html5/spec-author-view/requirements-relating-to-bidirectional-algorithm-formatting-characters.html - view

File: [Public] / html5 / spec-author-view / requirements-relating-to-bidirectional-algorithm-formatting-characters.html
Revision 1.129: download - view: text, annotated - select for diffs
Thu Oct 11 14:49:25 2012 UTC (12 years, 11 months ago) by mike
Branches: MAIN
CVS tags: HEAD

updated

<!doctype html> <html lang="en-US-x-Hixie"><meta content="HTML Tidy for HTML5 (experimental) for Linux/x86 http://github.com/w3c/tidy-html5/tree/c63cc39" name="generator"><meta charset="utf-8"><title>3.2.6 Requirements relating to bidirectional-algorithm formatting characters — HTML5</title><link href="style.css" rel="stylesheet"><style type="text/css"> /**/ /**/ .applies thead th > * { display: block; } .applies thead code { display: block; } .applies tbody th { white-space: nowrap; } .applies td { text-align: center; } .applies .yes { background: yellow; } .matrix, .matrix td { border: hidden; text-align: right; } .matrix { margin-left: 2em; } .dice-example { border-collapse: collapse; border-style: hidden solid solid hidden; border-width: thin; margin-left: 3em; } .dice-example caption { width: 30em; font-size: smaller; font-style: italic; padding: 0.75em 0; text-align: left; } .dice-example td, .dice-example th { border: solid thin; width: 1.35em; height: 1.05em; text-align: center; padding: 0; } td.eg { border-width: thin; text-align: center; } #table-example-1 { border: solid thin; border-collapse: collapse; margin-left: 3em; } #table-example-1 * { font-family: "Essays1743", serif; line-height: 1.01em; } #table-example-1 caption { padding-bottom: 0.5em; } #table-example-1 thead, #table-example-1 tbody { border: none; } #table-example-1 th, #table-example-1 td { border: solid thin; } #table-example-1 th { font-weight: normal; } #table-example-1 td { border-style: none solid; vertical-align: top; } #table-example-1 th { padding: 0.5em; vertical-align: middle; text-align: center; } #table-example-1 tbody tr:first-child td { padding-top: 0.5em; } #table-example-1 tbody tr:last-child td { padding-bottom: 1.5em; } #table-example-1 tbody td:first-child { padding-left: 2.5em; padding-right: 0; width: 9em; } #table-example-1 tbody td:first-child::after { content: leader(". 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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 class="prev_next"> <a href="content-models.html">&slarr; 3.2.5 Content models</a> – <a href="Overview.html#contents">Table of contents</a> – <a href="wai-aria.html">3.2.7 WAI-ARIA &srarr;</a> </div> <h4 id="requirements-relating-to-bidirectional-algorithm-formatting-characters"> <span class="secno">3.2.6</span> Requirements relating to bidirectional-algorithm formatting characters</h4> <p><a href="http://dev.w3.org/html5/spec/single-page.html#text-content" id="text-content_4">Text content</a> in <a href="http://dev.w3.org/html5/spec/single-page.html#html-elements" id="html-elements_23">HTML elements</a> with child <code><a href="http://dev.w3.org/html5/spec/single-page.html#text-0">Text</a></code> nodes, and text in attributes of <a href="http://dev.w3.org/html5/spec/single-page.html#html-elements" id="html-elements_24">HTML elements</a> that allow free-form text, may contain characters in the range U+202A to U+202E (the bidirectional-algorithm formatting characters). However, the use of these characters is restricted so that any embedding or overrides generated by these characters do not start and end with different parent elements, and so that all such embeddings and overrides are explicitly terminated by a U+202C POP DIRECTIONAL FORMATTING character. This helps reduce incidences of text being reused in a manner that has unforeseen effects on the bidirectional algorithm. <a href="http://dev.w3.org/html5/spec/single-page.html#refsBIDI">[BIDI]</a></p> <p>The aforementioned restrictions are defined by specifying that certain parts of documents form <a href="http://dev.w3.org/html5/spec/single-page.html#bidirectional-algorithm-formatting-character-ranges" id="bidirectional-algorithm-formatting-character-ranges_0">bidirectional-algorithm formatting character ranges</a>, and then imposing a requirement on such ranges.