text: <!doctype html><html lang="en">
   <head>
    <meta content="text/html; charset=utf-8" http-equiv="Content-Type">
    <title>[TITLE]</title>
    <meta content="width=device-width, initial-scale=1, shrink-to-fit=no" name="viewport">
  <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,
  	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;
  		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;
  		text-align: center;
  	}
  
  	table.data.longlastcol td:last-child,
  	table.data td.long {
  	 vertical-align: baseline;
  	 text-align: left;
  	}
  
  	table.data img {
  		vertical-align: middle;
  	}
  
  
  /*
  Alternate table alignment rules
  
  	table.data,
  	table.index {
  		text-align: center;
  	}
  
  	table.data  thead th[scope="row"],
  	table.index thead th[scope="row"] {
  		text-align: right;
  	}
  
  	table.data  tbody th:first-child,
  	table.index tbody th:first-child  {
  		text-align: right;
  	}
  
  Possible extra rowspan handling
  
  	table.data  tbody th[rowspan]:not([rowspan='1']),
  	table.index tbody th[rowspan]:not([rowspan='1']),
  	table.data  tbody td[rowspan]:not([rowspan='1']),
  	table.index tbody td[rowspan]:not([rowspan='1']) {
  		border-left: 1px solid silver;
  	}
  
  	table.data  tbody th[rowspan]:first-child,
  	table.index tbody th[rowspan]:first-child,
  	table.data  tbody td[rowspan]:first-child,
  	table.index tbody td[rowspan]:first-child{
  		border-left: 0;
  		border-right: 1px solid silver;
  	}
  */
  
  /******************************************************************************/
  /*                                  Indices                                   */
  /******************************************************************************/
  
  
  /** Table of Contents *********************************************************/
  
  	.toc a {
  		/* More spacing; use padding to make it part of the click target. */
  		padding-top: 0.1rem;
  		/* Larger, more consistently-sized click target */
  		display: block;
  		/* Reverse color scheme */
  		color: black;
  		border-color: #3980B5;
  		border-bottom-width: 3px !important;
  		margin-bottom: 0px !important;
  	}
  	.toc a:visited {
  		border-color: #054572;
  	}
  	.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;
  		line-height: 1.1rem; /* consistent spacing */
  	}
  
  	/* 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 .secno { font-size: 85%; }
  	.toc > li li li li li { font-size:   85%;    }
  	.toc > li li li li li .secno { font-size: 100%; }
  
  	/* @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 {
  			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; }
  		}
  	/* } */
  
  	@supports (display:grid) and (display:contents) {
  		/* Use #toc over .toc to override non-@supports rules. */
  		#toc {
  			display: grid;
  			align-content: start;
  			grid-template-columns: auto 1fr;
  			grid-column-gap: 1rem;
  			column-gap: 1rem;
  			grid-row-gap: .6rem;
  			row-gap: .6rem;
  		}
  		#toc h2 {
  			grid-column: 1 / -1;
  			margin-bottom: 0;
  		}
  		#toc ol,
  		#toc li,
  		#toc a {
  			display: contents;
  			/* Switch <a> to subgrid when supported */
  		}
  		#toc span {
  			margin: 0;
  		}
  		#toc > .toc > li > a > span {
  			/* The spans of the top-level list,
  			   comprising the first items of each top-level section. */
  			margin-top: 1.1rem;
  		}
  		#toc#toc .secno { /* Ugh, need more specificity to override base.css */
  			grid-column: 1;
  			width: auto;
  			margin-left: 0;
  		}
  		#toc .content {
  			grid-column: 2;
  			width: auto;
  			margin-right: 1rem;
  		}
  		#toc .content:hover {
  			background: rgba(75%, 75%, 75%, .25);
  			border-bottom: 3px solid #054572;
  			margin-bottom: -3px;
  		}
  		#toc li li li .content {
  			margin-left: 1rem;
  		}
  		#toc li li li li .content {
  			margin-left: 2rem;
  		}
  	}
  
  
  /** Index *********************************************************************/
  
  	/* Index Lists: Layout */
  	ul.index       { margin-left: 0; columns: 15em; text-indent: 1em hanging; }
  	ul.index li    { margin-left: 0; list-style: none; break-inside: avoid; }
  	ul.index li li { margin-left: 1em }
  	ul.index dl    { margin-top: 0; }
  	ul.index dt    { margin: .2em 0 .2em 20px;}
  	ul.index dd    { margin: .2em 0 .2em 40px;}
  	/* Index Lists: Typography */
  	ul.index ul,
  	ul.index dl { font-size: smaller; }
  	@media not print {
  		ul.index li span {
  			white-space: nowrap;
  			color: transparent; }
  		ul.index li a:hover + span,
  		ul.index li a:focus + span {
  			color: #707070;
  		}
  	}
  
