<!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,
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  <title>P1161R1: Deprecate uses of the comma operator in subscripting expressions</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
 *
 * 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)
 *   - .assertion  for assertions                    (div, p, span)
 *   - .advisement for loud normative statements     (div, p, strong)
 *   - .annoying-warning for spec obsoletion notices (div, aside, details)
 *
 * 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
 *
 * 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)
 *
 ******************************************************************************/

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

	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;

		/* Colors */
		color: black;
		background: white 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-width: .65rem .7rem .6rem;
		border-radius: .4rem;
		background: #1a5e9a;
		color: white;
		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;
		border-color: #c00;
	}

	/* 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: 2;
			bottom: 0; left: 0;
			margin: 0;
			min-width: 1.33em;
			border-top-right-radius: 2rem;
			box-shadow: 0 0 2px;
			font-size: 1.5em;
			color: black;
		}
		#toc-nav > a {
			display: block;
			white-space: nowrap;

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

			background: white;
			box-shadow: 0 0 2px;
			border: none;
			border-top-right-radius: 1.33em;
			background: white;
		}
		#toc-nav > #toc-jump {
			padding-bottom: 2em;
			margin-bottom: -1.9em;
		}

		#toc-nav > a:hover,
		#toc-nav > a:focus {
			background: #f8f8f8;
		}
		#toc-nav > a:not(:hover):not(:focus) {
			color: #707070;
		}

		/* 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-toggle-inline {
			vertical-align: 0.05em;
			font-size: 80%;
			color: gray;
			color: hsla(203,20%,40%,.7);
			border-style: none;
			background: transparent;
			position: relative;
		}
		#toc-toggle-inline:hover:not(:active),
		#toc-toggle-inline:focus:not(:active) {
			text-shadow: 1px 1px silver;
			top: -1px;
			left: -1px;
		}

		#toc-nav :active {
			color: #C00;
		}
	}

/** 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);
			background: inherit;
			background-color: #f7f8f9;
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) 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);
		}
		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);
			background: inherit;
			background-color: #f7f8f9;
			z-index: 1;
			box-shadow: -.1em 0 .25em rgba(0,0,0,.1) 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);
		}

		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;
		background: transparent;
	}

	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) > hr {
		font-size: 1.5em;
		text-align: center;
		margin: 1em auto;
		height: auto;
		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;
	}

	/* Put nice boxes around each algorithm. */
	[data-algorithm]:not(.heading) {
	  padding: .5em;
	  border: thin solid #ddd; 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: medium;
	}
	dfn var {
		font-style: normal;
	}

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

	del { color: red;  text-decoration: line-through; }
	ins { color: #080; text-decoration: underline;    }

/** 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;
		page-break-inside: avoid;
		hyphens: none;
		text-transform: none;
	}
	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;
		text-decoration: none;
		border-bottom: 1px solid #707070;
		/* Need a bit of extending for it to look okay */
		padding: 0 1px 0;
		margin: 0 -1px 0;
	}
	a:visited {
		border-bottom-color: #BBB;
	}

	/* Use distinguishing colors when user is interacting with the link */
	a[href]:focus,
	a[href]:hover {
		background: #f8f8f8;
		background: rgba(75%, 75%, 75%, .25);
		border-bottom-width: 3px;
		margin-bottom: -2px;
	}
	a[href]:active {
		color: #C00;
		border-color: #C00;
	}

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

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

	img {
		border-style: none;
	}

	/* 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;
	}
	.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 {
		padding: .5em;
		border: .5em;
		border-left-style: solid;
		page-break-inside: avoid;
	}
	span.issue, span.note {
		padding: .1em .5em .15em;
		border-right-style: solid;
	}

	.issue,
	.note,
	.example,
	.advisement,
	.assertion,
	blockquote {
		margin: 1em auto;
	}
	.note  > p:first-child,
	.issue > p:first-child,
	blockquote > :first-child {
		margin-top: 0;
	}
	blockquote > :last-child {
		margin-bottom: 0;
	}

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

	blockquote {
		border-color: silver;
	}

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

	.issue {
		border-color: #E05252;
		background: #FBE9E9;
		counter-increment: issue;
		overflow: auto;
	}
	.issue::before, .issue > .marker {
		text-transform: uppercase;
		color: #AE1E1E;
		padding-right: 1em;
		text-transform: uppercase;
	}
	/* 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;
		background: #FCFAEE;
		counter-increment: example;
		overflow: auto;
		clear: both;
	}
	.example::before, .example > .marker {
		text-transform: uppercase;
		color: #827017;
		min-width: 7.5em;
		display: block;
	}
	/* 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;
		background: #E9FBE9;
		overflow: auto;
	}

