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1620 lines
94 KiB
1620 lines
94 KiB
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
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<html lang="en-US-x-Hixie" ><head><title>4.8 Embedded content — HTML5 </title><style type="text/css">
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pre { margin-left: 2em; white-space: pre-wrap; }
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h2 { margin: 3em 0 1em 0; }
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h3 { margin: 2.5em 0 1em 0; }
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h4 { margin: 2.5em 0 0.75em 0; }
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h5, h6 { margin: 2.5em 0 1em; }
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h1 + h2, h1 + h2 + h2 { margin: 0.75em 0 0.75em; }
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h2 + h3, h3 + h4, h4 + h5, h5 + h6 { margin-top: 0.5em; }
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p { margin: 1em 0; }
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hr:not(.top) { display: block; background: none; border: none; padding: 0; margin: 2em 0; height: auto; }
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dl, dd { margin-top: 0; margin-bottom: 0; }
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dt { margin-top: 0.75em; margin-bottom: 0.25em; clear: left; }
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dt + dt { margin-top: 0; }
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dd dt { margin-top: 0.25em; margin-bottom: 0; }
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dd p { margin-top: 0; }
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dd dl + p { margin-top: 1em; }
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dd table + p { margin-top: 1em; }
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p + * > li, dd li { margin: 1em 0; }
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dt, dfn { font-weight: bold; font-style: normal; }
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dt dfn { font-style: italic; }
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pre, code { font-size: inherit; font-family: monospace; font-variant: normal; }
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pre strong { color: black; font: inherit; font-weight: bold; background: yellow; }
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pre em { font-weight: bolder; font-style: normal; }
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@media screen { code { color: orangered; } code :link, code :visited { color: inherit; } }
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var sub { vertical-align: bottom; font-size: smaller; position: relative; top: 0.1em; }
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table { border-collapse: collapse; border-style: hidden hidden none hidden; }
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table thead, table tbody { border-bottom: solid; }
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table tbody th:first-child { border-left: solid; }
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table tbody th { text-align: left; }
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table td, table th { border-left: solid; border-right: solid; border-bottom: solid thin; vertical-align: top; padding: 0.2em; }
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blockquote { margin: 0 0 0 2em; border: 0; padding: 0; font-style: italic; }
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.bad, .bad *:not(.XXX) { color: gray; border-color: gray; background: transparent; }
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.matrix, .matrix td { border: none; text-align: right; }
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.matrix { margin-left: 2em; }
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.dice-example { border-collapse: collapse; border-style: hidden solid solid hidden; border-width: thin; margin-left: 3em; }
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.dice-example caption { width: 30em; font-size: smaller; font-style: italic; padding: 0.75em 0; text-align: left; }
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.dice-example td, .dice-example th { border: solid thin; width: 1.35em; height: 1.05em; text-align: center; padding: 0; }
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.toc dfn, h1 dfn, h2 dfn, h3 dfn, h4 dfn, h5 dfn, h6 dfn { font: inherit; }
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img.extra { float: right; }
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pre.idl { border: solid thin; background: #EEEEEE; color: black; padding: 0.5em 1em; }
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pre.idl :link, pre.idl :visited { color: inherit; background: transparent; }
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pre.css { border: solid thin; background: #FFFFEE; color: black; padding: 0.5em 1em; }
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pre.css:first-line { color: #AAAA50; }
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dl.domintro { color: green; margin: 2em 0 2em 2em; padding: 0.5em 1em; border: none; background: #DDFFDD; }
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hr + dl.domintro, div.impl + dl.domintro { margin-top: 2.5em; margin-bottom: 1.5em; }
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dl.domintro dt, dl.domintro dt * { color: black; text-decoration: none; }
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dl.domintro dd { margin: 0.5em 0 1em 2em; padding: 0; }
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dl.domintro dd p { margin: 0.5em 0; }
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dl.switch { padding-left: 2em; }
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dl.switch > dt { text-indent: -1.5em; }
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dl.switch > dt:before { content: '\21AA'; padding: 0 0.5em 0 0; display: inline-block; width: 1em; text-align: right; line-height: 0.5em; }
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dl.triple { padding: 0 0 0 1em; }
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dl.triple dt, dl.triple dd { margin: 0; display: inline }
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dl.triple dt:after { content: ':'; }
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dl.triple dd:after { content: '\A'; white-space: pre; }
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.diff-old { text-decoration: line-through; color: silver; background: transparent; }
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.diff-chg, .diff-new { text-decoration: underline; color: green; background: transparent; }
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a .diff-new { border-bottom: 1px blue solid; }
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h2 { page-break-before: always; }
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h1, h2, h3, h4, h5, h6 { page-break-after: avoid; }
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h1 + h2, hr + h2.no-toc { page-break-before: auto; }
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p > span:not([title=""]):not([class="XXX"]):not([class="impl"]):not([class="note"]),
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li > span:not([title=""]):not([class="XXX"]):not([class="impl"]):not([class="note"]), { border-bottom: solid #9999CC; }
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div.head { margin: 0 0 1em; padding: 1em 0 0 0; }
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div.head p { margin: 0; }
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div.head h1 { margin: 0; }
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div.head .logo { float: right; margin: 0 1em; }
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div.head .logo img { border: none } /* remove border from top image */
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div.head dl { margin: 1em 0; }
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div.head p.copyright, div.head p.alt { font-size: x-small; font-style: oblique; margin: 0; }
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body > .toc > li { margin-top: 1em; margin-bottom: 1em; }
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body > .toc.brief > li { margin-top: 0.35em; margin-bottom: 0.35em; }
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body > .toc > li > * { margin-bottom: 0.5em; }
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body > .toc > li > * > li > * { margin-bottom: 0.25em; }
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.toc, .toc li { list-style: none; }
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.brief { margin-top: 1em; margin-bottom: 1em; line-height: 1.1; }
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.brief li { margin: 0; padding: 0; }
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.brief li p { margin: 0; padding: 0; }
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.category-list { margin-top: -0.75em; margin-bottom: 1em; line-height: 1.5; }
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.category-list::before { content: '\21D2\A0'; font-size: 1.2em; font-weight: 900; }
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.category-list li { display: inline; }
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.category-list li:not(:last-child)::after { content: ', '; }
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.category-list li > span, .category-list li > a { text-transform: lowercase; }
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.category-list li * { text-transform: none; } /* don't affect <code> nested in <a> */
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.XXX { color: #E50000; background: white; border: solid red; padding: 0.5em; margin: 1em 0; }
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.XXX > :first-child { margin-top: 0; }
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p .XXX { line-height: 3em; }
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.annotation { border: solid thin black; background: #0C479D; color: white; position: relative; margin: 8px 0 20px 0; }
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.annotation:before { position: absolute; left: 0; top: 0; width: 100%; height: 100%; margin: 6px -6px -6px 6px; background: #333333; z-index: -1; content: ''; }
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.annotation :link, .annotation :visited { color: inherit; }
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.annotation :link:hover, .annotation :visited:hover { background: transparent; }
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.annotation span { border: none ! important; }
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.note { color: green; background: transparent; font-family: sans-serif; }
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.warning { color: red; background: transparent; }
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.note, .warning { font-weight: bolder; font-style: italic; }
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p.note, div.note { padding: 0.5em 2em; }
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span.note { padding: 0 2em; }
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.note p:first-child, .warning p:first-child { margin-top: 0; }
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.note p:last-child, .warning p:last-child { margin-bottom: 0; }
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.warning:before { font-style: normal; }
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p.note:before { content: 'Note: '; }
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p.warning:before { content: '\26A0 Warning! '; }
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.bookkeeping:before { display: block; content: 'Bookkeeping details'; font-weight: bolder; font-style: italic; }
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.bookkeeping { font-size: 0.8em; margin: 2em 0; }
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.bookkeeping p { margin: 0.5em 2em; display: list-item; list-style: square; }
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.bookkeeping dt { margin: 0.5em 2em 0; }
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.bookkeeping dd { margin: 0 3em 0.5em; }
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h4 { position: relative; z-index: 3; }
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h4 + .element, h4 + div + .element { margin-top: -2.5em; padding-top: 2em; }
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.element {
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background: #EEEEFF;
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color: black;
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margin: 0 0 1em 0.15em;
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padding: 0 1em 0.25em 0.75em;
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border-left: solid #9999FF 0.25em;
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position: relative;
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z-index: 1;
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}
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.element:before {
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position: absolute;
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z-index: 2;
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top: 0;
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left: -1.15em;
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height: 2em;
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width: 0.9em;
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background: #EEEEFF;
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content: ' ';
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border-style: none none solid solid;
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border-color: #9999FF;
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border-width: 0.25em;
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}
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.example { display: block; color: #222222; background: #FCFCFC; border-left: double; margin-left: 2em; padding-left: 1em; }
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td > .example:only-child { margin: 0 0 0 0.1em; }
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ul.domTree, ul.domTree ul { padding: 0 0 0 1em; margin: 0; }
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ul.domTree li { padding: 0; margin: 0; list-style: none; position: relative; }
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ul.domTree li li { list-style: none; }
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ul.domTree li:first-child::before { position: absolute; top: 0; height: 0.6em; left: -0.75em; width: 0.5em; border-style: none none solid solid; content: ''; border-width: 0.1em; }
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ul.domTree li:not(:last-child)::after { position: absolute; top: 0; bottom: -0.6em; left: -0.75em; width: 0.5em; border-style: none none solid solid; content: ''; border-width: 0.1em; }
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ul.domTree span { font-style: italic; font-family: serif; }
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ul.domTree .t1 code { color: purple; font-weight: bold; }
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ul.domTree .t2 { font-style: normal; font-family: monospace; }
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ul.domTree .t2 .name { color: black; font-weight: bold; }
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ul.domTree .t2 .value { color: blue; font-weight: normal; }
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ul.domTree .t3 code, .domTree .t4 code, .domTree .t5 code { color: gray; }
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ul.domTree .t7 code, .domTree .t8 code { color: green; }
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ul.domTree .t10 code { color: teal; }
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body.dfnEnabled dfn { cursor: pointer; }
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.dfnPanel {
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display: inline;
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position: absolute;
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z-index: 10;
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height: auto;
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width: auto;
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padding: 0.5em 0.75em;
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font: small sans-serif, Droid Sans Fallback;
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background: #DDDDDD;
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color: black;
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border: outset 0.2em;
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}
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.dfnPanel * { margin: 0; padding: 0; font: inherit; text-indent: 0; }
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.dfnPanel :link, .dfnPanel :visited { color: black; }
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.dfnPanel p { font-weight: bolder; }
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.dfnPanel * + p { margin-top: 0.25em; }
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.dfnPanel li { list-style-position: inside; }
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#configUI { position: absolute; z-index: 20; top: 10em; right: 1em; width: 11em; font-size: small; }
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#configUI p { margin: 0.5em 0; padding: 0.3em; background: #EEEEEE; color: black; border: inset thin; }
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#configUI p label { display: block; }
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#configUI #updateUI, #configUI .loginUI { text-align: center; }
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#configUI input[type=button] { display: block; margin: auto; }
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fieldset { margin: 1em; padding: 0.5em 1em; }
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fieldset > legend + * { margin-top: 0; }
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fieldset > :last-child { margin-bottom: 0; }
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fieldset p { margin: 0.5em 0; }
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.stability {
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position: fixed;
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bottom: 0;
