<!doctype html><html lang="en">
 <head>
  <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
  <meta content="width=device-width, initial-scale=1, shrink-to-fit=no" name="viewport">
  <title>P2645R0: path_view: a design that took a wrong turn</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;
	}

	.head a:hover > img[src*="logos/W3C"],
	.head a:focus > img[src*="logos/W3C"] {
		opacity: .8;
	}

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

	p {
		margin: 1em 0;
	}

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

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

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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

	/* Do something nice. */

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

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

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

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

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

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

	img {
		border-style: none;
	}

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

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

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

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

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

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

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


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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


/*
Alternate table alignment rules

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

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

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

Possible extra rowspan handling

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

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

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


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

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

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

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

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

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

		.toc li {
			clear: both;
		}

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

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

	@supports (display:grid) and (display:contents) {
		/* Use #toc over .toc to override non-@supports rules. */
		#toc {
			display: grid;
			align-content: start;
			grid-template-columns: auto 1fr;
			grid-column-gap: 1rem;
			column-gap: 1rem;
			grid-row-gap: .6rem;
			row-gap: .6rem;
		}
		#toc h2 {
			grid-column: 1 / -1;
			margin-bottom: 0;
		}
		#toc ol,
		#toc li,
		#toc a {
			display: contents;
			/* Switch <a> to subgrid when supported */
		}
		#toc span {
			margin: 0;
		}
		#toc > .toc > li > a > span {
			/* The spans of the top-level list,
			  comprising the first items of each top-level section. */
			margin-top: 1.1rem;
		}
		#toc#toc .secno { /* Ugh, need more specificity to override base.css */
			grid-column: 1;
			width: auto;
			margin-left: 0;
		}
		#toc .content {
			grid-column: 2;
			width: auto;
			margin-right: 1rem;
			border-bottom: 3px solid transparent;
			margin-bottom: -3px;
		}
		#toc .content:hover,
		#toc .content:focus {
			background: rgba(75%, 75%, 75%, .25);
			background: var(--a-hover-bg);
			border-bottom-color: #054572;
			border-bottom-color: var(--toclink-underline);
		}
		#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 a + span {
			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>
<style>
    table, th, td {
      border: 1px solid black;
      border-collapse: collapse;
      vertical-align: top;
    }
    th, td {
      border-left: none;
      border-right: none;
      padding: 0px 10px;
    }
    th {
      text-align: center;
    }

