csswg-drafts/css3-text/Overview.src.html at 531f7678a25e90cee375c2e3ae3b9da44567a784 · w3c/csswg-drafts · GitHub

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<!DOCTYPE html public '-//W3C//DTD HTML 4.01//EN'
  'http://www.w3.org/TR/html4/strict.dtd'>
<html lang="en">
<head>
  <meta http-equiv="Content-Type" content="text/html; charset=utf-8">
  <title>CSS Text Level 3</title>
  <link rel="stylesheet" type="text/css" href="../default.css">

  <style type="text/css">
    .egbidiwsaA,.egbidiwsbB,.egbidiwsaB,.egbidiwsbC
      { white-space:pre;font-size:80%;font-family:monospace; vertical-align:2px; margin:1px }
    .egbidiwsaA { background:lime;padding:2px; }
    .egbidiwsbB { border:2px solid blue }
    .egbidiwsaB { background:yellow;border:2px dotted white }
    .egbidiwsbC { border:2px dotted red }

    .char { border: 1px dotted gray; }
    .quarter { font-size: 25%; }
    tt[lang="ja"] { font-family: "MS Gothic", "Osaka", monospace }
  </style>

  <link rel="stylesheet" type="text/css" href="http://www.w3.org/StyleSheets/TR/W3C-ED.css">
</head>

<body>

<div class="head">

<!--logo-->

<h1>CSS Text Level 3</h1>

<h2 class="no-num no-toc">[LONGSTATUS] [DATE]</h2>

<dl>
  <dt>This version:</dt>
      <dd><a href="http://dev.w3.org/csswg/css3-text/">$Date$ (CVS $Revision$)</a>
    <!--
      <dd><a href="http://www.w3.org/TR/[YEAR]/WD-css3-text-[CDATE]/">http://www.w3.org/TR/[YEAR]/WD-css3-text-[CDATE]/</a></dd>
    -->
  <dt>Latest version:</dt>
    <dd><a href="http://www.w3.org/TR/css3-text">http://www.w3.org/TR/css3-text</a></dd>
  <dt>Latest editor's draft:</dt>
    <dd><a href="http://dev.w3.org/csswg/css3-text/">http://dev.w3.org/csswg/css3-text/</a></dd>
  <dt>Previous version:</dt>
    <dd><a
      href="http://www.w3.org/TR/2011/WD-css3-text-20110901/">http://www.w3.org/TR/2011/WD-css3-text-20110901/</a></dd>
  <dt>Editors:</dt>
    <dd><a href="http://fantasai.inkedblade.net/contact">Elika J. Etemad</a> (Mozilla)</dd>
    <dd><a href="mailto:kojiishi@gluesoft.co.jp">Koji Ishii</a> (Invited Expert)</dd>
    <dd><a href="mailto:murakami@antenna.co.jp">Shinyu Murakami</a> (<a href="http://www.antenna.co.jp/">Antenna House</a>)</dd>
</dl>

<!--begin-copyright-->
<p>[Here will be included the file "../copyright.inc"]</p>
<!--end-copyright-->

<hr title="Separator for header">
</div>

<h2 class="no-num no-toc" id="abstract">Abstract</h2>

  <p>This CSS3 module defines properties for text manipulation and
    specifies their processing model. It covers line breaking, justification
    and alignment, white space handling, text decorati
686C
on and text
    transformation.</p>

<h2 class="no-num no-toc" id="status">Status of This Document</h2>

  <p><em>This section describes the status of this document at the time of
   its publication. Other documents may supersede this document. A list of
   current W3C publications and the latest revision of this technical report
   can be found in the <a href="http://www.w3.org/TR/">W3C technical reports
   index at http://www.w3.org/TR/.</a></em>

  <p>Publication as a Working Draft does not imply endorsement by the W3C
   Membership. This is a draft document and may be updated, replaced or
   obsoleted by other documents at any time. It is inappropriate to cite this
   document as other than work in progress.

  <p>This CSS module has been produced as a combined effort of the <a
    href="http://www.w3.org/International/Activity">W3C Internationalization Activity</a>,
    and the <a href="http://www.w3.org/Style/Activity">Style Activity</a> and is maintained
    by the <a href="http://www.w3.org/Style/CSS/members">CSS Working Group</a>. It also
    includes contributions made by participants in the <a
    href="http://www.w3.org/Style/XSL/Group/">XSL Working Group</a> (<a
    href="http://cgi.w3.org/MemberAccess/AccessRequest">members
    only</a>).