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left: 0; right: 0;
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margin: 0 auto 0 auto !important;
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z-index: 1000;
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width: 50%;
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background: maroon; color: yellow;
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-webkit-border-radius: 1em 1em 0 0;
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-moz-border-radius: 1em 1em 0 0;
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border-radius: 1em 1em 0 0;
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-moz-box-shadow: 0 0 1em #500;
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-webkit-box-shadow: 0 0 1em #500;
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box-shadow: 0 0 1em red;
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padding: 0.5em 1em;
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text-align: center;
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}
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.stability strong {
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display: block;
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}
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.stability input {
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appearance: none; margin: 0; border: 0; padding: 0.25em 0.5em; background: transparent; color: black;
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position: absolute; top: -0.5em; right: 0; font: 1.25em sans-serif; text-align: center;
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}
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.stability input:hover {
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color: white;
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text-shadow: 0 0 2px black;
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}
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.stability input:active {
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padding: 0.3em 0.45em 0.2em 0.55em;
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}
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.stability :link, .stability :visited,
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.stability :link:hover, .stability :visited:hover {
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background: transparent;
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color: white;
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}
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</style><link href="data:text/css,.impl%20%7B%20display:%20none;%20%7D%0Ahtml%20%7B%20border:%20solid%20yellow;%20%7D%20.domintro:before%20%7B%20display:%20none;%20%7D" id="author" rel="alternate stylesheet" title="Author documentation only"><link href="data:text/css,.impl%20%7B%20background:%20%23FFEEEE;%20%7D%20.domintro:before%20%7B%20background:%20%23FFEEEE;%20%7D" id="highlight" rel="alternate stylesheet" title="Highlight implementation
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requirements"><link href="http://www.w3.org/StyleSheets/TR/W3C-WD" rel="stylesheet" type="text/css"><style type="text/css">
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.applies thead th > * { display: block; }
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.applies thead code { display: block; }
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.applies tbody th { whitespace: nowrap; }
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.applies td { text-align: center; }
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.applies .yes { background: yellow; }
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.matrix, .matrix td { border: hidden; text-align: right; }
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.matrix { margin-left: 2em; }
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.dice-example { border-collapse: collapse; border-style: hidden solid solid hidden; border-width: thin; margin-left: 3em; }
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.dice-example caption { width: 30em; font-size: smaller; font-style: italic; padding: 0.75em 0; text-align: left; }
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.dice-example td, .dice-example th { border: solid thin; width: 1.35em; height: 1.05em; text-align: center; padding: 0; }
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td.eg { border-width: thin; text-align: center; }
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#table-example-1 { border: solid thin; border-collapse: collapse; margin-left: 3em; }
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#table-example-1 * { font-family: "Essays1743", serif; line-height: 1.01em; }
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#table-example-1 caption { padding-bottom: 0.5em; }
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#table-example-1 thead, #table-example-1 tbody { border: none; }
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#table-example-1 th, #table-example-1 td { border: solid thin; }
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#table-example-1 th { font-weight: normal; }
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#table-example-1 td { border-style: none solid; vertical-align: top; }
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#table-example-1 th { padding: 0.5em; vertical-align: middle; text-align: center; }
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#table-example-1 tbody tr:first-child td { padding-top: 0.5em; }
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#table-example-1 tbody tr:last-child td { padding-bottom: 1.5em; }
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#table-example-1 tbody td:first-child { padding-left: 2.5em; padding-right: 0; width: 9em; }
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#table-example-1 tbody td:first-child::after { content: leader(". "); }
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#table-example-1 tbody td { padding-left: 2em; padding-right: 2em; }
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#table-example-1 tbody td:first-child + td { width: 10em; }
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#table-example-1 tbody td:first-child + td ~ td { width: 2.5em; }
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#table-example-1 tbody td:first-child + td + td + td ~ td { width: 1.25em; }
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.apple-table-examples { border: none; border-collapse: separate; border-spacing: 1.5em 0em; width: 40em; margin-left: 3em; }
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.apple-table-examples * { font-family: "Times", serif; }
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.apple-table-examples td, .apple-table-examples th { border: none; white-space: nowrap; padding-top: 0; padding-bottom: 0; }
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.apple-table-examples tbody th:first-child { border-left: none; width: 100%; }
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.apple-table-examples thead th:first-child ~ th { font-size: smaller; font-weight: bolder; border-bottom: solid 2px; text-align: center; }
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.apple-table-examples tbody th::after, .apple-table-examples tfoot th::after { content: leader(". ") }
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.apple-table-examples tbody th, .apple-table-examples tfoot th { font: inherit; text-align: left; }
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.apple-table-examples td { text-align: right; vertical-align: top; }
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.apple-table-examples.e1 tbody tr:last-child td { border-bottom: solid 1px; }
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.apple-table-examples.e1 tbody + tbody tr:last-child td { border-bottom: double 3px; }
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.apple-table-examples.e2 th[scope=row] { padding-left: 1em; }
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.apple-table-examples sup { line-height: 0; }
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.details-example img { vertical-align: top; }
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#base64-table {
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|
white-space: nowrap;
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|
font-size: 0.6em;
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|
column-width: 6em;
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|
column-count: 5;
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column-gap: 1em;
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-moz-column-width: 6em;
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|
-moz-column-count: 5;
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|
-moz-column-gap: 1em;
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-webkit-column-width: 6em;
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|
-webkit-column-count: 5;
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|
-webkit-column-gap: 1em;
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}
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#base64-table thead { display: none; }
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|
#base64-table * { border: none; }
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|
#base64-table tbody td:first-child:after { content: ':'; }
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#base64-table tbody td:last-child { text-align: right; }
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#named-character-references-table {
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|
white-space: nowrap;
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|
font-size: 0.6em;
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|
column-width: 30em;
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|
column-gap: 1em;
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-moz-column-width: 30em;
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-moz-column-gap: 1em;
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-webkit-column-width: 30em;
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-webkit-column-gap: 1em;
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}
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#named-character-references-table > table > tbody > tr > td:first-child + td,
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#named-character-references-table > table > tbody > tr > td:last-child { text-align: center; }
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#named-character-references-table > table > tbody > tr > td:last-child:hover > span { position: absolute; top: auto; left: auto; margin-left: 0.5em; line-height: 1.2; font-size: 5em; border: outset; padding: 0.25em 0.5em; background: white; width: 1.25em; height: auto; text-align: center; }
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#named-character-references-table > table > tbody > tr#entity-CounterClockwiseContourIntegral > td:first-child { font-size: 0.5em; }
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.glyph.control { color: red; }
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@font-face {
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font-family: 'Essays1743';
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src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743.ttf');
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}
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@font-face {
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font-family: 'Essays1743';
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|
font-weight: bold;
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src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743-Bold.ttf');
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}
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@font-face {
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font-family: 'Essays1743';
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|
font-style: italic;
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|
src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743-Italic.ttf');
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}
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@font-face {
|
|
font-family: 'Essays1743';
|
|
font-style: italic;
|
|
font-weight: bold;
|
|
src: url('http://www.whatwg.org/specs/web-apps/current-work/fonts/Essays1743-BoldItalic.ttf');
|
|
}
|
|
|
|
</style><style type="text/css">
|
|
.domintro:before { display: table; margin: -1em -0.5em -0.5em auto; width: auto; content: 'This box is non-normative. Implementation requirements are given below this box.'; color: black; font-style: italic; border: solid 2px; background: white; padding: 0 0.25em; }
|
|
</style><script type="text/javascript">
|
|
function getCookie(name) {
|
|
var params = location.search.substr(1).split("&");
|
|
for (var index = 0; index < params.length; index++) {
|
|
if (params[index] == name)
|
|
return "1";
|
|
var data = params[index].split("=");
|
|
if (data[0] == name)
|
|
return unescape(data[1]);
|
|
}
|
|
var cookies = document.cookie.split("; ");
|
|
for (var index = 0; index < cookies.length; index++) {
|
|
var data = cookies[index].split("=");
|
|
if (data[0] == name)
|
|
return unescape(data[1]);
|
|
}
|
|
return null;
|
|
}
|
|
</script>
|
|
<script src="link-fixup.js" type="text/javascript"></script>
|
|
<link href="style.css" rel="stylesheet"><link href="edits.html" title="4.7 Edits" rel="prev">
|
|
<link href="spec.html#contents" title="Table of contents" rel="index">
|
|
<link href="the-iframe-element.html" title="4.8.2 The iframe element" rel="next">
|
|
</head><body><div class="head" id="head">
|
|
<div id="multipage-common">
|
|
<p class="stability" id="wip"><strong>This is a work in
|
|
progress!</strong> For the latest updates from the HTML WG, possibly
|
|
including important bug fixes, please look at the <a href="http://dev.w3.org/html5/spec/Overview.html">editor's draft</a> instead.
|
|
There may also be a more
|
|
<a href="http://www.w3.org/TR/html5">up-to-date Working Draft</a>
|
|
with changes based on resolution of Last Call issues.
|
|
<input onclick="closeWarning(this.parentNode)" type="button" value="╳⃝"></p>
|
|
<script type="text/javascript">
|
|
function closeWarning(element) {
|
|
element.parentNode.removeChild(element);
|
|
var date = new Date();
|
|
date.setDate(date.getDate()+4);
|
|
document.cookie = 'hide-obsolescence-warning=1; expires=' + date.toGMTString();
|
|
}
|
|
if (getCookie('hide-obsolescence-warning') == '1')
|
|
setTimeout(function () { document.getElementById('wip').parentNode.removeChild(document.getElementById('wip')); }, 2000);
|
|
</script></div>
|
|
|
|
<p><a href="http://www.w3.org/"><img alt="W3C" height="48" src="http://www.w3.org/Icons/w3c_home" width="72"></a></p>
|
|
|
|
<h1>HTML5</h1>
|
|
</div><div>
|
|
<a href="edits.html" class="prev">4.7 Edits</a> –
|
|
<a href="spec.html#contents">Table of contents</a> –
|
|
<a href="the-iframe-element.html" class="next">4.8.2 The iframe element</a>
|
|
<ol class="toc"><li><ol><li><a href="embedded-content-1.html#embedded-content-1"><span class="secno">4.8 </span>Embedded content</a>
|
|
<ol><li><a href="embedded-content-1.html#the-img-element"><span class="secno">4.8.1 </span>The <code>img</code> element</a>
|
|
<ol><li><a href="embedded-content-1.html#alt"><span class="secno">4.8.1.1 </span>Requirements for providing text to act as an alternative for images</a>
|
|
<ol><li><a href="embedded-content-1.html#general-guidelines"><span class="secno">4.8.1.1.1 </span>General guidelines</a></li><li><a href="embedded-content-1.html#a-link-or-button-containing-nothing-but-the-image"><span class="secno">4.8.1.1.2 </span>A link or button containing nothing but the image</a></li><li><a href="embedded-content-1.html#a-phrase-or-paragraph-with-an-alternative-graphical-representation:-charts-diagrams-graphs-maps-illustrations"><span class="secno">4.8.1.1.3 </span>A phrase or paragraph with an alternative graphical representation: charts, diagrams, graphs, maps, illustrations</a></li><li><a href="embedded-content-1.html#a-short-phrase-or-label-with-an-alternative-graphical-representation:-icons-logos"><span class="secno">4.8.1.1.4 </span>A short phrase or label with an alternative graphical representation: icons, logos</a></li><li><a href="embedded-content-1.html#text-that-has-been-rendered-to-a-graphic-for-typographical-effect"><span class="secno">4.8.1.1.5 </span>Text that has been rendered to a graphic for typographical effect</a></li><li><a href="embedded-content-1.html#a-graphical-representation-of-some-of-the-surrounding-text"><span class="secno">4.8.1.1.6 </span>A graphical representation of some of the surrounding text</a></li><li><a href="embedded-content-1.html#a-purely-decorative-image-that-doesn-t-add-any-information"><span class="secno">4.8.1.1.7 </span>A purely decorative image that doesn't add any information</a></li><li><a href="embedded-content-1.html#a-group-of-images-that-form-a-single-larger-picture-with-no-links"><span class="secno">4.8.1.1.8 </span>A group of images that form a single larger picture with no links</a></li><li><a href="embedded-content-1.html#a-group-of-images-that-form-a-single-larger-picture-with-links"><span class="secno">4.8.1.1.9 </span>A group of images that form a single larger picture with links</a></li><li><a href="embedded-content-1.html#a-key-part-of-the-content"><span class="secno">4.8.1.1.10 </span>A key part of the content</a></li><li><a href="embedded-content-1.html#an-image-not-intended-for-the-user"><span class="secno">4.8.1.1.11 </span>An image not intended for the user</a></li><li><a href="embedded-content-1.html#guidance-for-markup-generators"><span class="secno">4.8.1.1.12 </span>Guidance for markup generators</a></li><li><a href="embedded-content-1.html#guidance-for-conformance-checkers"><span class="secno">4.8.1.1.13 </span>Guidance for conformance checkers</a></li></ol></li></ol></li></ol></li></ol></li></ol></div>
|
|
|
|
<h3 id="embedded-content-1"><span class="secno">4.8 </span>Embedded content</h3><h4 id="the-img-element"><span class="secno">4.8.1 </span>The <dfn><code>img</code></dfn> element</h4>
|
|
|
|
<p class="XXX annotation"><span><a href="http://www.w3.org/html/wg/tracker/issues/30">ISSUE-30</a>
|
|
(longdesc) impacts this section. Priority feedback is requested on this
|
|
issue from Last Call reviewers. In particular, reviewers are invited to
|
|
review and comment on any change proposals that are related to this issue.
