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<h1>HTML5</h1>
<h2 class="no-num no-toc" id="a-vocabulary-and-associated-apis-for-html-and-xhtml">A vocabulary and associated APIs for HTML and XHTML</h2>
<h2 class="no-num no-toc" id="editor's-draft-date-1-january-1970">Editor's Draft 21 November 2012</h2>
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<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="content-models.html#text-content">Text content</a> in <a href="infrastructure.html#html-elements">HTML elements</a> with
child <code><a href="infrastructure.html#text-0">Text</a></code> nodes, and text in attributes of <a href="infrastructure.html#html-elements">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="references.html#refsBIDI">[BIDI]</a></p>
<p>The aforementioned restrictions are defined by specifying that
certain parts of documents form <a href="#bidirectional-algorithm-formatting-character-ranges">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="infrastructure.html#html-elements" title="HTML elements">HTML element</a> <var title="">element</var> are <a href="#bidirectional-algorithm-formatting-character-ranges">bidirectional-algorithm formatting
character ranges</a>:</p>
<ol><li><p>Let <var title="">output</var> be an empty list of strings.</li>
<li><p>Let <var title="">string</var> be an empty string.</li>
<li><p>Let <var title="">node</var> be the first child node of <var title="">element</var>, if any, or null otherwise.</li>
<!-- while node != null do -->
<li><p><i>Loop</i>: If <var title="">node</var> is null, jump to
the step labeled <i>end</i>.</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="infrastructure.html#text-0">Text</a></code> node</dt>
<dd><p>Append the text data of <var title="">node</var> to <var title="">string</var>.</dd>
<dt>If <var title="">node</var> is a <code><a href="the-br-element.html#the-br-element">br</a></code> element</dt>
<dt>If <var title="">node</var> is an <a href="infrastructure.html#html-elements" title="HTML elements">HTML element</a> that is <a href="content-models.html#flow-content-1">flow content</a> but that is not also <a href="content-models.html#phrasing-content-1">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.</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.</li>
<li><p>Jump to the step labeled <i>loop</i>.</li>
<!-- end while -->
<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>.</li>
<li><p>Return <var title="">output</var> as the
<a href="#bidirectional-algorithm-formatting-character-ranges">bidirectional-algorithm formatting character
ranges</a>.</li>
</ol><p>The value of a namespace-less attribute of an <a href="infrastructure.html#html-elements" title="HTML
elements">HTML element</a> is a <a href="#bidirectional-algorithm-formatting-character-ranges" title="bidirectional-algorithm formatting character
ranges">bidirectional-algorithm formatting character
range</a>.</p>
<!--(this is unnecessarily pedantic)
<p>The text data of a comment node is a <span
title="bidirectional-algorithm formatting character
ranges">bidirectional-algorithm formatting character
range</span>.</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="references.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="global-attributes.html#the-dir-attribute">dir</a></code> attribute, the <code><a href="the-bdo-element.html#the-bdo-element">bdo</a></code> element,
and the <code><a href="the-bdi-element.html#the-bdi-element">bdi</a></code> element, rather than maintaining the
bidirectional-algorithm formatting characters manually. The
bidirectional-algorithm formatting characters interact poorly with
CSS.</p>
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