  <p>This document was produced by a group operating under the <a
   href="http://www.w3.org/Consortium/Patent-Policy-20040205/">5 February
   2004 W3C Patent Policy</a>. W3C maintains a <a
   href="http://www.w3.org/2004/01/pp-impl/32061/status"
   rel=disclosure>public list of any patent disclosures</a> made in
   connection with the deliverables of the group; that page also includes
   instructions for disclosing a patent. An individual who has actual
   knowledge of a patent which the individual believes contains <a
   href="http://www.w3.org/Consortium/Patent-Policy-20040205/#def-essential">Essential
   Claim(s)</a> must disclose the information in accordance with <a
   href="http://www.w3.org/Consortium/Patent-Policy-20040205/#sec-Disclosure">section
   6 of the W3C Patent Policy</a>.</p>

  <p><strong>Feedback on this draft should be posted to the
    (<a href="http://lists.w3.org/Archives/Public/www-style/">archived</a>)
    public mailing list <a href="mailto:www-style@w3.org">www-style@w3.org</a></strong>
    (see <a href="http://www.w3.org/Mail/Request">instructions</a>) <strong>with
    <kbd>[css3-text]</kbd> in the subject line.</strong>
    You are strongly encouraged to complain if you see something stupid
    in this draft. The editors will do their best to respond to all feedback.</p>

  <p><strong>If you have implemented properties from the
    <a href="http://www.w3.org/TR/2003/CR-css3-text-20030514/">May 2003
    CSS3 Text CR</a></strong>
    <em>please</em> let us know so we can take that into account as
    we redraft the spec. You can post to
    <a href="http://lists.w3.org/Archives/Public/www-style/">www-style</a> (public),
    post to the <a href="http://lists.w3.org/Archives/Member/w3c-css-wg/">CSS WG mailing list</a>
    (<a href="http://cgi.w3.org/MemberAccess/AccessRequest">Member-restricted</a>),
    or <a href="http://fantasai.inkedblade.net/contact">email fantasai directly</a> (personal).</p>

  <p>The following features are at risk and may be cut from the spec during
    its CR period if there are no (correct) implementations:</p>
    <ul>
      <li>the &lt;length> values of the 'tab-size' property
      <li>the 'hanging-punctuation' property
      <li>the percentage values of 'letter-spacing' and 'word-spacing'
      <li>the 'hyphenate-limit-*' properties
      <li>the 'text-spacing' property
      <li>the 'text-decoration-skip' property / ''ink'' value
      <li>the 'text-emphasis-skip' property
      <li><span class="issue">audit draft and add more here</span>
    </ul>

<h2 class="no-num no-toc" id="contents">Table of Contents</h2>

<!--toc-->

<h2 id="intro">
  Introduction</h2>

  <p>[document here]</p>

  <p class="issue">This draft describes features that are specific to certain scripts.
  There is an ongoing discussion about where these features belong: in
  existing CSS properties, in new CSS properties, or perhaps in other
  specifications.


<h3 id="placement">
Module Interactions</h3>

  <p>This module replaces and extends the text-level
  features defined in [[!CSS21]] chapter 16.

<h3 id="values">
Values</h3>

  <p>This specification follows the
  <a href="http://www.w3.org/TR/CSS21/about.html#property-defs">CSS property
  definition conventions</a> from [[!CSS21]]. Value types not defined in
  this specification are defined in CSS Level 2 Revision 1 [[!CSS21]].
  Other CSS modules may expand the definitions of these value types: for
  example [[CSS3COLOR]], when combined with this module, expands the
  definition of the &lt;color&gt; value type as used in this specification.</p>

  <p>In addition to the property-specific values listed in their definitions,
  all properties defined in this specification also accept the
  <a href="http://www.w3.org/TR/CSS21/cascade.html#value-def-inherit">inherit</a>
  keyword as their property value. For readability it has not been repeated
  explicitly.

<h3 id="terms">
Terminology</h3>

  <p id="grapheme-cluster">A <dfn>grapheme cluster</dfn> is what
    a language user considers to be a character or a basic unit of the
    script. The term is described in detail in the Unicode Technical
    Report: Text Boundaries [[!UAX29]]. This specification uses the
    <em>extended grapheme cluster</em> definition in [[!UAX29]] (not
    the <em>legacy grapheme cluster</em> definition). The UA may further
    tailor the definition as allowed by Unicode. Within this specification,
    the ambiguous term <dfn>character</dfn> is used as a friendlier synonym
    for <i>grapheme cluster</i>.
    See <a href="http://dev.w3.org/csswg/css3-writing-modes/#character-properties">Characters and Properties</a>
    for how to determine the Unicode properties of a character.