|
|
See the
|
|
<a href="http://dev.w3.org/html5/status/issue-status.html">current list of open Last Call issues and change proposals</a>
|
|
maintained by the HTML Working Group chairs.</span>
|
|
|
|
</p><dl class="element"><dt>Categories</dt>
|
|
<dd><a href="content-models.html#flow-content">Flow content</a>.</dd>
|
|
<dd><a href="content-models.html#phrasing-content">Phrasing content</a>.</dd>
|
|
<dd><a href="content-models.html#embedded-content">Embedded content</a>.</dd>
|
|
<dd>If the element has a <code title="attr-hyperlink-usemap"><a href="the-map-element.html#attr-hyperlink-usemap">usemap</a></code> attribute: <a href="content-models.html#interactive-content">Interactive content</a>.</dd>
|
|
<dt>Contexts in which this element can be used:</dt>
|
|
<dd>Where <a href="content-models.html#embedded-content">embedded content</a> is expected.</dd>
|
|
<dt>Content model:</dt>
|
|
<dd>Empty.</dd>
|
|
<dt>Content attributes:</dt>
|
|
<dd><a href="elements.html#global-attributes">Global attributes</a></dd>
|
|
<dd><code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code></dd>
|
|
<dd><code title="attr-img-src"><a href="#attr-img-src">src</a></code></dd>
|
|
<dd><code title="attr-hyperlink-usemap"><a href="the-map-element.html#attr-hyperlink-usemap">usemap</a></code></dd>
|
|
<dd><code title="attr-img-ismap"><a href="#attr-img-ismap">ismap</a></code></dd>
|
|
<dd><code title="attr-dim-width"><a href="the-map-element.html#attr-dim-width">width</a></code></dd>
|
|
<dd><code title="attr-dim-height"><a href="the-map-element.html#attr-dim-height">height</a></code></dd>
|
|
<dt>DOM interface:</dt>
|
|
<dd>
|
|
<pre class="idl">[NamedConstructor=<a href="#dom-image" title="dom-image">Image</a>(),
|
|
NamedConstructor=<a href="#dom-image-w" title="dom-image-w">Image</a>(in unsigned long width),
|
|
NamedConstructor=<a href="#dom-image-wh" title="dom-image-wh">Image</a>(in unsigned long width, in unsigned long height)]
|
|
interface <dfn id="htmlimageelement">HTMLImageElement</dfn> : <a href="elements.html#htmlelement">HTMLElement</a> {
|
|
attribute DOMString <a href="#dom-img-alt" title="dom-img-alt">alt</a>;
|
|
attribute DOMString <a href="#dom-img-src" title="dom-img-src">src</a>;
|
|
attribute DOMString <a href="#dom-img-usemap" title="dom-img-useMap">useMap</a>;
|
|
attribute boolean <a href="#dom-img-ismap" title="dom-img-isMap">isMap</a>;
|
|
attribute unsigned long <a href="#dom-img-width" title="dom-img-width">width</a>;
|
|
attribute unsigned long <a href="#dom-img-height" title="dom-img-height">height</a>;
|
|
readonly attribute unsigned long <a href="#dom-img-naturalwidth" title="dom-img-naturalWidth">naturalWidth</a>;
|
|
readonly attribute unsigned long <a href="#dom-img-naturalheight" title="dom-img-naturalHeight">naturalHeight</a>;
|
|
readonly attribute boolean <a href="#dom-img-complete" title="dom-img-complete">complete</a>;
|
|
};</pre>
|
|
</dd>
|
|
</dl><p>An <code><a href="#the-img-element">img</a></code> element represents an image.</p><p>The image given by the <dfn id="attr-img-src" title="attr-img-src"><code>src</code></dfn> attribute is the
|
|
embedded content; the value of the <dfn id="attr-img-alt" title="attr-img-alt"><code>alt</code></dfn> attribute provides
|
|
equivalent content for those who cannot process images or who have
|
|
image loading disabled.</p><p>The <code title="attr-img-src"><a href="#attr-img-src">src</a></code> attribute must be
|
|
present, and must contain a <a href="urls.html#valid-non-empty-url-potentially-surrounded-by-spaces">valid non-empty URL potentially
|
|
surrounded by spaces</a> referencing a non-interactive,
|
|
optionally animated, image resource that is neither paged nor
|
|
scripted.</p><p class="note">Images can thus be static bitmaps (e.g. PNGs, GIFs,
|
|
JPEGs), single-page vector documents (single-page PDFs, XML files
|
|
with an SVG root element), animated bitmaps (APNGs, animated GIFs),
|
|
animated vector graphics (XML files with an SVG root element that
|
|
use declarative SMIL animation), and so forth. However, this also
|
|
precludes SVG files with script, multipage PDF files, interactive
|
|
MNG files, HTML documents, plain text documents, and so forth.</p><p>The requirements on the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code>
|
|
attribute's value are described <a href="#alt">in the next
|
|
section</a>.</p><p>The <code><a href="#the-img-element">img</a></code> element must not be used as a layout tool.
|
|
In particular, <code><a href="#the-img-element">img</a></code> elements should not be used to
|
|
display transparent images, as they rarely convey meaning and rarely
|
|
add anything useful to the document.</p><div class="impl">
|
|
|
|
<hr><p>An <code><a href="#the-img-element">img</a></code> is always in one of the following states:</p>
|
|
|
|
<dl><dt><dfn id="img-none" title="img-none">Unavailable</dfn></dt>
|
|
<dd>The user agent hasn't obtained any image data.</dd>
|
|
|
|
<dt><dfn id="img-inc" title="img-inc">Partially available</dfn></dt>
|
|
<dd>The user agent has obtained some of the image data.</dd>
|
|
|
|
<dt><dfn id="img-all" title="img-all">Completely available</dfn></dt>
|
|
<dd>The user agent has obtained all of the image data.</dd>
|
|
|
|
<dt><dfn id="img-error" title="img-error">Broken</dfn></dt>
|
|
<dd>The user agent has obtained all of the image data that it can,
|
|
but it cannot decode the image (e.g. the image is corrupted, or the
|
|
format is not supported, or no data could be obtained).</dd>
|
|
|
|
</dl><p>When an <code><a href="#the-img-element">img</a></code> element is either in the <a href="#img-inc" title="img-inc">partially available</a> state or in the <a href="#img-all" title="img-all">completely available</a> state, it is said to be
|
|
<dfn id="img-yes" title="img-yes">available</dfn>.</p>
|
|
|
|
<p>An <code><a href="#the-img-element">img</a></code> element is initially <a href="#img-none" title="img-none">unavailable</a>.</p>
|
|
|
|
<p>User agents may obtain images immediately or on demand.</p>
|
|
|
|
<p>A user agent that obtains images immediately must synchronously
|
|
<a href="#update-the-image-data">update the image data</a> of an <code><a href="#the-img-element">img</a></code> element
|
|
whenever that element is either created with a <code title="attr-img-src"><a href="#attr-img-src">src</a></code> attribute, or has its <code title="attr-img-src"><a href="#attr-img-src">src</a></code> attribute set, changed, or
|
|
removed.</p>
|
|
<p>A user agent that obtains images on demand must <a href="#update-the-image-data">update the
|
|
image data</a> of an <code><a href="#the-img-element">img</a></code> element whenever it needs
|
|
the image data (i.e. on demand), but only if the <code><a href="#the-img-element">img</a></code>
|
|
element has a <code title="attr-img-src"><a href="#attr-img-src">src</a></code> attribute, and
|
|
if it has not <a href="#update-the-image-data" title="update the image data">updated the image
|
|
data</a> since the last time the <code title="attr-img-src"><a href="#attr-img-src">src</a></code> attribute was set. When an
|
|
<code><a href="#the-img-element">img</a></code> element's <code title="attr-img-src"><a href="#attr-img-src">src</a></code>
|
|
attribute is changed or removed, if the user agent only obtains
|
|
images on demand, the <code><a href="#the-img-element">img</a></code> element must return to the
|
|
<a href="#img-none" title="img-none">unavailable</a> state.</p>
|
|
<p>When the user agent is to <dfn id="update-the-image-data">update the image data</dfn> of an
|
|
<code><a href="#the-img-element">img</a></code> element, it must run the following steps:</p>
|
|
|
|
<ol><li><p>Return the <code><a href="#the-img-element">img</a></code> element to the <a href="#img-none" title="img-none">unavailable</a> state.</p>
|
|
|
|
</li><li><p>If an instance of the <a href="fetching-resources.html#fetch" title="fetch">fetching</a>
|
|
algorithm is still running for this element, then abort that
|
|
algorithm, discarding any pending <a href="webappapis.html#concept-task" title="concept-task">tasks</a> generated by that
|
|
algorithm.</p></li>
|
|
|
|
<li><p>Forget the <code><a href="#the-img-element">img</a></code> element's current image data, if
|
|
any.</p></li>
|
|
|
|
<li><p>If the user agent cannot support images, or its support for
|
|
images has been disabled, then abort these steps.</p></li>
|
|
|
|
<li><p>If the element's <code title="attr-img-src"><a href="#attr-img-src">src</a></code>
|
|
attribute's value is the empty string, then set the element to the
|
|
<a href="#img-error" title="img-error">broken</a> state, <a href="webappapis.html#queue-a-task">queue a
|
|
task</a> to <a href="webappapis.html#fire-a-simple-event">fire a simple event</a> named <code title="event-error">error</code> at the <code><a href="#the-img-element">img</a></code> element,
|
|
and abort these steps.</p></li>
|
|
|
|
<li>
|
|
|
|
<p>Otherwise, <a href="urls.html#resolve-a-url" title="resolve a url">resolve</a> the value
|
|
of the element's <code title="attr-img-src"><a href="#attr-img-src">src</a></code> attribute,
|
|
relative to the element, and, if that is successful,
|
|
<a href="fetching-resources.html#fetch">fetch</a> that resource.</p>
|
|
<p>The resouce obtained in this fashion is the <code><a href="#the-img-element">img</a></code>
|
|
element's image data.</p>
|
|
|
|
<p>Fetching the image must <a href="the-end.html#delay-the-load-event">delay the load
|
|
event</a> of the element's document until the <a href="webappapis.html#concept-task" title="concept-task">task</a> that is <a href="webappapis.html#queue-a-task" title="queue a
|
|
task">queued</a> by the <a href="webappapis.html#networking-task-source">networking task source</a>
|
|
once the resource has been <a href="fetching-resources.html#fetch" title="fetch">fetched</a> (<a href="#img-load">defined below</a>) has been run.</p>
|
|
|
|
<p class="warning">This, unfortunately, can be used to perform a
|
|
rudimentary port scan of the user's local network (especially in
|
|
conjunction with scripting, though scripting isn't actually
|
|
necessary to carry out such an attack). User agents may implement
|
|
<a href="origin-0.html#origin" title="origin">cross-origin</a> access control policies
|
|
that mitigate this attack, but unfortunately such policies are
|
|
typically not compatible with existing Web content.</p>
|
|
|
|
</li>
|
|
|
|
</ol><p>Each <a href="webappapis.html#concept-task" title="concept-task">task</a> that is <a href="webappapis.html#queue-a-task" title="queue a task">queued</a> by the <a href="webappapis.html#networking-task-source">networking task