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

	details.note > summary {
		display: block;
		color: hsl(120, 70%, 30%);
	}
	details.note[open] > summary {
		border-bottom: 1px silver solid;
	}

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

	.assertion {
		border-color: #AAA;
		background: #EEE;
	}

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

	.advisement {
		border-color: orange;
		border-style: none solid;
		background: #FFEECC;
	}
	strong.advisement {
		display: block;
		text-align: center;
	}
	.advisement > .marker {
		color: #B35F00;
	}

/** 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: #fdd;
		color: red;
		font-weight: bold;
		padding: .75em 1em;
		border: thick red;
		border-style: solid;
		border-radius: 1em;
	}
	.annoying-warning :last-child {
		margin-bottom: 0;
	}

@media not print {
	details.annoying-warning[open] {
		position: fixed;
		left: 1em;
		right: 1em;
		bottom: 1em;
		z-index: 1000;
	}
}

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

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

	.def {
		padding: .5em 1em;
		background: #DEF;
		margin: 1.2em 0;
		border-left: 0.5em solid #8CCBF2;
	}

/******************************************************************************/
/*                                    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;
	}

	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-top-style: solid;
	}

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

	table.data  thead,
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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">P1161R1<br>Deprecate uses of the comma operator in subscripting expressions</h1>
   <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">Published Proposal, <time class="dt-updated" datetime="2018-10-07">2018-10-07</time></span></h2>
   <div data-fill-with="spec-metadata">
    <dl>
     <dt>This version:
     <dd><a class="u-url" href="https://cor3ntin.github.io/CPPProposals/deprecate_comma_subscript/P0000.html">https://cor3ntin.github.io/CPPProposals/deprecate_comma_subscript/P0000.html</a>
     <dt>Author:
     <dd>
      <dd class="editor p-author h-card vcard"><a class="p-name fn u-email email" href="mailto:corentin.jabot@gmail.com">Corentin Jabot</a>
     <dt>Audience:
     <dd>EWG
     <dt>Project:
     <dd>ISO/IEC JTC1/SC22/WG21 14882: Programming Language — C++
    </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>We propose to deprecate the use of the comma operator in subscripting expressions as they are not very useful, confusing and limit futures evolutions of the standard.</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="#intro"><span class="secno">1</span> <span class="content">Introduction</span></a>
    <li>
     <a href="#motivation"><span class="secno">2</span> <span class="content">Motivation</span></a>
     <ol class="toc">
      <li><a href="#the-need-for-a-multidimensional-subscript-operator"><span class="secno">2.1</span> <span class="content">The need for a multidimensional subscript operator</span></a>
      <li><a href="#what-a-multidimensional-subscript-operator-would-look-like"><span class="secno">2.2</span> <span class="content">What a multidimensional subscript operator would look like</span></a>
     </ol>
    <li><a href="#impact-on-existing-code-bases"><span class="secno">3</span> <span class="content">Impact on existing code bases</span></a>
    <li>
     <a href="#alternative-approaches"><span class="secno">4</span> <span class="content">Alternative approaches</span></a>
     <ol class="toc">
      <li><a href="#allow-comma-expression-only-in-c-arrays"><span class="secno">4.1</span> <span class="content">Allow comma expression only in C arrays</span></a>
      <li><a href="#alternative-syntax-for-multidimensional-subscript-expressions"><span class="secno">4.2</span> <span class="content">Alternative syntax for multidimensional subscript expressions</span></a>
      <li>
       <a href="#other-comma-expressions"><span class="secno">4.3</span> <span class="content">Other comma expressions</span></a>
       <ol class="toc">
        <li><a href="#without-duplication-caused-by-headers-included-multiple-times-throughout-a-project"><span class="secno">4.3.1</span> <span class="content">Without duplication caused by headers included multiple times throughout a project</span></a>
        <li><a href="#non-deduplicated-results"><span class="secno">4.3.2</span> <span class="content">Non-Deduplicated results.</span></a>
       </ol>
     </ol>
    <li>
     <a href="#proposed-wording"><span class="secno">5</span> <span class="content">Proposed Wording</span></a>
     <ol class="toc">
      <li><a href="#d-comma-operator-in-subscript-expressions"><span class="secno">5.1</span> <span class="content">D.� Comma operator in subscript expressions</span></a>
     </ol>
    <li><a href="#acknowledgments"><span class="secno">6</span> <span class="content">Acknowledgments</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="intro"><span class="secno">1. </span><span class="content">Introduction</span><a class="self-link" href="#intro"></a></h2>
   <p>This paper proposes that the use of a comma operator within a subscripting expression be deprecated.