    del { background: #fcc; color: #000; text-decoration: line-through; }
    ins { background: #cfc; color: #000; }
    blockquote .highlight:not(.idl) { background: initial; margin: initial; padding: 0.5em }
    blockquote ul { background: inherit; }
    blockquote code.highlight:not(.idl) { padding: initial; }
    blockquote c-[a] { color: inherit; } /* Keyword.Declaration */
    blockquote c-[b] { color: inherit; } /* Keyword.Type */
    blockquote c-[c] { color: inherit; } /* Comment */
    blockquote c-[d] { color: inherit; } /* Comment.Multiline */
    blockquote c-[e] { color: inherit; } /* Name.Attribute */
    blockquote c-[f] { color: inherit; } /* Name.Tag */
    blockquote c-[g] { color: inherit; } /* Name.Variable */
    blockquote c-[k] { color: inherit; } /* Keyword */
    blockquote c-[l] { color: inherit; } /* Literal */
    blockquote c-[m] { color: inherit; } /* Literal.Number */
    blockquote c-[n] { color: inherit; } /* Name */
    blockquote c-[o] { color: inherit; } /* Operator */
    blockquote c-[p] { color: inherit; } /* Punctuation */
    blockquote c-[s] { color: inherit; } /* Literal.String */
    blockquote c-[t] { color: inherit; } /* Literal.String.Single */
    blockquote c-[u] { color: inherit; } /* Literal.String.Double */
    blockquote c-[cp] { color: inherit; } /* Comment.Preproc */
    blockquote c-[c1] { color: inherit; } /* Comment.Single */
    blockquote c-[cs] { color: inherit; } /* Comment.Special */
    blockquote c-[kc] { color: inherit; } /* Keyword.Constant */
    blockquote c-[kn] { color: inherit; } /* Keyword.Namespace */
    blockquote c-[kp] { color: inherit; } /* Keyword.Pseudo */
    blockquote c-[kr] { color: inherit; } /* Keyword.Reserved */
    blockquote c-[ld] { color: inherit; } /* Literal.Date */
    blockquote c-[nc] { color: inherit; } /* Name.Class */
    blockquote c-[no] { color: inherit; } /* Name.Constant */
    blockquote c-[nd] { color: inherit; } /* Name.Decorator */
    blockquote c-[ni] { color: inherit; } /* Name.Entity */
    blockquote c-[ne] { color: inherit; } /* Name.Exception */
    blockquote c-[nf] { color: inherit; } /* Name.Function */
    blockquote c-[nl] { color: inherit; } /* Name.Label */
    blockquote c-[nn] { color: inherit; } /* Name.Namespace */
    blockquote c-[py] { color: inherit; } /* Name.Property */
    blockquote c-[ow] { color: inherit; } /* Operator.Word */
    blockquote c-[mb] { color: inherit; } /* Literal.Number.Bin */
    blockquote c-[mf] { color: inherit; } /* Literal.Number.Float */
    blockquote c-[mh] { color: inherit; } /* Literal.Number.Hex */
    blockquote c-[mi] { color: inherit; } /* Literal.Number.Integer */
    blockquote c-[mo] { color: inherit; } /* Literal.Number.Oct */
    blockquote c-[sb] { color: inherit; } /* Literal.String.Backtick */
    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 */
    blockquote c-[il] { color: inherit; } /* Literal.Number.Integer.Long */
  </style>
  <meta content="Bikeshed version 4416b18d5, updated Tue Jan 2 15:52:39 2024 -0800" name="generator">
  <link href="https://isocpp.org/favicon.ico" rel="icon">
  <meta content="a05840ce3a8aa1e4efab03ccb71e887a3224ef78" name="revision">
<style>/* Boilerplate: style-autolinks */
.css.css, .property.property, .descriptor.descriptor {
    color: var(--a-normal-text);
    font-size: inherit;
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   <p data-fill-with="logo"></p>
   <h1 class="p-name no-ref" id="title">P2645R0<br><code class="highlight"><c- n>path_view</c-></code>: a design that took a wrong turn</h1>
   <h2 class="no-num no-toc no-ref heading settled" id="profile-and-date"><span class="content">Published Proposal, <time class="dt-updated" datetime="2024-09-10">2024-09-10</time></span></h2>
   <div data-fill-with="spec-metadata">
    <dl>
     <dt class="editor">Author:
     <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:victor.zverovich@gmail.com">Victor Zverovich</a>
     <dt>Audience:
     <dd>LEWG
     <dt>Project:
     <dd>ISO/IEC 14882 Programming Languages — C++, ISO/IEC JTC1/SC22/WG21
    </dl>
   </div>
   <div data-fill-with="warning"></div>
   <hr title="Separator for header">
  </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="#intro"><span class="secno">1</span> <span class="content">Introduction</span></a>
    <li>
     <a href="#problems"><span class="secno">2</span> <span class="content">Problems</span></a>
     <ol class="toc">
      <li><a href="#encoding"><span class="secno">2.1</span> <span class="content">Encoding</span></a>
      <li><a href="#impl"><span class="secno">2.2</span> <span class="content">Implementation and usage experience</span></a>
      <li><a href="#perf"><span class="secno">2.3</span> <span class="content">Performance</span></a>
      <li><a href="#format"><span class="secno">2.4</span> <span class="content">Formatting and output</span></a>
      <li><a href="#complexity"><span class="secno">2.5</span> <span class="content">Complexity</span></a>
      <li><a href="#conclusion"><span class="secno">2.6</span> <span class="content">Conclusion</span></a>
     </ol>
    <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>
   <p style="text-align: right"> "Your scientists were so preoccupied with whether or not they could, they
didn’t stop to think if they should." <br> — Dr. Ian Malcolm </p>
   <h2 class="heading settled" data-level="1" id="intro"><span class="secno">1. </span><span class="content">Introduction</span><a class="self-link" href="#intro"></a></h2>