|
|
source</a> while the image is being <a href="fetching-resources.html#fetch" title="fetch">fetched</a> must set the <code><a href="#the-img-element">img</a></code> element's
|
|
state to <a href="#img-inc" title="img-inc">partially available</a> and update
|
|
the presentation of the image appropriately.</p>
|
|
|
|
<p id="img-load">The <a href="webappapis.html#concept-task" title="concept-task">task</a> that is
|
|
<a href="webappapis.html#queue-a-task" title="queue a task">queued</a> by the <a href="webappapis.html#networking-task-source">networking
|
|
task source</a> once the resource has been <a href="fetching-resources.html#fetch" title="fetch">fetched</a> must act as appropriate given the
|
|
following alternatives:</p>
|
|
|
|
<dl class="switch"><dt>If the download was successful</dt>
|
|
|
|
<dd>Set the <code><a href="#the-img-element">img</a></code> element to the <a href="#img-all" title="img-all">completely available</a> state, update the
|
|
presentation of the image appropriately, and <a href="webappapis.html#queue-a-task">queue a
|
|
task</a> to <a href="webappapis.html#fire-a-simple-event">fire a simple event</a> named <code title="event-load">load</code> at the <code><a href="#the-img-element">img</a></code>
|
|
element.</dd>
|
|
|
|
<dt>Otherwise</dt>
|
|
|
|
<dd>Set the <code><a href="#the-img-element">img</a></code> element to the <a href="#img-error" title="img-error">broken</a> state, and <a href="webappapis.html#queue-a-task">queue a
|
|
task</a> to <a href="webappapis.html#fire-a-simple-event">fire a simple event</a> named <code title="event-error">error</code> at the <code><a href="#the-img-element">img</a></code>
|
|
element.</dd>
|
|
|
|
</dl><p>If at any point the user agent discovers that the image data is
|
|
corrupted in some fatal way, or that the image is not in a supported
|
|
file format, then the user agent must set the <code><a href="#the-img-element">img</a></code>
|
|
element to the <a href="#img-error" title="img-error">broken</a> state. If the
|
|
<a href="fetching-resources.html#fetch" title="fetch">fetching</a> algorithm is still running for
|
|
this element, then the user agent must also abort that algorithm,
|
|
discarding any pending <a href="webappapis.html#concept-task" title="concept-task">tasks</a>
|
|
generated by that algorithm, and then <a href="webappapis.html#queue-a-task">queue a task</a> to
|
|
<a href="webappapis.html#fire-a-simple-event">fire a simple event</a> named <code title="event-error">error</code> at the <code><a href="#the-img-element">img</a></code>
|
|
element.</p>
|
|
|
|
<p>When an <code><a href="#the-img-element">img</a></code> element is in the <a href="#img-all" title="img-all">completely available</a> state <em>and</em> the
|
|
user agent can completely decode the media data without errors, then
|
|
the <code><a href="#the-img-element">img</a></code> element is said to be <dfn id="img-good" title="img-good">fully decodable</dfn>.</p>
|
|
|
|
<p>Whether the image is fetched successfully or not (e.g. whether
|
|
the response code was a 2xx code <a href="fetching-resources.html#concept-http-equivalent-codes" title="concept-http-equivalent-codes">or equivalent</a>) must be
|
|
ignored when determining the image's type and whether it is a valid
|
|
image.</p>
|
|
|
|
<p class="note">This allows servers to return images with error
|
|
responses, and have them displayed.</p>
|
|
|
|
<p>The user agents should apply the <a href="fetching-resources.html#content-type-sniffing:-image" title="Content-Type
|
|
sniffing: image">image sniffing rules</a> to determine the type
|
|
of the image, with the image's <a href="fetching-resources.html#content-type" title="Content-Type">associated
|
|
Content-Type headers</a> giving the <var title="">official
|
|
type</var>. If these rules are not applied, then the type of the
|
|
image must be the type given by the image's <a href="fetching-resources.html#content-type" title="Content-Type">associated Content-Type headers</a>.</p>
|
|
|
|
<p>User agents must not support non-image resources with the
|
|
<code><a href="#the-img-element">img</a></code> element (e.g. XML files whose root element is an
|
|
HTML element). User agents must not run executable code
|
|
(e.g. scripts) embedded in the image resource. User agents must only
|
|
display the first page of a multipage resource (e.g. a PDF
|
|
file). User agents must not allow the resource to act in an
|
|
interactive fashion, but should honor any animation in the
|
|
resource.</p>
|
|
|
|
<p>This specification does not specify which image types are to be
|
|
supported.</p>
|
|
|
|
<p>The <a href="webappapis.html#task-source">task source</a> for these <a href="webappapis.html#concept-task" title="concept-task">tasks</a> is the <a href="webappapis.html#dom-manipulation-task-source">DOM manipulation
|
|
task source</a>.</p>
|
|
|
|
<hr><p>What an <code><a href="#the-img-element">img</a></code> element represents depends on the <code title="attr-img-src"><a href="#attr-img-src">src</a></code> attribute and the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute.</p>
|
|
|
|
<dl class="switch"><dt>If the <code title="attr-img-src"><a href="#attr-img-src">src</a></code> attribute is set
|
|
and the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute is set to
|
|
the empty string</dt>
|
|
|
|
<dd>
|
|
|
|
<p>The image is either decorative or supplemental to the rest of
|
|
the content, redundant with some other information in the
|
|
document.</p>
|
|
|
|
<p>If the image is <a href="#img-yes" title="img-yes">available</a> and the
|
|
user agent is configured to display that image, then the element
|
|
<a href="rendering.html#represents">represents</a> the element's image data.</p>
|
|
|
|
<p>Otherwise, the element <a href="rendering.html#represents">represents</a> nothing, and may
|
|
be omitted completely from the rendering. User agents may provide
|
|
the user with a notification that an image is present but has been
|
|
omitted from the rendering.</p>
|
|
|
|
</dd>
|
|
|
|
<dt>If the <code title="attr-img-src"><a href="#attr-img-src">src</a></code> attribute is set
|
|
and the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute is set to a
|
|
value that isn't empty</dt>
|
|
|
|
<dd>
|
|
|
|
<p>The image is a key part of the content; the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute gives a textual
|
|
equivalent or replacement for the image.</p>
|
|
|
|
<p>If the image is <a href="#img-yes" title="img-yes">available</a> and the
|
|
user agent is configured to display that image, then the element
|
|
<a href="rendering.html#represents">represents</a> the element's image data.</p>
|
|
|
|
<p>Otherwise, the element <a href="rendering.html#represents">represents</a> the text given
|
|
by the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute. User
|
|
agents may provide the user with a notification that an image is
|
|
present but has been omitted from the rendering.</p>
|
|
|
|
</dd>
|
|
|
|
<dt>If the <code title="attr-img-src"><a href="#attr-img-src">src</a></code> attribute is set
|
|
and the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute is not</dt>
|
|
|
|
<dd>
|
|
|
|
<p>The image might be a key part of the content, and there is no
|
|
textual equivalent of the image available.</p>
|
|
|
|
<p class="note">In a conforming document, the absence of the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute indicates that the image
|
|
is a key part of the content but that a textual replacement for
|
|
the image was not available when the image was generated.</p>
|
|
|
|
<p>If the image is <a href="#img-yes" title="img-yes">available</a> and the
|
|
user agent is configured to display that image, then the element
|
|
<a href="rendering.html#represents">represents</a> the element's image data.</p>
|
|
|
|
<p>Otherwise, the user agent should display some sort of indicator
|
|
that there is an image that is not being rendered, and may, if
|
|
requested by the user, or if so configured, or when required to
|
|
provide contextual information in response to navigation, provide
|
|
caption information for the image, derived as follows:</p>
|
|
|
|
<ol><li><p>If the image has a <code title="attr-title"><a href="elements.html#the-title-attribute">title</a></code>
|
|
attribute whose value is not the empty string, then the value of
|
|
that attribute is the caption information; abort these
|
|
steps.</p></li>
|
|
|
|
<li><p>If the image is a descendant of a <code><a href="grouping-content.html#the-figure-element">figure</a></code>
|
|
element that has a child <code><a href="grouping-content.html#the-figcaption-element">figcaption</a></code> element, and,
|
|
ignoring the <code><a href="grouping-content.html#the-figcaption-element">figcaption</a></code> element and its descendants,
|
|
the <code><a href="grouping-content.html#the-figure-element">figure</a></code> element has no text node descendants
|
|
other than <a href="content-models.html#inter-element-whitespace">inter-element whitespace</a>, and no
|
|
<a href="content-models.html#embedded-content">embedded content</a> descendant other than the
|
|
<code><a href="#the-img-element">img</a></code> element, then the contents of the first such
|
|
<code><a href="grouping-content.html#the-figcaption-element">figcaption</a></code> element are the caption information;
|
|
abort these steps.</p></li>
|
|
|
|
</ol></dd>
|
|
|
|
<dt>If the <code title="attr-img-src"><a href="#attr-img-src">src</a></code> attribute is not
|
|
set and either the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute
|
|
is set to the empty string or the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute is not set at all</dt>
|
|
|
|
<dd>
|
|
|
|
<p>The element <a href="rendering.html#represents">represents</a> nothing.</p>
|
|
|
|
</dd>
|
|
|
|
<dt>Otherwise</dt>
|
|
|
|
<dd>
|
|
|
|
<p>The element <a href="rendering.html#represents">represents</a> the text given by the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute.</p>
|
|
|
|
</dd>
|
|
|
|
</dl><p>The <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute does not
|
|
represent advisory information. User agents must not present the
|
|
contents of the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute in
|
|
the same way as content of the <code title="attr-title"><a href="elements.html#the-title-attribute">title</a></code>
|
|
attribute.</p>
|
|
|
|
<p>User agents may always provide the user with the option to
|
|
display any image, or to prevent any image from being
|
|
displayed.
