c-> <c- k>return</c-> <c- n>begin_</c-><c- p>;</c-> <c- p>}</c->

	<c- b>int</c-><c- o>*</c-> <c- n>end</c-><c- p>()</c-> <c- k>const</c-> <c- p>{</c-> <c- k>return</c-> <c- n>end_</c-><c- p>;</c-> <c- p>}</c->
<c- p>};</c->
</pre>
   <p>Reconstructing this range using the constructors is a surefire way to have a developer scratching at their head, wondering what is going on. Therefore, rather than require reconstruction through the constructor, we rely instead on an Customization Point Object design instead.</p>
   <h3 class="heading settled" data-level="3.3" id="design-applicable"><span class="secno">3.3. </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 _spirit_ 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="3.4" id="design-dual"><span class="secno">3.4. </span><span class="content">Two Concepts</span><a class="self-link" href="#design-dual"></a></h3>
   <p>By giving these ranges <code class="highlight"><c- n>Iterator</c-><c- p>,</c-> <c- n>Sentinel</c-></code>, and/or <code class="highlight"><c- n>Range</c-></code> reconstruction functions, we can enable a greater degree of interface fidelity without having to resort to <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-></code> for all generic algorithms or similar input/output iterator holders as we have in much of the current <code class="highlight"><c- n>ranges</c-></code> <code class="highlight"><c- o>&lt;</c-><c- n>algorithms</c-><c- o>></c-></code> library.</p>
   <p><code class="highlight"><c- n>reconstruct</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>inplace_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>Sentinel</c-><c- p>)</c-></code> reconstruction is important for building <code class="highlight"><c- n>llvm</c-><c- o>::</c-><c- n>StringRef</c-></code>, <code class="highlight"><c- n>llfio</c-><c- o>::</c-><c- n>span</c-></code>, <code class="highlight"><c- n>kokos</c-><c- o>::</c-><c- n>mdspan</c-></code>, and other types that go into algorithms.</p>
   <p>because one-argument functions can have extremely overloaded meanings. It also produces less compiler boilerplate to achieve the same result of reconstructing the range when one does not have to go through <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>. However, it is important to attempt to move away from the iterator, sentinel model being deployed all the time: <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-></code> offers a single type that can accurately represent the intent and can be fairly easy to constrain overload sets on (most of the time) due to being a single family of types (anyone can check for a the type being a specialization of <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>subrange</c-></code>, whereas iterators span multiple different families of types).</p>
   <p>This paper includes two concepts that cover both reconstructible methods.</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/text/detail/reconstruct.hpp">at the soasis/text repository here</a>, which is mimicking the interface needed for <a data-link-type="biblio" href="#biblio-p1629r1">[p1629r1]</a>.</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 Design, no currently created range or previously made range is permanently affected.</p>
   <p>Furthermore, this is a new and separate concept. 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.</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>pair_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>and, add two new concepts to <a href="http://eel.is/c++draft/range.req">[range.req</a>].</p>
   </ul>
   <p>If <em>borrowed_range</em> is changed to the <code class="highlight"><c- n>borrowed_range</c-></code> concept name, then this entire proposal will rename all its uses of <em>borrowed_range</em>.</p>
   <p>For ease of reading, the necessary portions of other proposal’s wording is duplicated here, with the changes necessary for the application of reconstructible range concepts. Such sections are clearly marked.</p>
   <h3 class="heading settled" data-level="6.3" id="wording-library"><span class="secno">6.3. </span><span class="content">Proposed Library Wording</span><a class="self-link" href="#wording-library"></a></h3>
   <p>Add a feature test macro <code class="highlight"><c- n>__cpp_lib_reconstructible_range</c-></code>.</p>
   <p>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:</p>
   <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> <c- kr> </c-><ins><c- kr>nline</c-> <c- k>constexpr</c-> <c- n> </c-><i><c- n>nspecified</c-> </i><c- n>reconstruct</c-> <c- o>=</c-> <c- n>unspecified</c-><c- p>;</c-> </ins><br> <br> … <br> <br> <c- p>}</c-> <br><c- p>}</c-> </code> </blockquote>
   <p>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:</p>
   <blockquote>
    <ins>
     <sup>8</sup> The concepts <code class="highlight"><c- n>pair_reconstructible_range</c-></code> and <code class="highlight"><c- n>reconstructible_range</c-></code> concepts describe the requirements on ranges that are efficiently constructible from values of their iterator and sentinel types. 