  <p id="letter">A <dfn>letter</dfn> for the purpose of this specification
    is a <i>character</i> belonging to one of the Letter or Number general
    categories in Unicode. [[!UAX44]]

<h2 id="transforming">
  Transforming Text</h2>

  <h3 id="text-transform">
    <a name="caps-prop"></a>
    Transforming Text: the 'text-transform' property</h3>

    <table class="propdef">
      <tbody>
        <tr>
          <th>Name:</th>
          <td><dfn>text-transform</dfn></td>
        </tr>
        <tr>
          <th>Value:</th>
          <td>none |
            [ [ capitalize | uppercase | lowercase ] || full-width || full-size-kana ]
          </td>
        </tr>
        <tr>
          <th>Initial:</th>
          <td>none</td>
        </tr>
        <tr>
          <th>Applies to:</th>
          <td>all elements</td>
        </tr>
        <tr>
          <th>Inherited:</th>
          <td>yes</td>
        </tr>
        <tr>
          <th>Percentages:</th>
          <td>N/A</td>
        </tr>
        <tr>
          <th>Media:</th>
          <td>visual</td>
        </tr>
        <tr>
          <th>Computed&#160;value:</th>
          <td>as specified</td>
        </tr>
      </tbody>
    </table>

    <p>This property transforms text for styling purposes.
      Values have the following meanings:</p>

    <dl>
      <dt><dfn title="text-transform:none">''none''</dfn></dt>
        <dd>No effects.</dd>
      <dt><dfn title="text-transform:capitalize">''capitalize''</dfn></dt>
        <dd>Puts the first <i>letter</i> of each word in titlecase; other characters
          are unaffected.</dd>
      <dt><dfn title="text-transform:uppercase">''uppercase''</dfn></dt>
        <dd>Puts all characters in uppercase.
      <dt><dfn title="text-transform:lowercase">''lowercase''</dfn></dt>
        <dd>Puts all characters in lowercase.</dd>
      <dt><dfn title="text-transform:full-width">''full-width''</dfn></dt>
        <dd>Puts all characters in fullwidth form.
          If the character does not have a corresponding fullwidth form,
          it is left as is.
          This value is typically used to typeset Latin characters and digits
          like ideographic characters.
      <dt><dfn title="text-transform:full-size-kana">''full-size-kana''</dfn></dt>
        <dd>Converts all small Kana characters to normal Kana.
          This value is typically used for ruby annotation text,
          where all small Kana should be drawn as large Kana.
    </dl>

    <p>The case mapping rules for the character repertoire specified by the
      Unicode Standard can be found on the Unicode Consortium Web site
      [[!UNICODE]]. The UA must use the full case mappings for Unicode
      characters, including any conditional casing rules, as defined in
      Default Case Algorithm section. If (and only if) the content language
      of the element is, according to the rules of the document language,
      known, then any appropriate language-specific rules must be applied
      as well.
      These minimally include, but are not limited to, the language-specific
      rules in Unicode's
      <a href="http://www.unicode.org/Public/UNIDATA/SpecialCasing.txt">SpecialCasing.txt</a>.

    <div class="example">
      <p>For example, in Turkish there are two &ldquo;i&rdquo;s, one with
        a dot&mdash;&ldquo;İ&rdquo; and &ldquo;i&rdquo;&mdash; and one
        without&mdash;&ldquo;I&rdquo; and &ldquo;ı&rdquo;. Thus the usual
        case mappings between &ldquo;I&rdquo; and &ldquo;i&rdquo; are
        replaced with a different set of mappings to their respective
        undotted/dotted counterparts, which do not exist in English. This
        mapping must only take effect if the language is known to be Turkish
        or Azeri; in other languages, the usual mapping of &ldquo;I&rdquo;
        and &ldquo;i&rdquo; is required. This rule is thus conditionally
        defined in Unicode's SpecialCasing.txt file.
    </div>

<!--
    <div class="example">
      <p>An example where the UA may choose to include rules beyond those
        in Unicode is Greek. In Greek, if the entire word is in upper case,
        accents are dropped or transformed
       http://blogs.msdn.com/b/michkap/archive/2006/08/18/706383.aspx
    </div>
-->

    <p>The definition of "word" used for ''capitalize'' is UA-dependent;
      [[!UAX29]] is suggested (but not required) for determining such word
      boundaries. Authors should not expect ''capitalize'' to follow
      language-specific titlecasing conventions (such as skipping articles
      in English).