|
|
|
|
|
|
</p>
|
|
|
|
<p class="warning">While user agents are encouraged to repair cases
|
|
of missing <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attributes, authors
|
|
must not rely on such behavior. <a href="#alt">Requirements for
|
|
providing text to act as an alternative for images</a> are described
|
|
in detail below.</p>
|
|
|
|
<p>The <em>contents</em> of <code><a href="#the-img-element">img</a></code> elements, if any, are
|
|
ignored for the purposes of rendering.</p>
|
|
|
|
</div><hr><p>The <code title="attr-hyperlink-usemap"><a href="the-map-element.html#attr-hyperlink-usemap">usemap</a></code> attribute,
|
|
if present, can indicate that the image has an associated
|
|
<a href="the-map-element.html#image-map">image map</a>.</p><p>The <dfn id="attr-img-ismap" title="attr-img-ismap"><code>ismap</code></dfn>
|
|
attribute, when used on an element that is a descendant of an
|
|
<code><a href="text-level-semantics.html#the-a-element">a</a></code> element with an <code title="attr-hyperlink-href"><a href="links.html#attr-hyperlink-href">href</a></code> attribute, indicates by its
|
|
presence that the element provides access to a server-side image
|
|
map. This affects how events are handled on the corresponding
|
|
<code><a href="text-level-semantics.html#the-a-element">a</a></code> element.</p><p>The <code title="attr-img-ismap"><a href="#attr-img-ismap">ismap</a></code> attribute is a
|
|
<a href="common-microsyntaxes.html#boolean-attribute">boolean attribute</a>. The attribute must not be specified
|
|
on an element that does not have an ancestor <code><a href="text-level-semantics.html#the-a-element">a</a></code> element
|
|
with an <code title="attr-hyperlink-href"><a href="links.html#attr-hyperlink-href">href</a></code> attribute.</p><p>The <code><a href="#the-img-element">img</a></code> element supports <a href="the-map-element.html#dimension-attributes">dimension
|
|
attributes</a>.</p><div class="impl">
|
|
|
|
<p>The IDL attributes <dfn id="dom-img-alt" title="dom-img-alt"><code>alt</code></dfn>, <dfn id="dom-img-src" title="dom-img-src"><code>src</code></dfn>, <dfn id="dom-img-usemap" title="dom-img-useMap"><code>useMap</code></dfn>, and <dfn id="dom-img-ismap" title="dom-img-isMap"><code>isMap</code></dfn> each must
|
|
<a href="common-dom-interfaces.html#reflect">reflect</a> the respective content attributes of the same
|
|
name.</p>
|
|
|
|
</div><dl class="domintro"><dt><var title="">image</var> . <code title="dom-img-width"><a href="#dom-img-width">width</a></code> [ = <var title="">value</var> ]</dt>
|
|
<dt><var title="">image</var> . <code title="dom-img-height"><a href="#dom-img-height">height</a></code> [ = <var title="">value</var> ]</dt>
|
|
|
|
<dd>
|
|
|
|
<p>These attributes return the actual rendered dimensions of the
|
|
image, or zero if the dimensions are not known.</p>
|
|
|
|
<p>They can be set, to change the corresponding content
|
|
attributes.</p>
|
|
|
|
</dd>
|
|
|
|
<dt><var title="">image</var> . <code title="dom-img-naturalWidth"><a href="#dom-img-naturalwidth">naturalWidth</a></code></dt>
|
|
<dt><var title="">image</var> . <code title="dom-img-naturalHeight"><a href="#dom-img-naturalheight">naturalHeight</a></code></dt>
|
|
|
|
<dd>
|
|
|
|
<p>These attributes return the intrinsic dimensions of the image,
|
|
or zero if the dimensions are not known.</p>
|
|
|
|
</dd>
|
|
|
|
<dt><var title="">image</var> . <code title="dom-img-complete"><a href="#dom-img-complete">complete</a></code></dt>
|
|
|
|
<dd>
|
|
|
|
<p>Returns true if the image has been completely downloaded or if
|
|
no image is specified; otherwise, returns false.</p>
|
|
|
|
</dd>
|
|
|
|
<dt><var title="">image</var> = new <code title="dom-image"><a href="#dom-image">Image</a></code>( [ <var title="">width</var> [, <var title="">height</var> ] ] )</dt>
|
|
|
|
<dd>
|
|
|
|
<p>Returns a new <code><a href="#the-img-element">img</a></code> element, with the <code title="attr-dim-width"><a href="the-map-element.html#attr-dim-width">width</a></code> and <code title="attr-dim-height"><a href="the-map-element.html#attr-dim-height">height</a></code> attributes set to the values
|
|
passed in the relevant arguments, if applicable.</p>
|
|
|
|
</dd>
|
|
|
|
</dl><div class="impl">
|
|
|
|
<p>The IDL attributes <dfn id="dom-img-width" title="dom-img-width"><code>width</code></dfn> and <dfn id="dom-img-height" title="dom-img-height"><code>height</code></dfn> must return the
|
|
rendered width and height of the image, in CSS pixels, if the image
|
|
is <a href="rendering.html#being-rendered">being rendered</a>, and is being rendered to a visual
|
|
medium; or else the intrinsic width and height of the image, in CSS
|
|
pixels, if the image is <i title="img-available">available</i> but
|
|
not being rendered to a visual medium; or else 0, if the image is
|
|
not <i title="img-available">available</i>. <a href="references.html#refsCSS">[CSS]</a></p>
|
|
|
|
<p>On setting, they must act as if they <a href="common-dom-interfaces.html#reflect" title="reflect">reflected</a> the respective content attributes
|
|
of the same name.</p>
|
|
|
|
<p>The IDL attributes <dfn id="dom-img-naturalwidth" title="dom-img-naturalWidth"><code>naturalWidth</code></dfn> and
|
|
<dfn id="dom-img-naturalheight" title="dom-img-naturalHeight"><code>naturalHeight</code></dfn>
|
|
must return the intrinsic width and height of the image, in CSS
|
|
pixels, if the image is <i title="img-available">available</i>, or
|
|
else 0. <a href="references.html#refsCSS">[CSS]</a></p>
|
|
|
|
<p>The IDL attribute <dfn id="dom-img-complete" title="dom-img-complete"><code>complete</code></dfn> must return
|
|
true if any of the following conditions is true:</p>
|
|
<ul class="brief"><li>The <code title="attr-img-src"><a href="#attr-img-src">src</a></code> attribute is omitted.
|
|
</li><li>The <code title="attr-img-src"><a href="#attr-img-src">src</a></code> attribute's value is the empty string.
|
|
</li><li>The final <a href="webappapis.html#concept-task" title="concept-task">task</a> that is <a href="webappapis.html#queue-a-task" title="queue a task">queued</a> by the <a href="webappapis.html#networking-task-source">networking task source</a> once the resource has been <a href="fetching-resources.html#fetch" title="fetch">fetched</a> has been <a href="webappapis.html#queue-a-task" title="queue a task">queued</a>, but has not yet been run, and the <code><a href="#the-img-element">img</a></code> element is not in the <a href="#img-error" title="img-error">broken</a> state.
|
|
</li><li>The <code><a href="#the-img-element">img</a></code> element is <a href="#img-all" title="img-all">completely available</a>.
|
|
</li></ul><p>Otherwise, the attribute must return false.</p>
|
|
|
|
<p class="note">The value of <code title="dom-img-complete"><a href="#dom-img-complete">complete</a></code> can thus change while a
|
|
<a href="webappapis.html#concept-script" title="concept-script">script</a> is executing.</p>
|
|
|
|
<p>Three constructors are provided for creating
|
|
<code><a href="#htmlimageelement">HTMLImageElement</a></code> objects (in addition to the factory
|
|
methods from DOM Core such as <code title="">createElement()</code>): <dfn id="dom-image" title="dom-image"><code>Image()</code></dfn>, <dfn id="dom-image-w" title="dom-image-w"><code>Image(<var title="">width</var>)</code></dfn>, and <dfn id="dom-image-wh" title="dom-image-wh"><code>Image(<var title="">width</var>, <var title="">height</var>)</code></dfn>. When invoked as constructors,
|
|
these must return a new <code><a href="#htmlimageelement">HTMLImageElement</a></code> object (a new
|
|
<code><a href="#the-img-element">img</a></code> element). If the <var title="">width</var> argument
|
|
is present, the new object's <code title="attr-dim-width"><a href="the-map-element.html#attr-dim-width">width</a></code> content attribute must be set to
|
|
<var title="">width</var>. If the <var title="">height</var>
|
|
argument is also present, the new object's <code title="attr-dim-height"><a href="the-map-element.html#attr-dim-height">height</a></code> content attribute must be set
|
|
to <var title="">height</var>. The element's document must be the
|
|
<a href="browsers.html#active-document">active document</a> of the <a href="browsers.html#browsing-context">browsing context</a> of
|
|
the <code><a href="browsers.html#window">Window</a></code> object on which the interface object of the
|
|
invoked constructor is found.</p>
|
|
|
|
</div><div class="example">
|
|
|
|
<p>A single image can have different appropriate alternative text
|
|
depending on the context.</p>
|
|
|
|
<p>In each of the following cases, the same image is used, yet the
|
|
<code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> text is different each
|
|
time. The image is the coat of arms of the Carouge municipality in
|
|
the canton Geneva in Switzerland.</p>
|
|
|
|
<p>Here it is used as a supplementary icon:</p>
|
|
<pre><p>I lived in <img src="carouge.svg" alt=""> Carouge.</p></pre>
|
|
|
|
<p>Here it is used as an icon representing the town:</p>
|
|
<pre><p>Home town: <img src="carouge.svg" alt="Carouge"></p></pre>
|
|
|
|
<p>Here it is used as part of a text on the town:</p>
|
|
|
|
<pre><p>Carouge has a coat of arms.</p>
|
|
<p><img src="carouge.svg" alt="The coat of arms depicts a lion, sitting in front of a tree."></p>
|
|
<p>It is used as decoration all over the town.</p></pre>
|
|
|
|
<p>Here it is used as a way to support a similar text where the
|
|
description is given as well as, instead of as an alternative to,
|
|
the image:</p>
|
|
|
|
<pre><p>Carouge has a coat of arms.</p>
|
|
<p><img src="carouge.svg" alt=""></p>
|
|
<p>The coat of arms depicts a lion, sitting in front of a tree.
|
|
It is used as decoration all over the town.</p></pre>
|
|
|
|
<p>Here it is used as part of a story:</p>
|
|
|
|
<pre><p>He picked up the folder and a piece of paper fell out.</p>
|
|
<p><img src="carouge.svg" alt="Shaped like a shield, the paper had a
|
|
red background, a green tree, and a yellow lion with its tongue
|
|
hanging out and whose tail was shaped like an S."></p>
|
|
<p>He stared at the folder. S! The answer he had been looking for all
|
|
this time was simply the letter S! How had he not seen that before? It all
|
|
came together now. The phone call where Hector had referred to a lion's tail,
|
|
the time Marco had stuck his tongue out...</p></pre>
|
|
|
|
<p>Here it is not known at the time of publication what the image
|
|
will be, only that it will be a coat of arms of some kind, and thus
|
|
no replacement text can be provided, and instead only a brief
|
|
caption for the image is provided, in the <code title="attr-title"><a href="elements.html#the-title-attribute">title</a></code> attribute:</p>
|
|
|
|
<pre><p>The last user to have uploaded a coat of arms uploaded this one:</p>
|
|
<p><img src="last-uploaded-coat-of-arms.cgi" title="User-uploaded coat of arms."></p></pre>
|
|
|
|
<p>Ideally, the author would find a way to provide real replacement
|
|
text even in this case, e.g. by asking the previous user. Not
|
|
providing replacement text makes the document more difficult to use
|
|
for people who are unable to view images, e.g. blind users, or
|
|
users or very low-bandwidth connections or who pay by the byte, or
|
|
users who are forced to use a text-only Web browser.</p>
|
|
|
|
</div><div class="example">
|
|
|
|
<p>Here are some more examples showing the same picture used in
|
|
different contexts, with different appropriate alternate texts each
|
|
time.</p>
|
|
|
|
<pre><article>
|
|
<h1>My cats</h1>
|
|
<h2>Fluffy</h2>
|
|
<p>Fluffy is my favorite.</p>
|
|
<img src="fluffy.jpg" alt="She likes playing with a ball of yarn.">
|
|
<p>She's just too cute.</p>
|
|
<h2>Miles</h2>
|
|
<p>My other cat, Miles just eats and sleeps.</p>
|
|
</article></pre>
|
|
|
|
<pre><article>
|
|
<h1>Photography</h1>
|
|
<h2>Shooting moving targets indoors</h2>
|
|
<p>The trick here is to know how to anticipate; to know at what speed and
|
|
what distance the subject will pass by.</p>
|
|
<img src="fluffy.jpg" alt="A cat flying by, chasing a ball of yarn, can be
|
|
photographed quite nicely using this technique.">
|
|
<h2>Nature by night</h2>
|
|
<p>To achieve this, you'll need either an extremely sensitive film, or
|
|
immense flash lights.</p>
|
|
</article></pre>
|
|
|
|
<pre><article>
|
|
<h1>About me</h1>
|
|
<h2>My pets</h2>
|
|
<p>I've got a cat named Fluffy and a dog named Miles.</p>
|
|
<img src="fluffy.jpg" alt="Fluffy, my cat, tends to keep itself busy.">
|
|
<p>My dog Miles and I like go on long walks together.</p>
|
|
<h2>music</h2>
|
|
<p>After our walks, having emptied my mind, I like listening to Bach.</p>
|
|
</article></pre>
|
|
|
|
<pre><article>
|
|
<h1>Fluffy and the Yarn</h1>
|
|
<p>Fluffy was a cat who liked to play with yarn. He also liked to jump.</p>