   <p>P1030 <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path_view</c-></code> is a paper with a long and troubled history,
consistently falling short of its original goals and, in some cases, even
regressing. While recent revisions have removed some of the more questionable
parts of the design, such as the use of locales, numerous critical issues remain
unresolved. This paper highlights some of these issues and argues that
standardizing <code class="highlight"><c- n>path_view</c-></code> in its current form would not only perpetuate past
design flaws but also make future fixes nearly impossible. Additionally, it
points out the severe lack of implementation and practical usage experience with
the latest design.</p>
   <h2 class="heading settled" data-level="2" id="problems"><span class="secno">2. </span><span class="content">Problems</span><a class="self-link" href="#problems"></a></h2>
   <h3 class="heading settled" data-level="2.1" id="encoding"><span class="secno">2.1. </span><span class="content">Encoding</span><a class="self-link" href="#encoding"></a></h3>
   <p>A significant portion of the initial revision of the paper (<a data-link-type="biblio" href="#biblio-p1030r0" title="P1030R0: `std::filesystem::path_view`">[P1030R0]</a>) was
devoted to examining the issues surrounding <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code> and the use
of ANSI encodings on Windows:</p>
   <blockquote>
    <p><code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-></code> came originally from Boost.Filesystem, which in turn
underwent three major revisions during the Boost peer review as it was such a
lively debate. During those reviews, it was considered very important that
paths were passed through, unmodified, to the system API. There are very good
reasons for this, mainly that filesystems, for the most part, treat filenames
as a bunch of bytes without interpreting them as anything. So any character
reencoding could cause a path entered via copy-and-paste from the user to be
unopenable, unless the bytes were passed through exactly.</p>
    <p>This is a laudable aim, and it is preserved in this path view proposal.
Unfortunately it has a most unfortunate side effect: on Microsoft Windows, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code> when supplied with <code class="highlight"><c- b>char</c-></code> not <code class="highlight"><c- b>wchar_t</c-></code>, is considered
to be in <em>ANSI</em> encoding. This is because the <code class="highlight"><c- b>char</c-></code> accepting syscalls on
Microsoft Windows consume ANSI for compatibility with Windows 3.1, and they
simply thunk through to the UTF-16 accepting syscall after allocating a buffer
and copying the input bytes into shorts. Therefore on Microsoft Windows, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code> duly expands <code class="highlight"><c- b>char</c-></code> input into its internal UTF-16 <code class="highlight"><c- b>wchar_t</c-></code> storage via direct casting. It does not perform a UTF-8 to UTF-16
conversion.</p>
    <p>Unfortunately any Microsoft Windows IDE or text editor that I have used
recently defaults to creating C++ source files in UTF-8, exactly the same as
on every other major platform including Linux and MacOS. This in turn means
that source code with a char string literal such as <code class="highlight"><c- s>"UTF♠stringΩliteral"</c-></code> makes a UTF-8 char string, not an ANSI char string, which is consistent
across all the major platforms. Thus, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code>’s behaviour on
Microsoft Windows is quite surprising: your portable program will not work.
What works on all the other platforms, without issue, does not work on
Microsoft Windows, for no obvious reason to the uninitiated.</p>
    <p>This author can only speak from his own personal experience, but what he has
found over many years of practice in writing portable code based on <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code> is that one ends up inevitably using preprocessor
macros to emit <code class="highlight">L<c- s>"UTF♠stringΩliteral"</c-></code> when <code class="highlight"><c- n>_WIN32</c-></code> and <code class="highlight"><c- n>_UNICODE</c-></code> are macro
defined, and otherwise emit <code class="highlight"><c- s>"UTF♠stringΩliteral"</c-></code>. The reason is simple: the
same string literal, with merely a <code class="highlight"><c- n>L</c-></code> or not prefix, works identically on all
platforms, no locale induced surprises, because we know that string literals
in UTF source code will be in some UTF-x format. The side effect is spamming
your ‘portable’ program code with string literal wrapper macros as if we were
still writing for MFC, and/or <code class="highlight"><c- cp>#if defined(_WIN32) &amp;&amp; defined(_UNICODE)</c-></code> all
over your code. I do not find this welcome.</p>
   </blockquote>
   <p>R0 goes as far as to switch to UTF-8 as the default encoding for <code class="highlight"><c- n>path_view</c-></code>:</p>
   <blockquote>
    <p>I propose that when char strings are supplied as a path string literal, and
if and only if a conversion is needed, that we interpret those chars as UTF-8.</p>
    <p>I know that this is a breaking change from <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code>, but I
would argue that <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code> needs to be similarly changed. UTF-8