    <p>The definition of fullwidth and halfwidth forms can be found on the
      Unicode consortium web site at [[!UAX11]].
      The mapping to fullwidth form is defined by taking code points with
      the &lt;wide&gt; or the &lt;narrow&gt; tag in their Decomposition_Mapping
      in [[!UAX44]]. For the &lt;narrow&gt; tag, the mapping is from the code
      point to the decomposition (minus &lt;narrow&gt; tag), and for the
      &lt;wide&gt; tag, the mapping is from the decomposition (minus the
      &lt;wide&gt; tag) back to the original code point.</p>

    <p>The mappings for small Kana to normal Kana are defined in
      <a href="#small-kana">Small Kana Mappings</a>.</p>

    <p>When multiple values are specified and therefore multiple
      transformations need to be applied, they are applied in the following
      order:</p>
    <ol>
      <li>''capitalize'', ''uppercase'', and ''lowercase''</li>
      <li>''full-width''</li>
      <li>''full-size-kana''</li>
    </ol>

    <p>Text transformation happens after <a href="#white-space-rules">white
      space processing</a>, which means that ''full-width'' transforms
      only preserved U+0020 spaces to U+3000.

    <div class="example">
      <p>The following example converts the ASCII characters in abbreviations
        in Japanese to their fullwidth variants so that they lay out and line
        break like ideographs:
      <pre>abbr:lang(ja) { text-transform: full-width; }</pre>
    </div>

    <p class="issue">All-caps text sometimes has special typographic considerations.
      For example: Punctuation and number glyphs might be adjusted for the
      higher "center of gravity" (see the
        <a href="http://www.microsoft.com/typography/otspec/features_ae.htm#case">case</a>
      feature in OpenType). Should we turn that on by default, as they suggest?</p>

    <p class="note">A future level of CSS may introduce the ability to create
      custom mapping tables for less common text transforms, such as by
      ''@text-transform'' rule similar to ''@counter-style'' from [[CSS3LIST]].

<h2 id="white-space-processing">
  White Space Processing</h2>

  <p>The source text of a document often contains formatting that
    is not relevant to the final rendering: for example, breaking
    the source into segments (lines) for ease of editing or adding
    white space characters such as tabs and spaces to indent the
    source code. CSS white space processing allows the author to
    control interpretation of such formatting: to preserve or
    collapse it away when rendering the document.

  <p id="segment-normalization">
    In the document source, segments can be delimited by carriage
    returns (U+000D), linefeeds (U+000A) or a combination (U+000D U+000A),
    or by some other mechanism, such as the SGML RECORD-START
    and RECORD-END tokens.

    If no segmentation rules are specified for the document language,
    each line feed (U+000A), carriage return (U+000D) and CRLF sequence
    (U+000D U+000A) in the text is considered a segment break. (This
    default rule also applies to generated content.)

    In CSS, each such segment break is treated as a single line feed
    character (U+000A).

  <p>White space processing in CSS interprets white space characters
    only for rendering: it has no effect on the underlying document data.

  <p class="note">Note that the document parser may have not only normalized
    segment breaks, but also collapsed other space characters or
    otherwise processed white space according to markup rules. Because CSS
    processing occurs <em>after</em> the parsing stage, it is not possible
    to restore these characters for styling. Therefore, some of the
    behavior specified below can be affected by these limitations and
    may be user agent dependent.</p>

  <p>Control characters (Unicode class Cc) other than tab (U+0009), line feed
    (U+000A), space (U+0020), and the bidi formatting characters (U+202<var>x</var>)
    should be rendered as invisible zero-width characters. UAs may instead treat
    them as visible characters. (Note, however, that this will usually result in
    them being rendered as missing glyphs.)
    <span class="issue">What's the line-breaking behavior? Effects on joining?
    Can we just copy the behavior of some zero-width Unicode character?</span>

  <h3 id="white-space-collapsing">
    White Space Collapsing: the 'text-space-collapse' property</h3>

    <p class="issue">This section is still under discussion and may change in future drafts.</p>