|
|
<aside><img src="fluffy.jpg" alt="" title="Fluffy"></aside>
|
|
<p>He would play in the morning, he would play in the evening.</p>
|
|
</article></pre>
|
|
|
|
</div><h5 id="alt"><span class="secno">4.8.1.1 </span>Requirements for providing text to act as an alternative for images</h5><h6 id="general-guidelines"><span class="secno">4.8.1.1.1 </span>General guidelines</h6><p>Except where otherwise specified, the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute must be specified and its
|
|
value must not be empty; the value must be an appropriate
|
|
replacement for the image. The specific requirements for the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute depend on what the image
|
|
is intended to represent, as described in the following
|
|
sections.</p><p>The most general rule to consider when writing alternative text
|
|
is the following: <strong>the intent is that replacing every image
|
|
with the text of its <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute
|
|
not change the meaning of the page</strong>.</p><p>So, in general, alternative text can be written by considering
|
|
what one would have written had one not been able to include the
|
|
image.</p><p>A corollary to this is that the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute's value should never
|
|
contain text that could be considered the image's <em>caption</em>,
|
|
<em>title</em>, or <em>legend</em>. It is supposed to contain
|
|
replacement text that could be used by users <em>instead</em> of the
|
|
image; it is not meant to supplement the image. The <code title="attr-title"><a href="elements.html#the-title-attribute">title</a></code> attribute can be used for
|
|
supplemental information.</p><p class="note">One way to think of alternative text is to think
|
|
about how you would read the page containing the image to someone
|
|
over the phone, without mentioning that there is an image
|
|
present. Whatever you say instead of the image is typically a good
|
|
start for writing the alternative text.</p><h6 id="a-link-or-button-containing-nothing-but-the-image"><span class="secno">4.8.1.1.2 </span>A link or button containing nothing but the image</h6><p>When an <a href="text-level-semantics.html#the-a-element">a</a> element that creates a
|
|
<a href="links.html#hyperlink">hyperlink</a>, or a <code><a href="the-button-element.html#the-button-element">button</a></code> element, has no
|
|
textual content but contains one or more images, the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attributes must contain text that
|
|
together convey the purpose of the link or button.</p><div class="example">
|
|
|
|
<p>In this example, a user is asked to pick his preferred color
|
|
from a list of three. Each color is given by an image, but for
|
|
users who have configured their user agent not to display images,
|
|
the color names are used instead:</p>
|
|
|
|
<pre><h1>Pick your color</h1>
|
|
<ul>
|
|
<li><a href="green.html"><strong><img src="green.jpeg" alt="Green"></strong></a></li>
|
|
<li><a href="blue.html"><strong><img src="blue.jpeg" alt="Blue"></strong></a></li>
|
|
<li><a href="red.html"><strong><img src="red.jpeg" alt="Red"></strong></a></li>
|
|
</ul></pre>
|
|
|
|
</div><div class="example">
|
|
|
|
<p>In this example, each button has a set of images to indicate the
|
|
kind of color output desired by the user. The first image is used
|
|
in each case to give the alternative text.</p>
|
|
|
|
<pre><button name="rgb"><strong><img src="red" alt="RGB"><img src="green" alt=""><img src="blue" alt=""></strong></button>
|
|
<button name="cmyk"><strong><img src="cyan" alt="CMYK"><img src="magenta" alt=""><img src="yellow" alt=""><img src="black" alt=""></strong></button></pre>
|
|
|
|
<p>Since each image represents one part of the text, it could also
|
|
be written like this:</p>
|
|
|
|
<pre><button name="rgb"><strong><img src="red" alt="R"><img src="green" alt="G"><img src="blue" alt="B"></strong></button>
|
|
<button name="cmyk"><strong><img src="cyan" alt="C"><img src="magenta" alt="M"><img src="yellow" alt="Y"><img src="black" alt="K"></strong></button></pre>
|
|
|
|
<p>However, with other alternative text, this might not work, and
|
|
putting all the alternative text into one image in each case might
|
|
make more sense:</p>
|
|
|
|
<pre><button name="rgb"><strong><img src="red" alt="sRGB profile"><img src="green" alt=""><img src="blue" alt=""></strong></button>
|
|
<button name="cmyk"><strong><img src="cyan" alt="CMYK profile"><img src="magenta" alt=""><img src="yellow" alt=""><img src="black" alt=""></strong></button></pre>
|
|
|
|
</div><h6 id="a-phrase-or-paragraph-with-an-alternative-graphical-representation:-charts-diagrams-graphs-maps-illustrations"><span class="secno">4.8.1.1.3 </span>A phrase or paragraph with an alternative graphical representation: charts, diagrams, graphs, maps, illustrations</h6><p>Sometimes something can be more clearly stated in graphical
|
|
form, for example as a flowchart, a diagram, a graph, or a simple
|
|
map showing directions. In such cases, an image can be given using
|
|
the <code><a href="#the-img-element">img</a></code> element, but the lesser textual version must
|
|
still be given, so that users who are unable to view the image
|
|
(e.g. because they have a very slow connection, or because they
|
|
are using a text-only browser, or because they are listening to
|
|
the page being read out by a hands-free automobile voice Web
|
|
browser, or simply because they are blind) are still able to
|
|
understand the message being conveyed.</p><p>The text must be given in the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute, and must convey the
|
|
same message as the image specified in the <code title="attr-img-src"><a href="#attr-img-src">src</a></code> attribute.</p><p>It is important to realize that the alternative text is a
|
|
<em>replacement</em> for the image, not a description of the
|
|
image.</p><div class="example">
|
|
|
|
<p>In the following example we have <a href="images/parsing-model-overview.png">a flowchart</a> in image
|
|
form, with text in the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code>
|
|
attribute rephrasing the flowchart in prose form:</p>
|
|
|
|
<pre><p>In the common case, the data handled by the tokenization stage
|
|
comes from the network, but it can also come from script.</p>
|
|
<p><strong><img src="parsing-model-overview.png" alt="The network
|
|
passes data to the Tokenizer stage, which passes data to the Tree
|
|
Construction stage. From there, data goes to both the DOM and to
|
|
Script Execution. Script Execution is linked to the DOM, and, using
|
|
document.write(), passes data to the Tokenizer."></strong></p></pre>
|
|
|
|
</div><div class="example">
|
|
|
|
<p>Here's another example, showing a good solution and a bad
|
|
solution to the problem of including an image in a
|
|
description.</p>
|
|
|
|
<p>First, here's the good solution. This sample shows how the
|
|
alternative text should just be what you would have put in the
|
|
prose if the image had never existed.</p>
|
|
|
|
<pre><!-- This is the correct way to do things. -->
|
|
<p>
|
|
You are standing in an open field west of a house.
|
|
<strong><img src="house.jpeg" alt="The house is white, with a boarded front door."></strong>
|
|
There is a small mailbox here.
|
|
</p></pre>
|
|
|
|
<p>Second, here's the bad solution. In this incorrect way of
|
|
doing things, the alternative text is simply a description of the
|
|
image, instead of a textual replacement for the image. It's bad
|
|
because when the image isn't shown, the text doesn't flow as well
|
|
as in the first example.</p>
|
|
|
|
<pre class="bad"><!-- <em>This is the wrong way to do things.</em> -->
|
|
<p>
|
|
You are standing in an open field west of a house.
|
|
<img src="house.jpeg" alt="A white house, with a boarded front door.">
|
|
There is a small mailbox here.
|
|
</p></pre>
|
|
|
|
<p>Text such as "Photo of white house with boarded door" would be
|
|
equally bad alternative text (though it could be suitable for the
|
|
<code title="attr-title"><a href="elements.html#the-title-attribute">title</a></code> attribute or in the
|
|
<code><a href="grouping-content.html#the-figcaption-element">figcaption</a></code> element of a <code><a href="grouping-content.html#the-figure-element">figure</a></code> with this
|
|
image).</p>
|
|
|
|
</div><h6 id="a-short-phrase-or-label-with-an-alternative-graphical-representation:-icons-logos"><span class="secno">4.8.1.1.4 </span>A short phrase or label with an alternative graphical representation: icons, logos</h6><p>A document can contain information in iconic form. The icon is
|
|
intended to help users of visual browsers to recognize features at
|
|
a glance.</p><p>In some cases, the icon is supplemental to a text label
|
|
conveying the same meaning. In those cases, the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute must be present but must
|
|
be empty.</p><div class="example">
|
|
|
|
<p>Here the icons are next to text that conveys the same meaning,
|
|
so they have an empty <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code>
|
|
attribute:</p>
|
|
|
|
<pre><nav>
|
|
<p><a href="/help/"><strong><img src="/icons/help.png" alt=""></strong> Help</a></p>
|
|
<p><a href="/configure/"><strong><img src="/icons/configuration.png" alt=""></strong>
|
|
Configuration Tools</a></p>
|
|
</nav></pre>
|
|
|
|
</div><p>In other cases, the icon has no text next to it describing what
|
|
it means; the icon is supposed to be self-explanatory. In those
|
|
cases, an equivalent textual label must be given in the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute.</p><div class="example">
|
|
|
|
<p>Here, posts on a news site are labeled with an icon
|
|
indicating their topic.</p>
|
|
|
|
<pre><body>
|
|
<article>
|
|
<header>
|
|
<h1>Ratatouille wins <i>Best Movie of the Year</i> award</h1>
|
|
<p><strong><img src="movies.png" alt="Movies"></strong></p>
|
|
</header>
|
|
<p>Pixar has won yet another <i>Best Movie of the Year</i> award,
|
|
making this its 8th win in the last 12 years.</p>
|
|
</article>
|
|
<article>
|
|
<header>
|
|
<h1>Latest TWiT episode is online</h1>
|
|
<p><strong><img src="podcasts.png" alt="Podcasts"></strong></p>
|
|
</header>
|
|
<p>The latest TWiT episode has been posted, in which we hear
|
|
several tech news stories as well as learning much more about the
|
|
iPhone. This week, the panelists compare how reflective their
|
|
iPhones' Apple logos are.</p>
|
|
</article>
|
|
</body></pre>
|
|
|
|
</div><p>Many pages include logos, insignia, flags, or emblems, which
|
|
stand for a particular entity such as a company, organization,
|
|
project, band, software package, country, or some such.</p><p>If the logo is being used to represent the entity, e.g. as a page
|
|
heading, the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute must
|
|
contain the name of the entity being represented by the logo. The
|
|
<code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute must <em>not</em>
|
|
contain text like the word "logo", as it is not the fact that it is
|
|
a logo that is being conveyed, it's the entity itself.</p><p>If the logo is being used next to the name of the entity that
|
|
it represents, then the logo is supplemental, and its <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute must instead be
|
|
empty.</p><p>If the logo is merely used as decorative material (as branding,
|
|
or, for example, as a side image in an article that mentions the
|
|
entity to which the logo belongs), then the entry below on purely
|
|
decorative images applies. If the logo is actually being
|
|
discussed, then it is being used as a phrase or paragraph (the
|
|
description of the logo) with an alternative graphical
|
|
representation (the logo itself), and the first entry above
|
|
applies.</p><div class="example">
|
|
|
|
<p>In the following snippets, all four of the above cases are
|
|
present. First, we see a logo used to represent a company:</p>
|
|
|
|
<pre><h1><strong><img src="XYZ.gif" alt="The XYZ company"></strong></h1></pre>
|
|
|
|
<p>Next, we see a paragraph which uses a logo right next to the
|
|
company name, and so doesn't have any alternative text:
|
|
|
|
</p><pre><article>
|
|
<h2>News</h2>
|
|
<p>We have recently been looking at buying the <strong><img src="alpha.gif"
|
|
alt=""> ΑΒΓ company</strong>, a small Greek company
|
|
specializing in our type of product.</p></pre>
|
|
|
|
<p>In this third snippet, we have a logo being used in an aside,
|
|
as part of the larger article discussing the acquisition:</p>
|
|
|
|
<pre> <strong><aside><p><img src="alpha-large.gif" alt=""></p></aside></strong>
|
|
<p>The ΑΒΓ company has had a good quarter, and our
|
|
pie chart studies of their accounts suggest a much bigger blue slice