</p> <p>The strings resulting from applying the following algorithm to an <a href="http://dev.w3.org/html5/spec/single-page.html#html-elements" id="html-elements_25" title="HTML elements">HTML element</a> <var title="">element</var> are <a href="http://dev.w3.org/html5/spec/single-page.html#bidirectional-algorithm-formatting-character-ranges" id="bidirectional-algorithm-formatting-character-ranges_1">bidirectional-algorithm formatting character ranges</a>:</p> <ol><li> <p>Let <var title="">output</var> be an empty list of strings.</p> </li> <li> <p>Let <var title="">string</var> be an empty string.</p> </li> <li> <p>Let <var title="">node</var> be the first child node of <var title="">element</var>, if any, or null otherwise.</p> </li>  <li> <p><i>Loop</i>: If <var title="">node</var> is null, jump to the step labeled <i>end</i>.</p> </li> <li> <p>Process <var title="">node</var> according to the first matching step from the following list:</p> <dl class="switch"><dt>If <var title="">node</var> is a <code><a href="http://dev.w3.org/html5/spec/single-page.html#text-0">Text</a></code> node</dt> <dd> <p>Append the text data of <var title="">node</var> to <var title="">string</var>.</p> </dd> <dt>If <var title="">node</var> is a <code><a href="http://dev.w3.org/html5/spec/single-page.html#the-br-element" id="br_1">br</a></code> element</dt> <dt>If <var title="">node</var> is an <a href="http://dev.w3.org/html5/spec/single-page.html#html-elements" id="html-elements_26" title="HTML elements">HTML element</a> that is <a href="http://dev.w3.org/html5/spec/single-page.html#flow-content-1" id="flow-content_8">flow content</a> but that is not also <a href="http://dev.w3.org/html5/spec/single-page.html#phrasing-content-1" id="phrasing-content_15">phrasing content</a></dt> <dd> <p>If <var title="">string</var> is not the empty string, push <var title="">string</var> onto <var title="">output</var>, and let <var title="">string</var> be empty string.</p> </dd> <dt>Otherwise</dt> <dd>Do nothing.</dd> </dl></li> <li> <p>Let <var title="">node</var> be <var title="">node</var>'s next sibling, if any, or null otherwise.</p> </li> <li> <p>Jump to the step labeled <i>loop</i>.</p> </li>  <li> <p><i>End</i>: If <var title="">string</var> is not the empty string, push <var title="">string</var> onto <var title="">output</var>.</p> </li> <li> <p>Return <var title="">output</var> as the <a href="http://dev.w3.org/html5/spec/single-page.html#bidirectional-algorithm-formatting-character-ranges" id="bidirectional-algorithm-formatting-character-ranges_2">bidirectional-algorithm formatting character ranges</a>.</p> </li> </ol><p>The value of a namespace-less attribute of an <a href="http://dev.w3.org/html5/spec/single-page.html#html-elements" id="html-elements_27" title="HTML elements">HTML element</a> is a <a href="http://dev.w3.org/html5/spec/single-page.html#bidirectional-algorithm-formatting-character-ranges" id="bidirectional-algorithm-formatting-character-ranges_3" title="bidirectional-algorithm formatting character ranges">bidirectional-algorithm formatting character range</a>.</p>  <p>Any strings that, as described above, are <dfn id="bidirectional-algorithm-formatting-character-ranges">bidirectional-algorithm formatting character ranges</dfn> must match the <code title="">string</code> production in the following ABNF, the character set for which is Unicode. <a href="http://dev.w3.org/html5/spec/single-page.html#refsABNF">[ABNF]</a></p> <pre> string = *( plaintext ( embedding / override ) ) plaintext embedding = ( lre / rle ) string pdf override = ( lro / rlo ) string pdf lre = %x202A ; U+202A LEFT-TO-RIGHT EMBEDDING rle = %x202B ; U+202B RIGHT-TO-LEFT EMBEDDING lro = %x202D ; U+202D LEFT-TO-RIGHT OVERRIDE rlo = %x202E ; U+202E RIGHT-TO-LEFT OVERRIDE pdf = %x202C ; U+202C POP DIRECTIONAL FORMATTING plaintext = *( %x0000-2029 / %x202F-10FFFF ) ; any string with no bidirectional-algorithm formatting characters </pre> <p class="note">Authors are encouraged to use the <code title="attr-dir"><a href="http://dev.w3.org/html5/spec/single-page.html#the-dir-attribute" id="dir_15">dir</a></code> attribute, the <code><a href="http://dev.w3.org/html5/spec/single-page.html#the-bdo-element" id="bdo_2">bdo</a></code> element, and the <code><a href="http://dev.w3.org/html5/spec/single-page.html#the-bdi-element" id="bdi_4">bdi</a></code> element, rather than maintaining the bidirectional-algorithm formatting characters manually. The bidirectional-algorithm formatting characters interact poorly with CSS.</p>