Doing so opens the door to multidimensional subscript operators for classes such as <code class="highlight"><c- n>mdspan</c-></code>.</p>
   <table class="tony-table">
    <tbody>
     <tr>
      <th> Current 
      <th> Proposed 
     <tr>
      <td>
<pre class="highlight"><c- n>array</c-><c- p>[</c-><c- n>x</c-><c- p>]</c->     <c- c1>// Ok</c->
<c- n>array</c-><c- p>[(</c-><c- n>x</c-><c- p>,</c-><c- n>y</c-><c- p>)]</c-> <c- c1>// Ok, uses y as index/key</c->
<c- n>array</c-><c- p>[</c-><c- n>x</c-><c- p>,</c-><c- n>y</c-><c- p>]</c->   <c- c1>// Ok, uses y as index/key</c->
</pre>
      <td>
<pre class="highlight"><c- n>array</c-><c- p>[</c-><c- n>x</c-><c- p>]</c->      <c- c1>// Ok</c->
<c- n>array</c-><c- p>[(</c-><c- n>x</c-><c- p>,</c-><c- n>y</c-><c- p>)]</c->  <c- c1>// Ok, uses y as index/key</c->
<c- n>array</c-><c- p>[</c-><c- n>x</c-><c- p>,</c-><c- n>y</c-><c- p>]</c->   <c- c1> // </c-><b><c- c1>Deprecated</c-></b><c- c1>, uses y as index/key</c->
</pre>
   </table>
   <h2 class="heading settled" data-level="2" id="motivation"><span class="secno">2. </span><span class="content">Motivation</span><a class="self-link" href="#motivation"></a></h2>
   <p>Currently, a comma can appear in subscript expressions such that <code class="highlight"><c- k>auto</c-> <c- n>z</c-> <c- o>=</c-> <c- n>foo</c-><c- p>[</c-><c- n>x</c-><c- p>,</c-> <c- n>y</c-><c- p>]</c-></code> calls the comma operator with <code class="highlight"><c- n>y</c-></code> as the argument.
While this is currently unambiguous, it is confusing when encountered and error-prone when used.</p>
   <p>The authors think this syntax would be more useful and suited to index multidimensional classes such as <code class="highlight"><c- n>mdspan</c-></code>.</p>
<pre class="highlight"><c- n>mdspan</c-><c- o>&lt;</c-><c- b>int</c-><c- p>,</c-> <c- n>array_property</c-><c- o>::</c-><c- n>dimension</c-><c- o>&lt;</c-><c- mi>2</c-><c- p>,</c-> <c- mi>3</c-><c- p>,</c-> <c- mi>5</c-><c- o>>></c-> <c- n>foo</c-><c- p>(</c-><c- d>/*...*/</c-><c- p>);</c->
<c- b>int</c-> <c- n>value</c-> <c- o>=</c-> <c- n>foo</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->
</pre>
   <p>We do not propose to make this possible until a reasonable deprecation period has passed.</p>
   <p>However <a data-link-type="biblio" href="#biblio-p1277">[P1277]</a> suggests a shortest depreciation period and provides wording for a multi-dimensional operator subscript.</p>
   <p>It is the hope of the authors that <code class="highlight"><c- n>mdspan</c-></code> will be able to adopt such an operator in a timely fashionn
rather than nastily re-purposing the call operator for lack or a more suitable alternative.</p>
   <p>It is important to note that the goal is not to special-casing the meaning of a comma within a subscript expression.
Indeed, the standard defines that:</p>
   <blockquote>
    <p>In contexts where comma is given a special meaning, <em>[ Example: in lists of arguments to functions ([expr.call]) and lists of initializers ([dcl.init]) — end example ]</em> the comma operator as described in this subclause can appear only in parentheses.</p>
   </blockquote>
   <p>So simply by supporting multiple parameters, a comma within a subscript operator
would serve as an argument separator, without the need for specific wording or parsing.</p>
   <h3 class="heading settled" data-level="2.1" id="the-need-for-a-multidimensional-subscript-operator"><span class="secno">2.1. </span><span class="content">The need for a multidimensional subscript operator</span><a class="self-link" href="#the-need-for-a-multidimensional-subscript-operator"></a></h3>
   <p>The classes that can benefit from a multidimensional subscript operator are higher-dimensions variants of
classes that define a single-dimension subscript operator: matrixes, views, geometric entities, graphics APIs...</p>
   <p><code class="highlight"><c- n>mdspan</c-></code> comes immediately to mind. Note that because there is no multidimensional subscript operator in the standard, <code class="highlight"><c- n>mdspan</c-></code> uses the call operator. While this is functionally equivalent to what a multidimensional subscript operator would
be, it does not carry the same semantic, making the code harder to read and reason about.
It also encourages non-semantical operator overloading.</p>
   <h3 class="heading settled" data-level="2.2" id="what-a-multidimensional-subscript-operator-would-look-like"><span class="secno">2.2. </span><span class="content">What a multidimensional subscript operator would look like</span><a class="self-link" href="#what-a-multidimensional-subscript-operator-would-look-like"></a></h3>
   <p>This paper does not propose a multidimensional subscript operator, yet, it’s interesting to look at what it would look like.
The most logical thing to do would be to mirror the call operator syntax.</p>
<pre class="highlight"><c- k>template</c-> <c- o>&lt;</c-><c- k>typename</c-> <c- n>DataType</c-><c- o>></c->
<c- k>class</c-> <c- nc>mdspan</c-> <c- p>{</c->
  <c- k>using</c-> <c- n>reference</c-> <c- o>=</c-> <c- d>/*...*/</c-><c- p>;</c->
  <c- k>template</c-><c- o>&lt;</c-><c- b>size_t</c-><c- p>...</c-><c- o>></c->
  <c- n>reference</c-> <c- k>operator</c-><c- p>[](</c-> <c- n>IndexType</c-> <c- p>...</c-> <c- n>indices</c-> <c- p>)</c-> <c- k>const</c-> <c- k>noexcept</c-><c- p>;</c->
<c- p>};</c->