|
|
than its green and orange slices, which is always a good sign.</p>
|
|
</article></pre>
|
|
|
|
<p>Finally, we have an opinion piece talking about a logo, and
|
|
the logo is therefore described in detail in the alternative
|
|
text.</p>
|
|
|
|
<pre><p>Consider for a moment their logo:</p>
|
|
|
|
<strong><p><img src="/images/logo" alt="It consists of a green circle with a
|
|
green question mark centered inside it."></p></strong>
|
|
|
|
<p>How unoriginal can you get? I mean, oooooh, a question mark, how
|
|
<em>revolutionary</em>, how utterly <em>ground-breaking</em>, I'm
|
|
sure everyone will rush to adopt those specifications now! They could
|
|
at least have tried for some sort of, I don't know, sequence of
|
|
rounded squares with varying shades of green and bold white outlines,
|
|
at least that would look good on the cover of a blue book.</p></pre>
|
|
|
|
<p>This example shows how the alternative text should be written
|
|
such that if the image isn't <i title="img-available">available</i>, and the text is used instead,
|
|
the text flows seamlessly into the surrounding text, as if the
|
|
image had never been there in the first place.</p>
|
|
|
|
</div><h6 id="text-that-has-been-rendered-to-a-graphic-for-typographical-effect"><span class="secno">4.8.1.1.5 </span>Text that has been rendered to a graphic for typographical effect</h6><p>Sometimes, an image just consists of text, and the purpose of the
|
|
image is not to highlight the actual typographic effects used to
|
|
render the text, but just to convey the text itself.</p><p>In such cases, the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code>
|
|
attribute must be present but must consist of the same text as
|
|
written in the image itself.</p><div class="example">
|
|
|
|
<p>Consider a graphic containing the text "Earth Day", but with the
|
|
letters all decorated with flowers and plants. If the text is
|
|
merely being used as a heading, to spice up the page for graphical
|
|
users, then the correct alternative text is just the same text
|
|
"Earth Day", and no mention need be made of the decorations:</p>
|
|
|
|
<pre><h1><strong><img src="earthdayheading.png" alt="Earth Day"></strong></h1></pre>
|
|
|
|
</div><h6 id="a-graphical-representation-of-some-of-the-surrounding-text"><span class="secno">4.8.1.1.6 </span>A graphical representation of some of the surrounding text</h6><p>In many cases, the image is actually just supplementary, and
|
|
its presence merely reinforces the surrounding text. In these
|
|
cases, the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute must be
|
|
present but its value must be the empty string.</p><p>In general, an image falls into this category if removing the
|
|
image doesn't make the page any less useful, but including the
|
|
image makes it a lot easier for users of visual browsers to
|
|
understand the concept.</p><div class="example">
|
|
|
|
<p>A flowchart that repeats the previous paragraph in graphical form:</p>
|
|
|
|
<pre><p>The network passes data to the Tokenizer stage, which
|
|
passes data to the Tree Construction stage. From there, data goes
|
|
to both the DOM and to Script Execution. Script Execution is
|
|
linked to the DOM, and, using document.write(), passes data to
|
|
the Tokenizer.</p>
|
|
<strong><p><img src="parsing-model-overview.png" alt=""></p></strong></pre>
|
|
|
|
<p>In these cases, it would be wrong to include alternative text
|
|
that consists of just a caption. If a caption is to be included,
|
|
then either the <code title="attr-title"><a href="elements.html#the-title-attribute">title</a></code> attribute can
|
|
be used, or the <code><a href="grouping-content.html#the-figure-element">figure</a></code> and <code><a href="grouping-content.html#the-figcaption-element">figcaption</a></code>
|
|
elements can be used. In the latter case, the image would in fact
|
|
be a phrase or paragraph with an alternative graphical
|
|
representation, and would thus require alternative text.</p>
|
|
|
|
<pre><!-- Using the title="" attribute -->
|
|
<p>The network passes data to the Tokenizer stage, which
|
|
passes data to the Tree Construction stage. From there, data goes
|
|
to both the DOM and to Script Execution. Script Execution is
|
|
linked to the DOM, and, using document.write(), passes data to
|
|
the Tokenizer.</p>
|
|
<p><strong><img src="parsing-model-overview.png" alt=""
|
|
title="Flowchart representation of the parsing model."></strong></p></pre>
|
|
|
|
<pre><!-- Using <figure> and <figcaption> -->
|
|
<p>The network passes data to the Tokenizer stage, which
|
|
passes data to the Tree Construction stage. From there, data goes
|
|
to both the DOM and to Script Execution. Script Execution is
|
|
linked to the DOM, and, using document.write(), passes data to
|
|
the Tokenizer.</p>
|
|
<figure>
|
|
<strong><img src="parsing-model-overview.png" alt="The Network leads
|
|
to the Tokenizer, which leads to the Tree Construction. The Tree
|
|
Construction leads to two items. The first is Script Execution, which
|
|
leads via document.write() back to the Tokenizer. The second item
|
|
from which Tree Construction leads is the DOM. The DOM is related to
|
|
the Script Execution."></strong>
|
|
<figcaption>Flowchart representation of the parsing model.</figcaption>
|
|
</figure></pre>
|
|
|
|
<pre class="bad"><!-- This is WRONG. Do not do this. Instead, do what the above examples do. -->
|
|
<p>The network passes data to the Tokenizer stage, which
|
|
passes data to the Tree Construction stage. From there, data goes
|
|
to both the DOM and to Script Execution. Script Execution is
|
|
linked to the DOM, and, using document.write(), passes data to
|
|
the Tokenizer.</p>
|
|
<p><img src="parsing-model-overview.png"
|
|
alt="Flowchart representation of the parsing model."></p>
|
|
<!-- Never put the image's caption in the alt="" attribute! --></pre>
|
|
|
|
</div><div class="example">
|
|
|
|
<p>A graph that repeats the previous paragraph in graphical form:</p>
|
|
|
|
<pre><p>According to a study covering several billion pages,
|
|
about 62% of documents on the Web in 2007 triggered the Quirks
|
|
rendering mode of Web browsers, about 30% triggered the Almost
|
|
Standards mode, and about 9% triggered the Standards mode.</p>
|
|
<strong><p><img src="rendering-mode-pie-chart.png" alt=""></p></strong></pre>
|
|
|
|
</div><h6 id="a-purely-decorative-image-that-doesn-t-add-any-information"><span class="secno">4.8.1.1.7 </span>A purely decorative image that doesn't add any information</h6><p>If an image is decorative but isn't especially page-specific
|
|
— for example an image that forms part of a site-wide design
|
|
scheme — the image should be specified in the site's CSS, not
|
|
in the markup of the document.</p><p>Exceptions to this rule, in cases where CSS cannot be used to
|
|
display an entirely decorative image, are covered by the HTML5:
|
|
Techniques for providing useful text alternatives. <a href="references.html#refsHTMLALTTECHS">[HTMLALTTECHS]</a>
|
|
Authors are also encouraged to consult the Web Content Accessibility
|
|
Guidelines 2.0 for more detailed information and acceptable
|
|
techniques. <a href="references.html#refsWCAG">[WCAG]</a></p><h6 id="a-group-of-images-that-form-a-single-larger-picture-with-no-links"><span class="secno">4.8.1.1.8 </span>A group of images that form a single larger picture with no links</h6><p>When a picture has been sliced into smaller image files that are
|
|
then displayed together to form the complete picture again, one of
|
|
the images must have its <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code>
|
|
attribute set as per the relevant rules that would be appropriate
|
|
for the picture as a whole, and then all the remaining images must
|
|
have their <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute set to
|
|
the empty string.</p><div class="example">
|
|
|
|
<p>In the following example, a picture representing a company logo
|
|
for <span title="">XYZ Corp</span> has been split into two pieces,
|
|
the first containing the letters "XYZ" and the second with the word
|
|
"Corp". The alternative text ("XYZ Corp") is all in the first
|
|
image.</p>
|
|
|
|
<pre><h1><strong><img src="logo1.png" alt="XYZ Corp"><img src="logo2.png" alt=""></strong></h1></pre>
|
|
|
|
</div><div class="example">
|
|
|
|
<p>In the following example, a rating is shown as three filled
|
|
stars and two empty stars. While the alternative text could have
|
|
been "★★★☆☆", the author has
|
|
instead decided to more helpfully give the rating in the form "3
|
|
out of 5". That is the alternative text of the first image, and the
|
|
rest have blank alternative text.</p>
|
|
|
|
<pre><p>Rating: <meter max=5 value=3><strong><img src="1" alt="3 out of 5"
|
|
><img src="1" alt=""><img src="1" alt=""><img src="0" alt=""
|
|
><img src="0" alt=""></strong></meter></p></pre>
|
|
|
|
</div><h6 id="a-group-of-images-that-form-a-single-larger-picture-with-links"><span class="secno">4.8.1.1.9 </span>A group of images that form a single larger picture with links</h6><p>Generally, <a href="the-map-element.html#image-map" title="image map">image maps</a> should be
|
|
used instead of slicing an image for links.</p><p>However, if an image is indeed sliced and any of the components
|
|
of the sliced picture are the sole contents of links, then one image
|
|
per link must have alternative text in its <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute representing the purpose
|
|
of the link.</p><div class="example">
|
|
|
|
<p>In the following example, a picture representing the flying
|
|
spaghetti monster emblem, with each of the left noodly appendages
|
|
and the right noodly appendages in different images, so that the
|
|
user can pick the left side or the right side in an adventure.</p>
|
|
|
|
<pre><h1>The Church</h1>
|
|
<p>You come across a flying spaghetti monster. Which side of His
|
|
Noodliness do you wish to reach out for?</p>
|
|
<strong><p><a href="?go=left" ><img src="fsm-left.png" alt="Left side. "></a
|
|
><img src="fsm-middle.png" alt=""
|
|
><a href="?go=right"><img src="fsm-right.png" alt="Right side."></a></p></strong></pre>
|
|
|
|
</div><h6 id="a-key-part-of-the-content"><span class="secno">4.8.1.1.10 </span>A key part of the content</h6><p>In some cases, the image is a critical part of the
|
|
content. This could be the case, for instance, on a page that is
|
|
part of a photo gallery. The image is the whole <em>point</em> of
|
|
the page containing it.</p><p>How to provide alternative text for an image that is a key part
|
|
of the content depends on the image's provenance.</p><dl><dt>The general case</dt>
|
|
|
|
<dd>
|
|
|
|
<p>When it is possible for detailed alternative text to be
|
|
provided, for example if the image is part of a series of
|
|
screenshots in a magazine review, or part of a comic strip, or is
|
|
a photograph in a blog entry about that photograph, text that can
|
|
serve as a substitute for the image must be given as the contents
|
|
of the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute.</p>
|
|
|
|
<div class="example">
|
|
|
|
<p>A screenshot in a gallery of screenshots for a new OS, with
|
|
some alternative text:</p>
|
|
|
|
<pre><figure>
|
|
<strong><img src="KDE%20Light%20desktop.png"
|
|
alt="The desktop is blue, with icons along the left hand side in
|
|
two columns, reading System, Home, K-Mail, etc. A window is
|
|
open showing that menus wrap to a second line if they
|
|
cannot fit in the window. The window has a list of icons
|
|
along the top, with an address bar below it, a list of
|
|
icons for tabs along the left edge, a status bar on the
|
|
bottom, and two panes in the middle. The desktop has a bar
|
|
at the bottom of the screen with a few buttons, a pager, a
|
|
list of open applications, and a clock."></strong>
|
|
<figcaption>Screenshot of a KDE desktop.</figcaption>
|
|
</figure></pre>
|
|
|
|
</div>
|
|
|
|
<div class="example">
|
|
|
|
<p>A graph in a financial report:</p>
|
|
|
|
<pre><strong><img src="sales.gif"
|
|
title="Sales graph"
|
|
alt="From 1998 to 2005, sales increased by the following percentages
|
|
with each year: 624%, 75%, 138%, 40%, 35%, 9%, 21%"></strong></pre>
|
|
|
|
<p>Note that "sales graph" would be inadequate alternative text
|
|
for a sales graph. Text that would be a good <em>caption</em> is
|
|
not generally suitable as replacement text.</p>
|
|
|
|
</div>
|
|
|
|
</dd>
|
|
|
|
|
|
<dt>Images that defy a complete description</dt>
|
|
|
|
<dd>
|
|
|
|
<p>In certain cases, the nature of the image might be such that
|
|
providing thorough alternative text is impractical. For example,
|
|
the image could be indistinct, or could be a complex fractal, or
|
|
could be a detailed topographical map.</p>
|
|
|
|
<p>In these cases, the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code>