source code is very, very commonplace now, much more so than even a few years
ago, and it is extremely likely that almost all new C++ written will be in
UTF-8. So best to change <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code> appropriately, and if that
is too great a breaking change, then these proposed path views are ‘fixed’
instead.</p>
   </blockquote>
   <p>While this revision confuses source and literal encoding and presents an overly
ambitious solution, the problems described by the author are very real. In fact,
they have worsened as UTF-8 adoption has increased on Windows, particularly with
the ease of enabling UTF-8 via the <code class="highlight"><c- o>/</c-><c- n>utf</c-><c- mi>-8</c-></code> compiler flag in MSVC.</p>
   <p>Working with certain parts of <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code> is very error-prone for
the increasingly common case of literal encoding being UTF-8. Unfortunately,
later revisions of P1030 not only dropped any attempt to address this problem
but exacerbated it by adopting the legacy ANSI encoding throughout the API.
Worse still, this encoding has been embedded in the internal representation,
making it part of the ABI — a major regression compared to <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code>, where the use of ANSI encoding is far more limited and
rightfully avoided in the internal representation.</p>
   <p><a data-link-type="biblio" href="#biblio-p2319" title="Prevent path presentation problems">[P2319]</a>, which was recently approved by SG16 with strong support, proposes
to deprecate the most problematic (from the encoding standpoint) parts of <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code>. <a data-link-type="biblio" href="#biblio-p1030r6" title="P1030R6: `std::filesystem::path_view`">[P1030R6]</a> does the opposite and massively increases
the public API (and ABI) surface that relies on error-prone legacy codepages.</p>
   <p>In addition to problems described in P1030R0, the use of ANSI encoding makes
it hard for <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path_view</c-></code> to interoperate with modern facilities
such as C++20 <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>format</c-></code> and C++23 <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>print</c-></code> (see <a href="#format">Formatting</a>).</p>
   <h3 class="heading settled" data-level="2.2" id="impl"><span class="secno">2.2. </span><span class="content">Implementation and usage experience</span><a class="self-link" href="#impl"></a></h3>
   <p><a data-link-type="biblio" href="#biblio-p1030r6" title="P1030R6: `std::filesystem::path_view`">[P1030R6]</a> claims:</p>
   <blockquote>
    <p>If you wish to use an implementation right now, a highly-conforming reference
implementation of the proposed path view can be found at <a href="https://github.com/ned14/llfio/blob/master/include/llfio/v2.0/path_view.hpp">https://github.com/ned14/llfio/blob/master/include/llfio/v2.0/path_view.hpp</a>.</p>
   </blockquote>
   <p>Unfortunately, at the time of writing, important parts of the proposal are
missing from that implementation. Specifically, more than 80 new overloads (for
functions like <code class="highlight"><c- n>absolute</c-></code> to <code class="highlight"><c- n>weakly_canonical</c-></code>) remain unimplemented. Even
worse, the paper itself lacks wording for these functions:</p>
   <blockquote>
    <p><em>Wording note</em>: The definitions for the function declared in the synopsis
above are not provided at this time. All of them delegate to the overload
taking a <code class="highlight"><c- n>path</c-></code>.</p>
   </blockquote>
   <p>Additionally, there is no implementation of a <em>path-view-like</em> equivalent that
was designed on-the-fly during one of the LEWG reviews. As a result, there is no
way to evaluate the effects of switching to <code class="highlight"><c- n>path_view</c-></code> in these functions on
real-world user code.</p>
   <p>At the time of writing, there are zero uses of <code class="highlight"><c- n>render_zero_terminated</c-></code> (referred to as <code class="highlight"><c- n>render_null_terminated</c-></code> in the paper) on GitHub, aside from its
definition and a mention in a blog. Furthermore, there are no tests available,
despite it being one of the primary APIs.</p>
   <h3 class="heading settled" data-level="2.3" id="perf"><span class="secno">2.3. </span><span class="content">Performance</span><a class="self-link" href="#perf"></a></h3>
   <p><code class="highlight"><c- n>path_view</c-></code> in its current form exacerbates encoding problems, but does it at
least offer performance improvements?</p>
   <p>Unfortunately, <code class="highlight"><c- n>path_view</c-></code> goes to great lengths to avoid providing any
performance benefits for existing users. This is achieved through obscure <em>path-view-like</em> overloads so that</p>
   <blockquote>
    <p>existing C++ code would need to ‘opt in’ to using the path view overloads</p>
   </blockquote>
   <p>This stands in stark contrast to the common use of <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string_view</c-></code>, which
typically allows users to avoid <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string</c-></code> allocations:</p>
<pre class="language-c++ highlight"><c- b>void</c-> <c- nf>f</c-><c- p>(</c-><c- n>std</c-><c- o>::</c-><c- n>string_view</c-> <c- n>s</c-><c- p>);</c->