<c- n>mdspan</c-><c- o>&lt;</c-><c- b>int</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- o>></c-> <c- n>foo</c-> <c- o>=</c-> <c- d>/*....*/</c-><c- p>;</c->
<c- k>auto</c-> <c- n>bar</c-> <c- o>=</c-> <c- n>foo</c-><c- p>[</c-><c- mi>0</c-><c- p>,</c-> <c- mi>1</c-><c- p>,</c-> <c- mi>2</c-><c- p>];</c->
</pre>
   <p>This syntax resembles that of a call operator, but with the proper semantics.
A similar syntax can be found in popular languages such as Python, D and Ruby.</p>
   <h2 class="heading settled" data-level="3" id="impact-on-existing-code-bases"><span class="secno">3. </span><span class="content">Impact on existing code bases</span><a class="self-link" href="#impact-on-existing-code-bases"></a></h2>
   <p>We analyzed several large open source codebases and did not find a significant use of this pattern. <a href="https://github.com/cor3ntin/clang-tools-extra/tree/detect-comma-in-subscript">The tool used</a> is available
on Github and automatic refactoring of large code bases is possible.
In all cases, <code class="highlight"><c- n>array</c-><c- p>[</c-><c- n>x</c-><c- p>,</c-><c- n>y</c-><c- p>,</c-><c- n>z</c-><c- p>]</c-></code> can be refactored in <code class="highlight"><c- n>array</c-><c- p>[(</c-><c- n>x</c-><c- p>,</c-><c- n>y</c-><c- p>,</c-><c- n>z</c-><c- p>)]</c-></code> without alteration of semantics or behavior.</p>
   <p>The codebases analyzed include the Linux kernel, Chromium, the LLVM project and the entirety of the Boost test suite.
The only instances found were in Boost’s "Spirit Classic" library (deprecated since 2009).
A documentation of the offending syntax can be found <a href="https://www.boost.org/doc/libs/1_35_0/libs/spirit/doc/switch_parser.html">here</a>.</p>
   <h2 class="heading settled" data-level="4" id="alternative-approaches"><span class="secno">4. </span><span class="content">Alternative approaches</span><a class="self-link" href="#alternative-approaches"></a></h2>
   <h3 class="heading settled" data-level="4.1" id="allow-comma-expression-only-in-c-arrays"><span class="secno">4.1. </span><span class="content">Allow comma expression only in C arrays</span><a class="self-link" href="#allow-comma-expression-only-in-c-arrays"></a></h3>
   <p>To maintain compatibility with C, it would be possible to deprecate the use of the comma operator only in overloaded operators.
Example:</p>
<pre class="highlight"><c- b>int</c-> <c- n>c_array</c-><c- p>[</c-><c- mi>1</c-><c- p>];</c->
<c- n>c_array</c-><c- p>[</c-><c- mi>1</c-><c- p>,</c-><c- mi>0</c-><c- p>];</c->   <c- c1>// </c-><b><c- c1>not</c-></b><c- c1> deprecated</c->