<pre class="language-cpp highlight"><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>remove_reference_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>remove_reference_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>>></c->
<c- k>concept</c-> <c- nc>pair_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- n>ranges</c-><c- o>::</c-><c- n>borrowed_range</c-><c- o>&lt;</c-><c- n>remove_reference_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></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>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>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- 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>Range</c-> <c- o>=</c-> <c- n>remove_reference_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- n>ranges</c-><c- o>::</c-><c- n>borrowed_range</c-><c- o>&lt;</c-><c- n>remove_reference_t</c-><c- o>&lt;</c-><c- n>R</c-><c- o>>></c-> <c- o>&amp;&amp;</c->
	<c- k>requires</c-> <c- p>(</c-><c- n>Range</c-> <c- n>first_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>move</c-><c- p>(</c-><c- n>first_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>.</p>
     <dl>
      <dd>
       <sup>9.1</sup> — Let <code class="highlight"><c- n>re</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>R</c-><c- o>>></c-><c- p>,</c-> <c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>r</c-><c- p>),</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>r</c-><c- p>))</c-></code> if such an expression is well-formed. <code class="highlight"><c- n>r</c-></code> models <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>pair_reconstructible_range</c-></code> if 
       <dl>
        <dd>— <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>r</c-><c- p>)</c-> <c- o>==</c-> <c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>re</c-><c- p>)</c-></code> is true, and
        <dd>— <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>r</c-><c- p>)</c-> <c- o>==</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>re</c-><c- p>)</c-></code> is true.
       </dl>
      <dd>
       <sup>9.2</sup> — Let <code class="highlight"><c- n>sub_re</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>R</c-><c- o>>></c-><c- p>,</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>r</c-><c- p>))</c-></code>, if such an expression is well-formed. Then <code class="highlight"><c- n>sub_re</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>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>r</c-><c- p>)</c-> <c- o>==</c-> <c- n>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>sub_re</c-><c- p>)</c-></code> is true, and
        <dd>— <code class="highlight"><c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>r</c-><c- p>)</c-> <c- o>==</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>sub_re</c-><c- p>)</c-></code> is true.
       </dl>
     </dl>
    </ins>
   </blockquote>
   <p>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>]":</p>
   <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>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>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>move</c-><c- p>(</c-><c- n>I</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>move</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>pair_reconstructible_range</c-></code>.
      <dd><sup>(2.2)</sup> Otherwise, <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>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>move</c-><c- p>(</c-><c- n>I</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>move</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>(2.3)</sup> <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>move</c-><c- p>(</c-><c- n>I</c-><c- p>),</c-> <c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>S</c-><c- p>))</c-></code> if it is a valid expression.
      <dd><sup>(2.4)</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>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> is ill-formed.
     </dl>
     <p></p>
     <p><sup>3</sup> Let <code class="highlight"><c- n>SR</c-></code> be some sub-expression. 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-></code> for some type <code class="highlight"><c- n>R</c-></code> and sub-expression <code class="highlight"><c- n>SR</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>move</c-><c- p>(</c-><c- n>SR</c-><c- p>))</c-></code> if it is a valid expression, and <code class="highlight"><c- n>R</c-></code> and <code class="highlight"><c- k>decltype</c-><c- p>(</c-><c- n>SR</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>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>ranges</c-><c- o>::</c-><c- n>begin</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>SR</c-><c- p>)),</c-> <c- n>ranges</c-><c- o>::</c-><c- n>end</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>move</c-><c- p>(</c-><c- n>SR</c-><c- p>)))</c-></code> if it is a valid expression and <code class="highlight"><c- n>R</c-></code>, <code class="highlight"><c- n>range</c-><c- o>::</c-><c- n>iterator_t</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>SR</c-><c- p>)</c-><c- o>></c-></code>, and <code class="highlight"><c- n>range</c-><c- o>::</c-><c- n>sentinel_t</c-><c- o>&lt;</c-><c- k>decltype</c-><c- p>(</c-><c- n>SR</c-><c- p>)</c-><c- o>></c-></code> model <code class="highlight"><c- n>pair_reconstructible_range</c-></code>.