    <table class="propdef">
      <tbody>
        <tr>
          <th>Name:</th>
          <td><dfn>text-space-collapse</dfn></td>
        </tr>
        <tr>
          <th>Value:</th>
          <td>collapse | discard | [ [preserve | preserve-breaks] && [ trim-inner || consume-before || consume-after ]</td>
        </tr>
        <tr>
          <th>Initial:</th>
          <td>collapse</td>
        </tr>
        <tr>
          <th>Applies to:</th>
          <td>all elements</td>
        </tr>
        <tr>
          <th>Inherited:</th>
          <td>yes</td>
        </tr>
        <tr>
          <th>Percentages:</th>
          <td>N/A</td>
        </tr>
        <tr>
          <th>Media:</th>
          <td>visual</td>
        </tr>
        <tr>
          <th>Computed&#160;value:</th>
          <td>specified value</td>
        </tr>
      </tbody>
    </table>

    <p class="issue">Need a property name</p>

    <p>This property declares whether and how
      <a href="#white-space-processing">white space</a> inside the element is
      collapsed. Values have the following meanings, which must be interpreted
      according to the <a href="#white-space-rules">white space processing
      rules</a>:</p>

    <dl>
      <dt><dfn title="white-space:collapse">''collapse''</dfn></dt>
      <dd>This value directs user agents to collapse sequences of white space
        into a single character (or <a href="#line-break-transform">in some
        cases</a>, no character).</dd>
      <dt><dfn title="white-space:preserve">''preserve''</dfn></dt>
      <dd>This value prevents user agents from collapsing sequences
      of white space. Line feeds are preserved as forced line breaks.</dd>
      <dt><dfn title="white-space:preserve-breaks">''preserve-breaks''</dfn></dt>
      <dd>This value collapses white space as for ''collapse'', but preserves
        line feeds as forced line breaks.</dd>
      <dt><dfn title="white-space:discard">''discard''</dfn></dt>
      <dd>This value directs user agents to "discard" all white space in the
        element.
      <dt><dfn title="white-space:trim-inner">''trim-inner''</dfn></dt>
      <dd>For block containers this value directs UAs to discard all whitespace
        at the beginning of the element up to and including the last line feed
        before the first non-white-space character in the element as well as
        to discard all white space at the end of the element starting with the
        first line feed after the last non-white-space character in the element.
        For other elements this value directs UAs to discard all whitespace
        at the beginning and end of the element.</dd>
      <dt><dfn title="white-space:consume-before">''consume-before''</dfn></dt>
      <dd>This value directs the UA to collapse all collapsible whitespace
        immediately before the start of the element.
      <dt><dfn title="white-space:consume-after">''consume-after''</dfn></dt>
      <dd>This value directs the UA to collapse all collapsible whitespace
        immediately after the end of the element.
    </dl>

    <div class="example">
      <p>The following style rules implement MathML's white space processing:
      <pre>
<!-- -->@namespace m "http://www.w3.org/1998/Math/MathML";
<!-- -->m|* {
<!-- -->  text-space-collapse: discard;
<!-- -->}
<!-- -->m|mi, m|mn, m|mo, m|ms, m|mtext {
<!-- -->  text-space-collapse: trim-inner;
<!-- -->}</pre>
    </div>

    <p class="issue">It's been pointed out that ''trim-inner'', ''consume-before'',
    and ''consume-after'' won't work well because 'text-space-collapse' is
    inherited, meaning that inserting a &lt;span> or &gt;div> would cause more
    white space to be removed than otherwise.

  <h3 id="tab-size">
    Tab Character Size: the 'tab-size' property</h3>

    <table class="propdef">
      <tbody>
        <tr>
          <th>Name:</th>
          <td><dfn>tab-size</dfn></td>
        </tr>
        <tr>
          <th>Value:</th>
          <td>&lt;integer&gt; | &lt;length&gt;</td>
        </tr>
        <tr>
          <th>Initial:</th>
          <td>8</td>
        </tr>
        <tr>
          <th>Applies to:</th>
          <td>block containers</td>
        </tr>
        <tr>
          <th>Inherited:</th>
          <td>yes</td>
        </tr>
        <tr>
          <th>Percentages:</th>
          <td>N/A</td>
        </tr>
        <tr>
          <th>Media:</th>
          <td>visual</td>
        </tr>
        <tr>
          <th>Computed&#160;value:</th>
          <td>specified value</td>
        </tr>
      </tbody>
    </table>

    <p>This property determines the measure of the tab character (U+0009)
      when rendered. Integers represent the measure in space characters (U+0020).
      Negative integers are not allowed.

  <h3 id="white-space-rules">
    The White Space Processing Rules</h3>

    <p>White space processing affects only spaces (U+0020), tabs (U+0009),
      and (<a href="#segment-normalization">post-normalization</a>)
      line feeds (U+00A0).