<c- n>std</c-><c- o>::</c-><c- n>array</c-><c- o>&lt;</c-><c- b>int</c-><c- p>,</c-> <c- mi>1</c-><c- o>></c-> <c- n>cpp_array</c-><c- p>;</c->
<c- n>cpp_array</c-><c- p>[</c-><c- mi>1</c-><c- p>,</c-><c- mi>0</c-><c- p>];</c->   <c- c1>// </c-><b><c- c1>deprecated</c-></b>
</pre>
   <p>However, this would probably lead to more confusion for a feature that is virtually unused.</p>
   <h3 class="heading settled" data-level="4.2" id="alternative-syntax-for-multidimensional-subscript-expressions"><span class="secno">4.2. </span><span class="content">Alternative syntax for multidimensional subscript expressions</span><a class="self-link" href="#alternative-syntax-for-multidimensional-subscript-expressions"></a></h3>
   <p>It has been proposed that <code class="highlight"><c- n>array</c-><c- p>[</c-><c- n>x</c-><c- p>][</c-><c- n>y</c-><c- p>]</c-></code> should be equivalent to <code class="highlight"><c- n>array</c-><c- p>.</c-><c- k>operator</c-><c- p>[](</c-><c- n>x</c-><c- p>,</c-> <c- n>y</c-><c- p>);</c-></code></p>
<pre class="highlight"><c- n>mdspan</c-><c- o>&lt;</c-><c- b>int</c-><c- p>,</c-> <c- n>array_property</c-><c- o>::</c-><c- n>dimension</c-><c- o>&lt;</c-><c- mi>2</c-><c- p>,</c-><c- mi>3</c-><c- o>>></c-> <c- n>foo</c-><c- p>;</c->
<c- k>auto</c-> <c- n>x</c-> <c- o>=</c-> <c- n>foo</c-><c- p>[</c-><c- mi>0</c-><c- p>][</c-><c- mi>0</c-><c- p>];</c-> <c- c1>//equivalent to foo(0, 0);</c->
</pre>
   <p>However, it’s easy to imagine a scenario such that <code class="highlight"><c- p>(</c-><c- n>array</c-><c- p>[</c-><c- n>x</c-><c- p>])[</c-><c- n>y</c-><c- p>]</c-></code> would be a valid expression.
For example:</p>
<pre class="highlight"><c- k>struct</c-> <c- n>row</c-> <c- p>{</c->
    <c- n>Foo</c-> <c- o>&amp;</c-> <c- k>operator</c-><c- p>[</c-><c- b>size_t</c-><c- p>];</c->
<c- p>};</c->
<c- k>struct</c-> <c- n>grid</c-> <c- p>{</c->
    <c- n>row</c-> <c- o>&amp;</c-> <c- k>operator</c-><c- p>[</c-><c- b>size_t</c-><c- p>]</c-> <c- k>const</c-><c- p>;</c->
    <c- k>const</c-> <c- n>Foo</c-> <c- o>&amp;</c-> <c- k>operator</c-><c- p>[</c-><c- b>size_t</c-><c- p>,</c-> <c- b>size_t</c-><c- p>]</c-> <c- k>const</c-><c- p>;</c->
<c- p>};</c->
<c- n>grid</c-> <c- n>g</c-><c- p>;</c->
</pre>
   <p>In this somewhat artificial example, <code class="highlight"><c- n>g</c-><c- p>[</c-><c- mi>0</c-><c- p>][</c-><c- mi>0</c-><c- p>]</c-></code> and <code class="highlight"><c- p>(</c-><c- n>g</c-><c- p>[</c-><c- mi>0</c-><c- p>])[</c-><c- mi>0</c-><c- p>]</c-></code> would be 2 valid, different expressions,
which is confusing.
Moreover, making this syntax compatible with pack expansion and fold expressions would certainly prove challenging.</p>
   <p>On the other hand, this syntax mirror the usage of multidimensional C arrays and is also popular in
other languages, such as Perl.</p>
   <h3 class="heading settled" data-level="4.3" id="other-comma-expressions"><span class="secno">4.3. </span><span class="content">Other comma expressions</span><a class="self-link" href="#other-comma-expressions"></a></h3>
   <p>Early feedback on this paper suggested we might want to deprecate comma expressions in more contexts.
While the authors of this paper are not suggesting that, for completeness, we analyzed a few open source projects.</p>
   <p>Below are tables of contexts in which comma expressions are found in various open source projects.
The data was generated with the clang-tidy. It is meant to give a rough idea of the ways comma expressions are used
and does not pretend to be completely accurate.</p>
   <p>We provide two tables.
The first counts each expression encountered throughout a project exactly one and as such gives an idea of the amount of code that would
have to be modified to conform to some eventual deprecation.</p>