      <dd><sup>(2.3)</sup> Otherwise, <code class="highlight"><c- k>return</c-> <c- n>SR</c-></code>.
     </dl>
     <p></p>
    </ins>
   </blockquote>
   <p>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>:</p>
   <blockquote>
    <ins>
<pre class="language-cpp highlight">	<c- c1>// [string.view.reconstruct]</c->
	<c- k>friend</c-> <c- k>constexpr</c-> <c- n>basic_string_view</c->
	<c- n>reconstruct</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>const_iterator</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
</pre>
    </ins>
   </blockquote>
   <p>Add a new subclause "§21.4.��� <code class="highlight"><c- n>Range</c-> <c- n>Reconstruction</c-></code>" [string.view.reconstruct] in §21.4:</p>
   <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>friend</c-> <c- k>constexpr</c-> <c- n>basic_string_view</c->
	<c- n>reconstruct</c-><c- p>(</c-><c- n>const_iterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>const_iterator</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
</pre>
     <p><sup>1</sup> Returns: <code class="highlight"><c- n>basic_string</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>
   <p>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>:</p>
   <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>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>
   <p>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:</p>
   <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>const_iterator</c-> <c- n>first</c-><c- p>,</c-> <c- n>const_iterator</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
</pre>
     <p><sup>1</sup> Constraints: Let <code class="highlight"><c- n>U</c-></code> be <code class="highlight"><c- n>remove_</c->­<c- n>reference_</c->­<c- n>t</c-><c- o>&lt;</c-><c- n>iter_</c->­<c- n>reference_</c->­<c- n>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_</c->­<c- n>convertible_</c->­<c- n>v</c-><c- o>&lt;</c-><c- n>U</c-><c- p>(</c-><c- o>*</c-><c- p>)[],</c-> <c- n>element_</c->­<c- n>type</c-><c- p>(</c-><c- o>*</c-><c- p>)[]</c-><c- o>></c-></code> is <code class="highlight">true</code>. [<i>Note 2</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> satisfies <code class="highlight"><c- n>contiguous_</c->­<c- n>iterator</c-></code>.
      <dd><sup>(1.3)</sup> — <code class="highlight"><c- n>End</c-></code> satisfies <code class="highlight"><c- n>sized_</c->­<c- n>sentinel_</c->­<c- k>for</c-><c- o>&lt;</c-><c- n>It</c-><c- o>></c-></code>.
      <dd><sup>(1.4)</sup> — <code class="highlight"><c- n>is_</c->­<c- n>convertible_</c->­<c- n>v</c-><c- o>&lt;</c-><c- n>End</c-><c- p>,</c-> <c- n>size_</c->­<c- n>t</c-><c- o>></c-></code> is <code class="highlight">false</code>.