    <p>For each inline (including anonymous inlines) within an inline
      formatting context, white space characters are handled as follows,
      ignoring bidi formatting characters as if they were not there:</p>

    <ul>
    <li id="collapse"><p>If 'text-space-collapse'
      is set to ''collapse'' or ''preserve-breaks'', white space characters
      are considered <dfn>collapsible</dfn> and are processed by
      performing the following steps:</p>
      <ol>
        <li>All spaces and tabs immediately preceding or following a line
          feed character are removed.</li>
        <li>If 'text-space-collapse' is not
          ''preserve-breaks'', line feed characters are transformed for
          rendering according to the <a href="#line-break-transform">line
          feed transformation rules</a>.
        </li>
        <li>Every tab is converted to a space (U+0020).</li>
        <li>Any space immediately following another collapsible space
          &mdash;even one outside the boundary of the inline&mdash;is
          removed.
          However, if removing this space would eliminate a line breaking
          opportunity in the text, that opportunity is still considered
          to exist.</li>
        <li>A collapsible space immediately preceding an element with
          ''consume-before'' is removed. Such removed spaces do not indicate
          a line breaking opportunity in the text.
        <li>Any collapsible spaces after the end of an element with
         
E902
 ''consume-after'' are removed. Such removed spaces do not indicate
          a line breaking opportunity in the text.
      </ol>
    </li>
    <li><p>If 'text-space-collapse' is set to
      ''preserve'', any sequence of spaces unbroken by an element
      boundary is treated as a sequence of non-breaking spaces. However,
      a line breaking opportunity exists at the end of the sequence.</p></li>
    <li><p>If 'text-space-collapse' is set to
      ''discard'', the first white space character in every white space
      sequence is converted to a zero width non-joiner (U+200C) and
      the rest of the sequence is removed.</p>
    </ul>

    <p>Then, the entire block is rendered. Inlines are laid out, taking bidi
      reordering into account, and wrapping as specified by the
      'text-wrap' property.</p>

    <p>As each line is laid out,</p>
    <ol>
      <li>A sequence of collapsible spaces at the beginning of a line is
        removed.
      <li>Each tab is rendered as a horizontal shift that lines up
        the start edge of the next glyph with the next tab stop.
        Tab stops occur at points that are multiples of the width of a
        space (U+0020) rendered in the block's font from the block's
        starting content edge. How many spaces is given by the 'tab-size'
        property.</li>
      <li>A sequence of collapsible spaces at the end of a line is removed.
      <li>If spaces or tabs at the end of a line are non-collapsible but
         have 'text-wrap' set to 'normal' or 'avoid' the UA may visually
         collapse their character advance widths.
    </ol>

    <p>White space that was not removed during the white space processing
      steps is called <dfn>preserved</dfn> white space.</p>

    <div class="example">
    <h4 id="egbidiwscollapse">
      Example of bidirectionality with white space collapsing</h4>

      <p>Consider the following markup fragment, taking special note of spaces
        (with varied backgrounds and borders for emphasis and identification):
        </p>
      <pre><code>&lt;ltr&gt;A<span class="egbidiwsaA">&#160;</span>&lt;rtl&gt;<span class="egbidiwsbB">&#160;</span>B<span class="egbidiwsaB">&#160;</span>&lt;/rtl&gt;<span class="egbidiwsbC">&#160;</span>C&lt;/ltr&gt;</code></pre>

      <p>where the <code>&lt;ltr&gt;</code> element represents a left-to-right
        embedding and the <code>&lt;rtl&gt;</code> element represents a
        right-to-left embedding. If the 'text-space-collapse' property is set
        to ''collapse'', the above processing model would result in the
        following:</p>

      <ul style="line-height:1.3">
        <li>The space before the B (<span class="egbidiwsbB">&#160;</span>)
          would collapse with the space after the A (<span
          class="egbidiwsaA">&#160;</span>).</li>
        <li>The space before the C (<span class="egbidiwsbC">&#160;</span>)
          would collapse with the space after the B (<span
          class="egbidiwsaB">&#160;</span>).</li>
      </ul>

      <p>This would leave two spaces, one after the A in the left-to-right
        embedding level, and one after the B in the right-to-left embedding
        level. This is then ordered according to the Unicode bidirectional
        algorithm, with the end result being:</p>

      <pre>A<span class="egbidiwsaA">&#160;</span><span class="egbidiwsaB">&#160;</span>BC</pre>