   <h4 class="heading settled" data-level="4.3.1" id="without-duplication-caused-by-headers-included-multiple-times-throughout-a-project"><span class="secno">4.3.1. </span><span class="content">Without duplication caused by headers included multiple times throughout a project</span><a class="self-link" href="#without-duplication-caused-by-headers-included-multiple-times-throughout-a-project"></a></h4>
   <table class="data-table">
    <thead>
     <tr>
      <th>Parent Expression
      <th>Boost
      <th>Chromium
      <th>Firefox
      <th>Kernel
      <th>Libreoffice
      <th>LLVM
      <th>Qt
      <th>
      <th><small>Estimated LOC affected*</small>
    <tbody>
     <tr>
      <td>ParenExpr
      <td>958
      <td>7717
      <td>4360
      <td>72
      <td>9375
      <td>70
      <td>1494
      <td>24046
      <td> <small> 0.030%-0.080% </small> 
     <tr>
      <td>ForStmt
      <td>764
      <td>2916
      <td>1461
      <td>565
      <td>3275
      <td>919
      <td>2616
      <td>12516
      <td> <small> 0.016%-0.042% </small> 
     <tr>
      <td>CompoundStmt
      <td>190
      <td>239
      <td>62
      <td>12
      <td>182
      <td>4
      <td>63
      <td>752
      <td> <small> 0.001%-0.003% </small> 
     <tr>
      <td>ReturnStmt
      <td>160
      <td>329
      <td>53
      <td>-
      <td>53
      <td>6
      <td>92
      <td>693
      <td> <small> 0.001%-0.002% </small> 
     <tr>
      <td>WhileStmt
      <td>69
      <td>19
      <td>4
      <td>-
      <td>66
      <td>-
      <td>14
      <td>172
      <td>~
     <tr>
      <td>IfStmt
      <td>31
      <td>51
      <td>11
      <td>-
      <td>30
      <td>1
      <td>-
      <td>124
      <td>~
     <tr>
      <td>ConditionalOperator
      <td>12
      <td>17
      <td>18
      <td>-
      <td>36
      <td>-
      <td>17
      <td>100
      <td>~
     <tr>
      <td>CaseStmt
      <td>-
      <td>7
      <td>-
      <td>-
      <td>20
      <td>-
      <td>-
      <td>27
      <td>~
     <tr>
      <td>DoStmt
      <td>1
      <td>10
      <td>1
      <td>-
      <td>1
      <td>-
      <td>-
      <td>13
      <td>~
     <tr>
      <td>CXXStaticCastExpr
      <td>5
      <td>-
      <td>-
      <td>-
      <td>-
      <td>-
      <td>-
      <td>5
      <td>~
     <tr class="array_row">
      <td>ArraySubscriptExpr
      <td>1<sup><a href="#fn1" id="ref1">1</a></sup>
      <td>-
      <td>-
      <td>-
      <td>-
      <td>-
      <td>-
      <td>1<sup><a href="#fn1" id="ref1①">1</a></sup>
      <td>~
     <tr>
      <td>DefaultStmt
      <td>-
      <td>-
      <td>-
      <td>-
      <td>1
      <td>-
      <td>-
      <td>1
      <td>~
   </table>
   <p><b>Estimated 30 to 80 millions LOC compiled. This is a back of the envelop calculation meant to be an order of magnetude rather that a meaningful, accurate value</b>.</p>
   <h4 class="heading settled" data-level="4.3.2" id="non-deduplicated-results"><span class="secno">4.3.2. </span><span class="content">Non-Deduplicated results.</span><a class="self-link" href="#non-deduplicated-results"></a></h4>
   <p>This second table represents the number of warnings that would be emitted following some eventual deprecation.</p>
   <table class="data-table">
    <thead>
     <tr>
      <th>Parent Expression
      <th>Boost
      <th>Chromium
      <th>Firefox
      <th>Kernel
      <th>Libreoffice
      <th>LLVM
      <th>Qt
      <th>
    <tbody>
     <tr>
      <td>ParenExpr
      <td>167038
      <td>69625
      <td>100295
      <td>924
      <td>55551
      <td>1451
      <td>6045
      <td>400929
     <tr>
      <td>ForStmt
      <td>106372
      <td>139460
      <td>99515
      <td>4114
      <td>12876
      <td>13343
      <td>11464
      <td>387144
     <tr>
      <td>ReturnStmt
      <td>55417
      <td>20353
      <td>1253
      <td>-
      <td>455
      <td>46
      <td>17636