<c- n>f</c-><c- p>(</c-><c- s>"foo"</c-><c- p>);</c-> <c- c1>// No allocation</c->

<c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>file_size</c-><c- p>(</c-><c- s>"/path/to/file"</c-><c- p>);</c-> <c- c1>// Allocates std::filesystem::path</c->
                                             <c- c1>// in P1030R6.</c->
</pre>
   <p>Additionally, due to lazy transcoding, <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path_view</c-></code> can be
slower than <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code>, which transcodes eagerly, when used
multiple times.</p>
   <h3 class="heading settled" data-level="2.4" id="format"><span class="secno">2.4. </span><span class="content">Formatting and output</span><a class="self-link" href="#format"></a></h3>
   <p>Unlike <code class="highlight"><c- n>path</c-></code>, <code class="highlight"><c- n>path_view</c-></code> proposed by <a data-link-type="biblio" href="#biblio-p1030r6" title="P1030R6: `std::filesystem::path_view`">[P1030R6]</a> does not provide a formatter
so the following examples do not compile:</p>
<pre class="language-c++ highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path_view</c-> <c- n>pv</c-> <c- o>=</c-> <c- p>...;</c->
<c- n>std</c-><c- o>::</c-><c- n>string</c-> <c- n>s</c-> <c- o>=</c-> <c- n>std</c-><c- o>::</c-><c- n>format</c-><c- p>(</c-><c- s>"/tmp/"</c-><c- p>)</c-> <c- o>+</c-> <c- n>pv</c-><c- p>;</c->
<c- n>std</c-><c- o>::</c-><c- n>print</c-><c- p>(</c-><c- s>"{}"</c-><c- p>,</c-> <c- n>pv</c-><c- p>);</c->
</pre>
   <p>Implementing this functionality may be problematic due to unfortunate choices
in the latest design.</p>
   <p>One issue is related to encoding. The representation of <code class="highlight"><c- n>path</c-></code> uses a single
encoding that remains constant at runtime, making it feasible — though not
trivial — to specify a good formatter. In contrast, <code class="highlight"><c- n>path_view</c-></code> complicates
matters by using multiple representations with different encodings, one of which
can be a legacy encoding that can change at runtime. As a result, there is no
way to determine which encoding <code class="highlight"><c- n>path_view</c-></code> was constructed with at the time of
use. This is conceptually similar to the Time of Check to Time of Use
(<a data-link-type="biblio" href="#biblio-toctou" title="Time-of-check to time-of-use">[TOCTOU]</a>) class of problems common in filesystem operations, which in this
case can lead to mojibake, data corruption and other problems.</p>
   <p>Another issue is the binary representation, which is severely underspecified and
may conflict with other representations, making output hard to round-trip, even
within a single implementation. Writing as an author of the path formatter
(<a data-link-type="biblio" href="#biblio-p2845" title="Formatting of std::filesystem::path">[P2845]</a>), it remains unclear how it should be defined, and despite multiple
requests, <a data-link-type="biblio" href="#biblio-p1030r6" title="P1030R6: `std::filesystem::path_view`">[P1030R6]</a> still has failed to provide the necessary specifics.</p>
   <p><code class="highlight"><c- k>operator</c-><c- o>&lt;&lt;</c-></code> is defined in terms of <em>path-from-binary</em> which is very vague and
appears to have the same problems.</p>
   <h3 class="heading settled" data-level="2.5" id="complexity"><span class="secno">2.5. </span><span class="content">Complexity</span><a class="self-link" href="#complexity"></a></h3>
   <p><code class="highlight"><c- n>path_view</c-></code> roughly doubles the API surface area of <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code>,
both in terms of its own definition and by proposing to add an overload that
takes <em>path-view-like</em> arguments for every existing overload that takes <code class="highlight"><c- n>path</c-></code>.
For example:</p>
<pre class="highlight"><c- b>bool</c-> <c- nf>equivalent</c-><c- p>(</c-><c- k>const</c-> <c- n>path</c-><c- o>&amp;</c-> <c- n>p1</c-><c- p>,</c-> <c- k>const</c-> <c- n>path</c-><c- o>&amp;</c-> <c- n>p2</c-><c- p>);</c->