     </dl>
     <p></p>
     <p><sup>2</sup> Let <code class="highlight"><c- n>MaybeExtent</c-></code> be an implementation-defined constant expression of type <code class="highlight"><c- b>size_t</c-></code>. If it is not equal to <code class="highlight"><c- n>dynamic_extent</c-></code>, then <code class="highlight"><c- n>MaybeExtent</c-></code> shall be a value equal to <code class="highlight"><c- n>distance</c-><c- p>(</c-><c- n>first</c-><c- p>,</c-> <c- n>last</c-><c- p>)</c-></code>.</p>
     <p><sup>3</sup> Returns: <code class="highlight"><c- n>span</c-><c- o>&lt;</c-><c- n>ElementType</c-><c- p>,</c-> <c- n>MaybeExtent</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> Remarks: the return type can 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>
   <p>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>:</p>
   <blockquote>
    <ins>
<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>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>
   <p>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:</p>
   <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>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->
</pre>
     <p><sup>1</sup> Returns: <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>
    </ins>
   </blockquote>
   <p>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>:</p>
   <blockquote>
    <ins>
<pre class="language-cpp highlight">	<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>sentinel</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
</pre>
    </ins>
   </blockquote>
   <p>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>]:</p>
   <blockquote>
    <ins>
<pre class="language-cpp highlight">	<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>sentinel</c-> <c- n>last</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
</pre>
     <p><sup>��</sup> Returns: <code class="highlight"><c- n>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-></code>.</p>
    </ins>
   </blockquote>
   <p>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>:</p>
   <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>iterator</c-><c- p>,</c-> <c- n>sentinel</c-><c- p>)</c-> <c- k>noexcept</c-> <c- p>{</c->
		<c- k>return</c-> <c- nf>empty_view</c-><c- p>();</c->
	<c- p>}</c->
</pre>
    </ins>
   </blockquote>
   <p>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:</p>
   <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_</c->­<c- n>cvref_</c->­<c- n>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_</c->­<c- n>difference_</c->­<c- n>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_</c->­<c- n>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_</c->­<c- n>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_</c->­<c- n>access_</c->­<c- n>range</c-></code> and <code class="highlight"><c- n>sized_</c->­<c- n>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_</c->­<c- n>extent</c-></code>,
        <dd><sup>(2.2.2)</sup> — a specialization of <code class="highlight"><c- n>basic_</c->­<c- n>string_</c->­<c- n>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_</c->­<c- n>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_</c->­<c- n>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_</c->­<c- n>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_</c->­<c- n>access_</c->­<c- n>range</c-></code>, <code class="highlight"><c- n>sized_</c->­<c- n>range</c-></code>, and <code class="highlight"><c- n>reconstructible_range</c-></code>, 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_</c->­<c- n>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>
   <p>Modify "§24.7.9.1 Overview " [<a href="http://eel.is/c++draft/range.drop.overview">range.take.overview</a>] for <code class="highlight"><c- n>views</c-><c- o>::</c-><c- n>drop</c-></code>'s paragraph 2:</p>
   <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_</c->­<c- n>cvref_</c->­<c- n>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_</c->­<c- n>difference_</c->­<c- n>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_</c->­<c- n>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_</c->­<c- n>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_</c->­<c- n>access_</c->­<c- n>range</c-></code> and <code class="highlight"><c- n>sized_</c->­<c- n>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_</c->­<c- n>extent</c-></code>,
        <dd><sup>(2.2.2)</sup> — a specialization of <code class="highlight"><c- n>basic_</c->­<c- n>string_</c->­<c- n>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_</c->­<c- n>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_</c->­<c- n>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_</c->­<c- n>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_</c->­<c- n>access_</c->­<c- n>range</c-></code>, <code class="highlight"><c- n>sized_</c->­<c- n>range</c-></code>, and <code class="highlight"><c- n>reconstructible_range</c-></code>, 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_</c->­<c- n>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>
   <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-n4835">[N4835]
   <dd>Richard Smith. <a href="https://wg21.link/n4835">Working Draft, Standard for Programming Language C++</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">mdspan: A Non-Owning Multidimensional Array Reference</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">Input Range Adaptors</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">A view of 0 or 1 elements: view::maybe</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">Range constructor for std::string_view</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">Range constructor for std::span</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">Transcoding the world - Standard Text Encoding</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">Avoid template bloat for safe_ranges in combination with 'subrange-y' view adaptors.</a>. 1 March 2020. URL: <a href="https://wg21.link/p1739r4">https://wg21.link/p1739r4</a>
   <dt id="biblio-range-v3">[RANGE-V3]
   <dd>Eric Niebler; Casey Carter. <a href="https://github.com/ericniebler/range-v3">range-v3</a>. June 11th, 2019. URL: <a href="https://github.com/ericniebler/range-v3">https://github.com/ericniebler/range-v3</a>
  </dl>