      <p>Note that there are two spaces between A and B, and none between B
        and C. This is best avoided by putting spaces outside the element
        instead of just inside the opening and closing tags and, where
        practical, by relying on implicit bidirectionality instead of explicit
        embedding levels.</p>
    </div>

    <h4 id="line-break-transform">
      Line Feed Transformation Rules</h4>

      <p>When line feeds are <a href="#collapse">collapsible</a>, they are
        either transformed into a space (U+0020) or removed depending on the
        context before and after the line break.</p>

      <p class="note">Note that the white space processing rules have already
        removed any tabs and spaces after the line feed before these checks
        take place.</p>

      <ul>
        <li>If the character immediately before or immediately after the line
          feed is the zero width space character (U+200B), then the line feed
          is removed.
        <li>Otherwise, if the East Asian Width property [[!UAX11]] of both
          the character before and after the line feed is F, W, or H (not A),
          and neither side is Hangul,
          then the line feed is removed.
        <li>Otherwise, the line feed is converted to a space (U+0020).
      </ul>

      <p class="issue">Comments on how well this would work in practice would
        be very much appreciated, particularly from people who work with
        Thai and similar scripts.</p>

    <h4 id="white-space-summary">
      Informative Summary of White Space Collapsing Effects</h4>

      <ul>
        <li>Consecutive white space collapses into a single space.
        <li>A sequence of newlines and other white space between two
          Chinese, Japanese, or Yi characters collapses into nothing.
        <li>A zero width space before or after a white space sequence
          containing a newline causes the entire sequence of white space
          to collapse into a zero width space.
      </ul>

  <h3 id="white-space">
    White Space and Text Wrapping Shorthand: the 'white-space' property</h3>

    <table class="propdef">
      <tbody>
        <tr>
          <th>Name:</th>
          <td><dfn>white-space</dfn></td>
        </tr>
        <tr>
          <th>Value:</th>
          <td>normal | pre | nowrap | pre-wrap | pre-line</td>
        </tr>
        <tr>
          <th>Initial:</th>
          <td>not defined for shorthand properties</td>
        </tr>
        <tr>
          <th>Applies to:</th>
          <td>all elements</td>
        </tr>
        <tr>
          <th>Inherited:</th>
          <td>yes</td>
        </tr>
        <tr>
          <th>Percentages:</th>
          <td>N/A</td>
        </tr>
        <tr>
          <th>Media:</th>
          <td>visual</td>
        </tr>
        <tr>
          <th>Computed&#160;value:</th>
          <td>see individual properties</td>
        </tr>
      </tbody>
    </table>

    <p>The 'white-space' property is a shorthand for the
      'text-space-collapse' and 'text-wrap' properties.
      Not all combinations are represented.
      Values have the following meanings:</p>

    <dl>
      <dt><dfn title="white-space:normal">''normal''</dfn></dt>
      <dd>Sets 'text-space-collapse' to ''collapse'' and
        'text-wrap' to ''normal''</dd>
      <dt><dfn title="white-space:pre">''pre''</dfn></dt>
      <dd>Sets 'text-space-collapse' to ''preserve'' and
        'text-wrap' to ''none''</dd>
      <dt><dfn title="white-space:nowrap">''nowrap''</dfn></dt>
      <dd>Sets 'text-space-collapse' to ''collapse'' and
        'text-wrap' to ''none''</dd>
      <dt><dfn title="white-space:pre-wrap">''pre-wrap''</dfn></dt>
      <dd>Sets 'text-space-collapse' to ''preserve'' and
        'text-wrap' to ''normal''</dd>
      <dt><dfn title="white-space:pre-line">''pre-line''</dfn></dt>
      <dd>Sets 'text-space-collapse' to ''preserve-breaks'' and
        'text-wrap' to ''normal''</dd>
    </dl>

    <p>The following informative table summarizes the behavior of various
      'white-space' values:</p>

    <table class="data">
      <colgroup class="header"></colgroup>
      <colgroup span=3></colgroup>
      <thead>
        <tr>
          <th></th>
          <th>New Lines</th>
          <th>Spaces and Tabs</th>
          <th>Text Wrapping</th>
        </tr>
      </thead>
      <tbody>
        <tr>
          <th>normal</th>
          <td>Collapse</td>
          <td>Collapse</td>
          <td>Wrap</td>
        </tr>
        <tr>
          <th>pre</th>
          <td>Preserve</td>
          <td>Preserve</td>
          <td>No wrap</td>
        </tr>
        <tr>
          <th>nowrap</th>
          <td>Collapse</td>
          <td>Collapse</td>
          <td>No wrap</td>
        </tr>
        <tr>
          <th>pre-wrap</th>
          <td>Preserve</td>
          <td>Preserve</td>
          <td>Wrap</td>
        </tr>
        <tr>
          <th>pre-line</th>
          <td>Preserve</td>
          <td>Collapse</td>
          <td>Wrap</td>
      </tbody>
    </table>