  /** 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]) {
  		background: #f7f8f9;
  	}
  
  	/* The link in the first column in the property table (formerly a TD) */
  	table.index th:first-child a {
  		font-weight: bold;
  	}
  
  /******************************************************************************/
  /*                                    Print                                   */
  /******************************************************************************/
  
  	@media print {
  		/* Pages have their own margins. */
  		html {
  			margin: 0;
  		}
  		/* Serif for print. */
  		body {
  			font-family: serif;
  		}
  	}
  	@page {
  		margin: 1.5cm 1.1cm;
  	}
  
  /******************************************************************************/
  /*                                    Legacy                                  */
  /******************************************************************************/
  
  	/* This rule is inherited from past style sheets. No idea what it's for. */
  	.hide { display: none }
  
  
  
  /******************************************************************************/
  /*                             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 table positioning:
  		   "content column" is 50ems wide at max; less on smaller screens.
  		   Extra space (after ToC + content) is empty on the right.
  
  		   1. When table < content column, centers table in column.
  		   2. When content < table < available, left-aligns.
  		   3. When table > 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>/* style-autolinks */
  
  .css.css, .property.property, .descriptor.descriptor {
      color: #005a9c;
      font-size: inherit;
      font-family: inherit;
  }
  .css::before, .property::before, .descriptor::before {
      content: "‘";
  }
  .css::after, .property::after, .descriptor::after {
      content: "’";
  }
  .property, .descriptor {
      /* Don't wrap property and descriptor names */
      white-space: nowrap;
  }
  .type { /* CSS value <type> */
      font-style: italic;
  }
  pre .property::before, pre .property::after {
      content: "";
  }
  [data-link-type="property"]::before,
  [data-link-type="propdesc"]::before,
  [data-link-type="descriptor"]::before,
  [data-link-type="value"]::before,
  [data-link-type="function"]::before,
  [data-link-type="at-rule"]::before,
  [data-link-type="selector"]::before,
  [data-link-type="maybe"]::before {
      content: "‘";
  }
  [data-link-type="property"]::after,
  [data-link-type="propdesc"]::after,
  [data-link-type="descriptor"]::after,
  [data-link-type="value"]::after,
  [data-link-type="function"]::after,
  [data-link-type="at-rule"]::after,
  [data-link-type="selector"]::after,
  [data-link-type="maybe"]::after {
      content: "’";
  }
  
  [data-link-type].production::before,
  [data-link-type].production::after,
  .prod [data-link-type]::before,
  .prod [data-link-type]::after {
      content: "";
  }
  
  [data-link-type=element],
  [data-link-type=element-attr] {
      font-family: Menlo, Consolas, "DejaVu Sans Mono", monospace;
      font-size: .9em;
  }
  [data-link-type=element]::before { content: "<" }
  [data-link-type=element]::after  { content: ">" }
  
  [data-link-type=biblio] {
      white-space: pre;
  }</style>
  <style>/* style-counters */
  
  body {
      counter-reset: example figure issue;
  }
  .issue {
      counter-increment: issue;
  }
  .issue:not(.no-marker)::before {
      content: "Issue " counter(issue);
  }
  
  .example {
      counter-increment: example;
  }
  .example:not(.no-marker)::before {
      content: "Example " counter(example);
  }
  .invalid.example:not(.no-marker)::before,
  .illegal.example:not(.no-marker)::before {
      content: "Invalid Example" counter(example);
  }
  
  figcaption {
      counter-increment: figure;
  }
  figcaption:not(.no-marker)::before {
      content: "Figure " counter(figure) " ";
  }</style>
  <style>/* style-md-lists */
  
  /* This is a weird hack for me not yet following the commonmark spec
     regarding paragraph and lists. */
  [data-md] > :first-child {
      margin-top: 0;
  }
  [data-md] > :last-child {
      margin-bottom: 0;
  }</style>
  <style>/* style-selflinks */
  
  .heading, .issue, .note, .example, li, dt {
      position: relative;
  }
  a.self-link {
      position: absolute;
      top: 0;
      left: calc(-1 * (3.5rem - 26px));
      width: calc(3.5rem - 26px);
      height: 2em;
      text-align: center;
      border: none;
      transition: opacity .2s;
      opacity: .5;
  }
  a.self-link:hover {
      opacity: 1;
  }
  .heading > a.self-link {
      font-size: 83%;
  }
  li > a.self-link {
      left: calc(-1 * (3.5rem - 26px) - 2em);
  }
  dfn > a.self-link {
      top: auto;
      left: auto;
      opacity: 0;
      width: 1.5em;
      height: 1.5em;
      background: gray;
      color: white;
      font-style: normal;
      transition: opacity .2s, background-color .2s, color .2s;
  }
  dfn:hover > a.self-link {
      opacity: 1;
  }
  dfn > a.self-link:hover {
      color: black;
  }
  