|
|
attribute must contain some suitable alternative text, but it may
|
|
be somewhat brief.</p>
|
|
|
|
<div class="example">
|
|
|
|
<p>Sometimes there simply is no text that can do justice to an
|
|
image. For example, there is little that can be said to usefully
|
|
describe a Rorschach inkblot test. However, a description, even
|
|
if brief, is still better than nothing:</p>
|
|
|
|
<pre><figure>
|
|
<strong><img src="/commons/a/a7/Rorschach1.jpg" alt="A shape with left-right
|
|
symmetry with indistinct edges, with a small gap in the center, two
|
|
larger gaps offset slightly from the center, with two similar gaps
|
|
under them. The outline is wider in the top half than the bottom
|
|
half, with the sides extending upwards higher than the center, and
|
|
the center extending below the sides."></strong>
|
|
<figcaption>A black outline of the first of the ten cards
|
|
in the Rorschach inkblot test.</figcaption>
|
|
</figure></pre>
|
|
|
|
<p>Note that the following would be a very bad use of alternative
|
|
text:</p>
|
|
|
|
<pre class="bad"><!-- This example is wrong. Do not copy it. -->
|
|
<figure>
|
|
<img src="/commons/a/a7/Rorschach1.jpg" alt="A black outline
|
|
of the first of the ten cards in the Rorschach inkblot test.">
|
|
<figcaption>A black outline of the first of the ten cards
|
|
in the Rorschach inkblot test.</figcaption>
|
|
</figure></pre>
|
|
|
|
<p>Including the caption in the alternative text like this isn't
|
|
useful because it effectively duplicates the caption for users
|
|
who don't have images, taunting them twice yet not helping them
|
|
any more than if they had only read or heard the caption
|
|
once.</p>
|
|
|
|
</div>
|
|
|
|
<div class="example">
|
|
|
|
<p>Another example of an image that defies full description is a
|
|
fractal, which, by definition, is infinite in detail.</p>
|
|
|
|
<p>The following example shows one possible way of providing
|
|
alternative text for the full view of an image of the Mandelbrot
|
|
set.</p>
|
|
|
|
<pre><strong><img src="ms1.jpeg" alt="The Mandelbrot set appears as a cardioid with
|
|
its cusp on the real axis in the positive direction, with a smaller
|
|
bulb aligned along the same center line, touching it in the negative
|
|
direction, and with these two shapes being surrounded by smaller bulbs
|
|
of various sizes."></strong></pre>
|
|
|
|
</div>
|
|
|
|
</dd>
|
|
|
|
|
|
<dt id="unknown-images">Images whose contents are not known</dt>
|
|
|
|
<dd>
|
|
|
|
<p>In some unfortunate cases, there might be no alternative text
|
|
available at all, either because the image is obtained in some
|
|
automated fashion without any associated alternative text (e.g. a
|
|
Webcam), or because the page is being generated by a script using
|
|
user-provided images where the user did not provide suitable or
|
|
usable alternative text (e.g. photograph sharing sites), or
|
|
because the author does not himself know what the images represent
|
|
(e.g. a blind photographer sharing an image on his blog).</p>
|
|
|
|
<p>In such cases, the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code>
|
|
attribute may be omitted, but one of the following conditions must
|
|
be met as well:</p>
|
|
|
|
<ul><li>The <code title="attr-title"><a href="elements.html#the-title-attribute">title</a></code> attribute is
|
|
present and has a non-empty value.</li>
|
|
|
|
<li id="figcaption-as-alt-condition">The <code><a href="#the-img-element">img</a></code> element
|
|
is in a <code><a href="grouping-content.html#the-figure-element">figure</a></code> element that contains a
|
|
<code><a href="grouping-content.html#the-figcaption-element">figcaption</a></code> element that contains content other than
|
|
<a href="content-models.html#inter-element-whitespace">inter-element whitespace</a>, and, ignoring the
|
|
<code><a href="grouping-content.html#the-figcaption-element">figcaption</a></code> element and its descendants, the
|
|
<code><a href="grouping-content.html#the-figure-element">figure</a></code> element has no text node descendants other
|
|
than <a href="content-models.html#inter-element-whitespace">inter-element whitespace</a>, and no <a href="content-models.html#embedded-content">embedded
|
|
content</a> descendant other than the <code><a href="#the-img-element">img</a></code>
|
|
element.</li>
|
|
|
|
</ul><p class="note">Such cases are to be kept to an absolute
|
|
minimum. If there is even the slightest possibility of the author
|
|
having the ability to provide real alternative text, then it would
|
|
not be acceptable to omit the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code>
|
|
attribute.</p>
|
|
|
|
<div class="example">
|
|
|
|
<p>A photo on a photo-sharing site, if the site received the
|
|
image with no metadata other than the caption, could be marked up
|
|
as follows:</p>
|
|
|
|
<pre><figure>
|
|
<strong><img src="1100670787_6a7c664aef.jpg"></strong>
|
|
<figcaption>Bubbles traveled everywhere with us.</figcaption>
|
|
</figure></pre>
|
|
|
|
<p>It would be better, however, if a detailed description of the
|
|
important parts of the image obtained from the user and included
|
|
on the page.</p>
|
|
|
|
</div>
|
|
|
|
<div class="example">
|
|
|
|
<p>A blind user's blog in which a photo taken by the user is
|
|
shown. Initially, the user might not have any idea what the photo
|
|
he took shows:</p>
|
|
|
|
<pre><article>
|
|
<h1>I took a photo</h1>
|
|
<p>I went out today and took a photo!</p>
|
|
<figure>
|
|
<strong><img src="photo2.jpeg"></strong>
|
|
<figcaption>A photograph taken blindly from my front porch.</figcaption>
|
|
</figure>
|
|
</article></pre>
|
|
|
|
<p>Eventually though, the user might obtain a description of the
|
|
image from his friends and could then include alternative text:</p>
|
|
|
|
<pre><article>
|
|
<h1>I took a photo</h1>
|
|
<p>I went out today and took a photo!</p>
|
|
<figure>
|
|
<strong><img src="photo2.jpeg" alt="The photograph shows my hummingbird
|
|
feeder hanging from the edge of my roof. It is half full, but there
|
|
are no birds around. In the background, out-of-focus trees fill the
|
|
shot. The feeder is made of wood with a metal grate, and it contains
|
|
peanuts. The edge of the roof is wooden too, and is painted white
|
|
with light blue streaks."></strong>
|
|
<figcaption>A photograph taken blindly from my front porch.</figcaption>
|
|
</figure>
|
|
</article></pre>
|
|
|
|
</div>
|
|
|
|
<div class="example">
|
|
|
|
<p>Sometimes the entire point of the image is that a textual
|
|
description is not available, and the user is to provide the
|
|
description. For instance, the point of a CAPTCHA image is to see
|
|
if the user can literally read the graphic. Here is one way to
|
|
mark up a CAPTCHA (note the <code title="attr-title"><a href="elements.html#the-title-attribute">title</a></code>
|
|
attribute):</p>
|
|
|
|
<pre><p><label>What does this image say?
|
|
<strong><img src="captcha.cgi?id=8934" title="CAPTCHA"></strong>
|
|
<input type=text name=captcha></label>
|
|
(If you cannot see the image, you can use an <a
|
|
href="?audio">audio</a> test instead.)</p></pre>
|
|
|
|
<p>Another example would be software that displays images and
|
|
asks for alternative text precisely for the purpose of then
|
|
writing a page with correct alternative text. Such a page could
|
|
have a table of images, like this:</p>
|
|
|
|
<pre><table>
|
|
<thead>
|
|
<tr> <th> Image <th> Description
|
|
<tbody>
|
|
<tr>
|
|
<td> <strong><img src="2421.png" title="Image 640 by 100, filename 'banner.gif'"></strong>
|
|
<td> <input name="alt2421">
|
|
<tr>
|
|
<td> <strong><img src="2422.png" title="Image 200 by 480, filename 'ad3.gif'"></strong>
|
|
<td> <input name="alt2422">
|
|
</table></pre>
|
|
|
|
<p>Notice that even in this example, as much useful information
|
|
as possible is still included in the <code title="attr-title"><a href="elements.html#the-title-attribute">title</a></code> attribute.</p>
|
|
|
|
</div>
|
|
|
|
<p class="note">Since some users cannot use images at all
|
|
(e.g. because they have a very slow connection, or because they
|
|
are using a text-only browser, or because they are listening to
|
|
the page being read out by a hands-free automobile voice Web
|
|
browser, or simply because they are blind), the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute is only allowed to be
|
|
omitted rather than being provided with replacement text when no
|
|
alternative text is available and none can be made available, as
|
|
in the above examples. Lack of effort from the part of the author
|
|
is not an acceptable reason for omitting the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute.</p>
|
|
|
|
</dd>
|
|
|
|
</dl><h6 id="an-image-not-intended-for-the-user"><span class="secno">4.8.1.1.11 </span>An image not intended for the user</h6><p>Generally authors should avoid using <code><a href="#the-img-element">img</a></code> elements
|
|
for purposes other than showing images.</p><p>If an <code><a href="#the-img-element">img</a></code> element is being used for purposes other
|
|
than showing an image, e.g. as part of a service to count page
|
|
views, then the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute must
|
|
be the empty string.</p><p>In such cases, the <code title="attr-dim-width"><a href="the-map-element.html#attr-dim-width">width</a></code> and
|
|
<code title="attr-dim-height"><a href="the-map-element.html#attr-dim-height">height</a></code> attributes should both
|
|
be set to zero.</p><div class="impl">
|
|
|
|
<h6 id="guidance-for-markup-generators"><span class="secno">4.8.1.1.12 </span>Guidance for markup generators</h6>
|
|
|
|
<p>Markup generators (such as WYSIWYG authoring tools) should,
|
|
wherever possible, obtain alternative text from their
|
|
users. However, it is recognized that in many cases, this will not
|
|
be possible.</p>
|
|
|
|
<p>For images that are the sole contents of links, markup generators
|
|
should examine the link target to determine the title of the target,
|
|
or the URL of the target, and use information obtained in this
|
|
manner as the alternative text.</p>
|
|
|
|
<p>As a last resort, implementors should either set the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute to the empty string, under
|
|
the assumption that the image is a purely decorative image that
|
|
doesn't add any information but is still specific to the surrounding
|
|
content, or omit the <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute
|
|
altogether, under the assumption that the image is a key part of the
|
|
content.</p>
|
|
|
|
<p>Markup generators should generally avoid using the image's own
|
|
file name as the alternative text. Similarly, markup generators
|
|
should avoid generating alternative text from any content that will
|
|
be equally available to presentation user agents (e.g. Web
|
|
browsers).</p>
|
|
|
|
<p class="note">This is because once a page is generated, it will
|
|
typically not be updated, whereas the browsers that later read the
|
|
page can be updated by the user, therefore the browser is likely to
|
|
have more up-to-date and finely-tuned heuristics than the markup
|
|
generator did when generating the page.</p>
|
|
|
|
</div><div class="impl">
|
|
|
|
<h6 id="guidance-for-conformance-checkers"><span class="secno">4.8.1.1.13 </span>Guidance for conformance checkers</h6>
|
|
|
|
<p>A conformance checker must report the lack of an <code title="attr-img-alt"><a href="#attr-img-alt">alt</a></code> attribute as an error unless one of
|
|
the conditions listed below applies:</p>
|
|
|
|
<ul><li>The <code title="attr-title"><a href="elements.html#the-title-attribute">title</a></code> attribute is present
|
|
and has a non-empty value (as <a href="#unknown-images">described
|
|
above</a>).</li>
|
|
|
|
<li>The <code><a href="#the-img-element">img</a></code> element is in a <code><a href="grouping-content.html#the-figure-element">figure</a></code>
|
|
element that satisfies <a href="#figcaption-as-alt-condition">the
|
|
conditions described above</a>.</li>
|
|
|
|
|
|
|
|
<li>The document has a <code><a href="semantics.html#the-meta-element">meta</a></code> element with a <code title="attr-meta-name"><a href="semantics.html#attr-meta-name">name</a></code> attribute whose value is an
|
|
<a href="infrastructure.html#ascii-case-insensitive">ASCII case-insensitive</a> match for the string "<code title="meta-generator"><a href="semantics.html#meta-generator">generator</a></code>". (This case does not
|
|
represent a case where the document is conforming, only that the
|
|
generator could not determine appropriate alternative text —
|
|
validators are required to not show an error in this case to
|
|
discourage markup generators from including bogus alternative text
|
|
purely in an attempt to silence validators.)</li>
|
|
|
|
</ul></div></body></html>
|