      <td>95160
     <tr>
      <td>WhileStmt
      <td>11179
      <td>33
      <td>10
      <td>-
      <td>66
      <td>-
      <td>8822
      <td>20110
     <tr>
      <td>ConditionalOperator
      <td>11894
      <td>17
      <td>18
      <td>-
      <td>182
      <td>-
      <td>17
      <td>12128
     <tr>
      <td>CompoundStmt
      <td>8995
      <td>335
      <td>254
      <td>12
      <td>341
      <td>4
      <td>314
      <td>10255
     <tr>
      <td>IfStmt
      <td>504
      <td>54
      <td>26
      <td>-
      <td>359
      <td>1
      <td>-
      <td>944
     <tr>
      <td>CXXStaticCastExpr
      <td>653
      <td>-
      <td>-
      <td>-
      <td>-
      <td>-
      <td>-
      <td>653
     <tr>
      <td>DoStmt
      <td>18
      <td>14
      <td>34
      <td>-
      <td>1
      <td>-
      <td>-
      <td>67
     <tr>
      <td>CaseStmt
      <td>-
      <td>7
      <td>-
      <td>-
      <td>35
      <td>-
      <td>-
      <td>42
     <tr class="array_row">
      <td>ArraySubscriptExpr
      <td>4 <sup><a href="#fn1" id="ref1②">1</a></sup>
      <td>-
      <td>-
      <td>-
      <td>-
      <td>-
      <td>-
      <td>4<sup><a href="#fn1" id="ref1③">1</a></sup>
     <tr>
      <td>DefaultStmt
      <td>-
      <td>-
      <td>-
      <td>-
      <td>4
      <td>-
      <td>-
      <td>4
   </table>
   <p><sup id="fn1">1. The only instances found where in boost’s "Spirit Classic" library (deprecated since 2009).A documentation of the offending syntax can be found <a href="https://www.boost.org/doc/libs/1_35_0/libs/spirit/doc/switch_parser.html"> here</a>.<a href="#ref1">↩</a></sup></p>
   <h2 class="heading settled" data-level="5" id="proposed-wording"><span class="secno">5. </span><span class="content">Proposed Wording</span><a class="self-link" href="#proposed-wording"></a></h2>
   <p>In annex D, add a new subclause [depr.comma.subscript]</p>
   <div class="wording-add">
    <h3 class="heading settled" data-level="5.1" id="d-comma-operator-in-subscript-expressions"><span class="secno">5.1. </span><span class="content">D.� Comma operator in subscript expressions</span><a class="self-link" href="#d-comma-operator-in-subscript-expressions"></a></h3>
     A comma expression ([expr.comma]) appearing as the <em>expr-or-braced-init-list<em> of an array subscript expression ([expr.sub]) is deprecated.
[Note: A comma appearing in parenthesis is not deprecated] <br> [Example: <pre class="highlight"><c- n>a</c-><c- p>[</c-><c- n>b</c-><c- p>,</c-><c- n>c</c-><c- p>];</c->   <c- c1>//deprecated</c->
<c- n>a</c-><c- p>[(</c-><c- n>b</c-><c- p>,</c-><c- n>c</c-><c- p>)];</c-> <c- c1>// Not deprecated; equivalent to a[c] except that b is evaluated as a discarded-value expression</c->
</pre>]</em></em>
   </div>
   <em><em> <p>After 7.6.1.1 [expr.comma] ¶1 ("A postfix expression followed by an expression in square brackets is a postfix expression..."), add a paragraph</p> <div class="wording-add"> [Note: In subscript expressions, the comma operator is deprecated; see [depr.comma.subscript].] </div> <p>Add a paragraph after 7.6.19 [expr.sub] ¶2 ("In contexts where comma is given a special meaning, ...")</p> <div class="wording-add"> [Note: In subscript expressions, the comma operator is deprecated; see [depr.comma-subscript].] </div> <h2 class="heading settled" data-level="6" id="acknowledgments"><span class="secno">6. </span><span class="content">Acknowledgments</span><a class="self-link" href="#acknowledgments"></a></h2> Thanks to Martin Hořeňovský who computed some of the statistics on comma operator usages presented in this paper. <p>Thanks to Titus Winters and JF Bastien who provided useful feedbacks and criticism.</p> </em></em>
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      on = !document.body.classList.contains('toc-sidebar');
    }