  a.self-link::before            { content: "¶"; }
  .heading > a.self-link::before { content: "§"; }
  dfn > a.self-link::before      { content: "#"; }</style>
   <body class="h-entry">
    <div class="head">
     <p data-fill-with="logo"></p>
     <h1 class="p-name no-ref allcaps" id="title">[TITLE]</h1>
     <h2 class="no-num no-toc no-ref heading settled" id="subtitle"><span class="content">, <time class="dt-updated" datetime="1970-01-01">1 January 1970</time></span></h2>
     <div data-fill-with="spec-metadata">
      <dl></dl>
     </div>
     <div data-fill-with="warning"></div>
     <p class="copyright" data-fill-with="copyright"><a href="http://creativecommons.org/publicdomain/zero/1.0/" rel="license"><img alt="CC0" src="https://licensebuttons.net/p/zero/1.0/80x15.png"></a> To the extent possible under law, the editors have waived all copyright
  and related or neighboring rights to this work.
  In addition, as of 1 January 1970,
  the editors have made this specification available under the <a href="http://www.openwebfoundation.org/legal/the-owf-1-0-agreements/owfa-1-0" rel="license">Open Web Foundation Agreement Version 1.0</a>,
  which is available at http://www.openwebfoundation.org/legal/the-owf-1-0-agreements/owfa-1-0.
  Parts of this work may be from another specification document.  If so, those parts are instead covered by the license of that specification document. </p>
     <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>
      [ABSTRACT] 
    </div>
    <div data-fill-with="at-risk"></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="#conformance"><span class="secno"></span> <span class="content"> Conformance</span></a>
      <li>
       <a href="#references"><span class="secno"></span> <span class="content">References</span></a>
       <ol class="toc">
        <li><a href="#normative"><span class="secno"></span> <span class="content">Normative References</span></a>
       </ol>
     </ol>
    </nav>
    <main>
     <p>Failure!
  I’m nested two deep,
  so the only way to reach me is if the nested include’s path
  was resolved relative to its own location,
  rather than the parent doc’s location!</p>
    </main>
    <div data-fill-with="conformance">
     <h2 class="no-ref no-num heading settled" id="conformance"><span class="content"> Conformance</span></h2>
     <p> Conformance requirements are expressed with a combination of descriptive assertions and RFC 2119 terminology.
              The key words “MUST”, “MUST NOT”, “REQUIRED”, “SHALL”, “SHALL NOT”, “SHOULD”, “SHOULD NOT”, “RECOMMENDED”, “MAY”, and “OPTIONAL”
              in the normative parts of this document
              are to be interpreted as described in RFC 2119.
              However, for readability,
              these words do not appear in all uppercase letters in this specification. </p>
     <p> All of the text of this specification is normative
              except sections explicitly marked as non-normative, examples, and notes. <a data-link-type="biblio" href="#biblio-rfc2119">[RFC2119]</a> </p>
     <p> Examples in this specification are introduced with the words “for example”
              or are set apart from the normative text with <code>class="example"</code>, like this: </p>
     <div class="example" id="example-example"><a class="self-link" href="#example-example"></a> This is an example of an informative example. </div>
     <p> Informative notes begin with the word “Note”
              and are set apart from the normative text with <code>class="note"</code>, like this: </p>
     <p class="note" role="note"> Note, this is an informative note. </p>
    </div>
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                            + '<span>Pop Out Sidebar</span>';
    var tocJumpText         = '<span aria-hidden="true">↑</span> '
                            + '<span>Jump to Table of Contents</span>';
  
    var sidebarMedia = window.matchMedia('screen and (min-width: 78em)');
    var autoToggle   = function(e){ toggleSidebar(e.matches) };
    if(sidebarMedia.addListener) {
      sidebarMedia.addListener(autoToggle);
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      /* Don’t scroll to compensate for the ToC if we’re above it already. */
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      var toggle = document.getElementById('toc-toggle');
      var tocNav = document.getElementById('toc');
      if (on) {
        var tocHeight = tocNav.offsetHeight;
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          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>
    <h2 class="no-num no-ref heading settled" id="references"><span class="content">References</span></h2>
    <h3 class="no-num no-ref heading settled" id="normative"><span class="content">Normative References</span></h3>
    <dl>
     <dt id="biblio-rfc2119">[RFC2119]
     <dd>S. Bradner. <a href="https://tools.ietf.org/html/rfc2119">Key words for use in RFCs to Indicate Requirement Levels</a>. March 1997. Best Current Practice. URL: <a href="https://tools.ietf.org/html/rfc2119">https://tools.ietf.org/html/rfc2119</a>
    </dl>