<c- b>bool</c-> <c- nf>equivalent</c-><c- p>(</c-><c- k>const</c-> <c- n>path</c-><c- o>&amp;</c-> <c- n>p1</c-><c- p>,</c-> <c- k>const</c-> <c- n>path</c-><c- o>&amp;</c-> <c- n>p2</c-><c- p>,</c-> <c- n>error_code</c-><c- o>&amp;</c-> <c- n>ec</c-><c- p>)</c-> <c- k>noexcept</c-><c- p>;</c->
</pre>
<pre class="highlight"><ins><c- b>bool</c-> <c- nf>equivalent</c-><c- p>(</c-><c- n>path</c-><c- o>-</c-><c- n>view</c-><c- o>-</c-><c- n>like</c-> <c- n>p1</c-><c- p>,</c-> <c- n>path</c-><c- o>-</c-><c- n>view</c-><c- o>-</c-><c- n>like</c-> <c- n>p2</c-><c- p>);</c->
<c- b>bool</c-> <c- nf>equivalent</c-><c- p>(</c-><c- n>path</c-><c- o>-</c-><c- n>view</c-><c- o>-</c-><c- n>like</c-> <c- n>p1</c-><c- p>,</c-> <c- n>path</c-><c- o>-</c-><c- n>view</c-><c- o>-</c-><c- n>like</c-> <c- n>p2</c-><c- p>,</c-> <c- n>error_code</c-><c- o>&amp;</c-> <c- n>ec</c-><c- p>)</c-><c- k>noexcept</c-><c- p>;</c-></ins>
</pre>
   <p>Contrary to its name, the proposed <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path_view</c-></code> is not truly a
view of <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path</c-></code> in the same way that <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string_view</c-></code> can be
considered a view of <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>string</c-></code>. <code class="highlight"><c- n>path</c-></code> has a single representation that is
suitable for the current system. In contrast, <code class="highlight"><c- n>path_view</c-></code> is effectively a
discriminated union of some (but not all) of the types from which <code class="highlight"><c- n>path</c-></code> can be
constructed, with a lazy conversion to path. It is unclear what such an unusual
API should be called, but it probably should not be referred to as a "view."</p>
   <h3 class="heading settled" data-level="2.6" id="conclusion"><span class="secno">2.6. </span><span class="content">Conclusion</span><a class="self-link" href="#conclusion"></a></h3>
   <p>In summary, the proposed <code class="highlight"><c- n>std</c-><c- o>::</c-><c- n>filesystem</c-><c- o>::</c-><c- n>path_view</c-></code> presents significant
concerns that need to be resolved before standardization. Its design exacerbates
encoding problems and adds unnecessary complexity to the API. The reliance on 
legacy ANSI encoding undermines modern practices and complicates
interoperability with other C++ facilities.</p>
   <p>Additionally, the increased API surface area and the requirement for users to
opt in to specific overloads detract from its usability. To maximize the utility
of <code class="highlight"><c- n>path_view</c-></code>, future revisions should focus on simplifying its design,
addressing encoding issues, enhancing compatibility with existing libraries and
getting actual implementation and usage experience. Standardizing the current
proposal risks introducing more problems than it solves.</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-p1030r0">[P1030R0]
   <dd>Niall Douglas. <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1030r0.pdf"><cite>P1030R0: `std::filesystem::path_view`</cite></a>. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1030r0.pdf">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2018/p1030r0.pdf</a>
   <dt id="biblio-p1030r6">[P1030R6]
   <dd>Niall Douglas. <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p1030r6.pdf"><cite>P1030R6: `std::filesystem::path_view`</cite></a>. URL: <a href="https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p1030r6.pdf">https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2023/p1030r6.pdf</a>
   <dt id="biblio-p2319">[P2319]
   <dd>Victor Zverovich. <a href="https://wg21.link/p2319"><cite>Prevent path presentation problems</cite></a>. URL: <a href="https://wg21.link/p2319">https://wg21.link/p2319</a>
   <dt id="biblio-p2845">[P2845]
   <dd>Victor Zverovich. <a href="https://wg21.link/p2845"><cite>Formatting of std::filesystem::path</cite></a>. URL: <a href="https://wg21.link/p2845">https://wg21.link/p2845</a>
   <dt id="biblio-toctou">[TOCTOU]
   <dd><a href="https://en.wikipedia.org/wiki/Time-of-check_to_time-of-use"><cite>Time-of-check to time-of-use</cite></a>. URL: <a href="https://en.wikipedia.org/wiki/Time-of-check_to_time-of-use">https://en.wikipedia.org/wiki/Time-of-check_to_time-of-use</a>
  </dl>