    /* Don’t scroll to compensate for the ToC if we’re above it already. */
    var headY = 0;
    var head = document.querySelector('.head');
    if (head) {
      // terrible approx of "top of ToC"
      headY += head.offsetTop + head.offsetHeight;
    }
    var skipScroll = window.scrollY < headY;

    var toggle = document.getElementById('toc-toggle');
    var tocNav = document.getElementById('toc');
    if (on) {
      var tocHeight = tocNav.offsetHeight;
      document.body.classList.add('toc-sidebar');
      document.body.classList.remove('toc-inline');
      toggle.innerHTML = collapseSidebarText;
      if (!skipScroll) {
        window.scrollBy(0, 0 - tocHeight);
      }
      tocNav.focus();
      sidebarMedia.addListener(autoToggle); // auto-collapse when out of room
    }
    else {
      document.body.classList.add('toc-inline');
      document.body.classList.remove('toc-sidebar');
      toggle.innerHTML = expandSidebarText;
      if (!skipScroll) {
        window.scrollBy(0, tocNav.offsetHeight);
      }
      if (toggle.matches(':hover')) {
        /* Unfocus button when not using keyboard navigation,
           because I don’t know where else to send the focus. */
        toggle.blur();
      }
    }
  }

  function createSidebarToggle() {
    /* Create the sidebar toggle in JS; it shouldn’t exist when JS is off. */
    var toggle = document.createElement('a');
      /* This should probably be a button, but appearance isn’t standards-track.*/
    toggle.id = 'toc-toggle';
    toggle.class = 'toc-toggle';
    toggle.href = '#toc';
    toggle.innerHTML = collapseSidebarText;

    sidebarMedia.addListener(autoToggle);
    var toggler = function(e) {
      e.preventDefault();
      sidebarMedia.removeListener(autoToggle); // persist explicit off states
      toggleSidebar();
      return false;
    }
    toggle.addEventListener('click', toggler, false);


    /* Get <nav id=toc-nav>, or make it if we don’t have one. */
    var tocNav = document.getElementById('toc-nav');
    if (!tocNav) {
      tocNav = document.createElement('p');
      tocNav.id = 'toc-nav';
      /* Prepend for better keyboard navigation */
      document.body.insertBefore(tocNav, document.body.firstChild);
    }
    /* While we’re at it, make sure we have a Jump to Toc link. */
    var tocJump = document.getElementById('toc-jump');
    if (!tocJump) {
      tocJump = document.createElement('a');
      tocJump.id = 'toc-jump';
      tocJump.href = '#toc';
      tocJump.innerHTML = tocJumpText;
      tocNav.appendChild(tocJump);
    }

    tocNav.appendChild(toggle);
  }

  var toc = document.getElementById('toc');
  if (toc) {
    createSidebarToggle();
    toggleSidebar(sidebarMedia.matches);

    /* If the sidebar has been manually opened and is currently overlaying the text
       (window too small for the MQ to add the margin to body),
       then auto-close the sidebar once you click on something in there. */
    toc.addEventListener('click', function(e) {
      if(e.target.tagName.toLowerCase() == "a" && document.body.classList.contains('toc-sidebar') && !sidebarMedia.matches) {
        toggleSidebar(false);
      }
    }, false);
  }
  else {
    console.warn("Can’t find Table of Contents. Please use <nav id='toc'> around the ToC.");
  }

  /* Wrap tables in case they overflow */
  var tables = document.querySelectorAll(':not(.overlarge) > table.data, :not(.overlarge) > table.index');
  var numTables = tables.length;
  for (var i = 0; i < numTables; i++) {
    var table = tables[i];
    var wrapper = document.createElement('div');
    wrapper.className = 'overlarge';
    table.parentNode.insertBefore(wrapper, table);
    wrapper.appendChild(table);
  }

})();
</script> </em></em>
  <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-p1277">[P1277]
   <dd>Isabella Muerte. <a href="https://wg21.link/P1277">Subscripts On Parade</a>. URL: <a href="https://wg21.link/P1277">https://wg21.link/P1277</a>
  </dl>