<h2 id="line-breaking">
  Line Breaking and Word Boundaries</h2>

  <p>In most writing systems, in the absence of hyphenation a line break occurs
    only at word boundaries. Many writing systems use spaces or
    punctuation to explicitly separate words, and line break opportunities
    can be identified by these characters. Scripts such as Thai, Lao, and
    Khmer, however, do not use spaces or punctuation to separate words.
    Although the zero width space (U+200B) can be used as an explicit word
    delimiter in these scripts, this practice is not common. As a result,
    a lexical resource is needed to correctly identify break points in such
    texts.

  <p>In several other writing systems, (including Chinese, Japanese, Yi,
    and sometimes also Korean) a line break opportunity is based on
    character boundaries, not word boundaries. In these systems a line can break
    anywhere <em>except</em> between certain character combinations.
    Additionally the level of strictness in these restrictions can vary
    with the typesetting style.</p>

  <p>CSS does not fully define where line breaking opportunities occur,
    however some controls are provided to distinguish common variations.

  <p class="note">Further information on line breaking conventions can be
      found in
      [[JLREQ]] and [[JIS4051]] for Japanese,
      [[ZHMARK]] for Chinese, and
      in [[!UAX14]] for all scripts in Unicode.
      <!-- The CSS Working Group notes that although UAX 14 contains a wealth of
  
5DD0
    information about line breaking conventions, a literal implementation
      of its algorithm has been found to be inadequate in multiple situations. --></p>

  <p class="issue">Any guidance for appropriate references here would be
    much appreciated.</p>

  <p class="issue">Information on line-breaking in the absence of dictionaries:
    <a href="http://lists.w3.org/Archives/Public/www-style/2011Feb/0126.html">for Thai</a>

  <p>Floated and absolutely-positioned elements do not introduce a line
    breaking opportunity. The line breaking behavior of a replaced element
    is equivalent to that of a Latin character.</p>

  <p class="issue">It is not clear whether this section handles Southeast Asian
    scripts well. Additionally, some guidance should be provided on how to
    break or not break Southeast Asian in the absence of a dictionary.</p>

  <h3 id="line-break">
    Line Breaking Strictness: the 'line-break' property</h3>

    <table class="propdef">
      <tbody>
        <tr>
          <th>Name:</th>
          <td><dfn>line-break</dfn></td>
        </tr>
        <tr>
          <th>Value:</th>
          <td>auto | loose | normal | strict</td>
        </tr>
        <tr>
          <th>Initial:</th>
          <td>auto</td>
        </tr>
        <tr>
          <th>Applies to:</th>
          <td>all elements</td>
        </tr>
        <tr>
          <th>Inherited:</th>
          <td>yes</td>
        </tr>
        <tr>
          <th>Percentages:</th>
          <td>N/A</td>
        </tr>
        <tr>
          <th>Media:</th>
          <td>visual</td>
        </tr>
        <tr>
          <th>Computed&#160;value:</th>
          <td>specified value</td>
        </tr>
      </tbody>
    </table>

    <p>This property specifies the strictness of line-breaking rules applied
      within an element: particularly how line-breaking interacts with
      punctuation. Values have the following meanings:</p>

    <dl>
      <dt><dfn title="line-break:auto">''auto''</dfn></dt>
      <dd>The UA determines the set of line-breaking restrictions to use,
        and it may vary the restrictions based on the length of the line; e.g.,
        use a less restrictive set of line-break rules for short lines.</dd>
      <dt><dfn title="line-break:loose">''loose''</dfn></dt>
      <dd>Breaks text using the least restrictive set of line-breaking
        rules. Typically used for short lines, such as in newspapers.</dd>
      <dt><dfn title="line-break:normal">''normal''</dfn></dt>
      <dd>Breaks text using the most common set of line-breaking rules.</dd>
      <dt><dfn title="line-break:strict">''strict''</dfn></dt>
      <dd>Breaks text using the most stringent set of line-breaking
        rules.</dd>
    </dl>

    <p>CSS distinguishes between three levels of strictness in the rules for
      implicit line breaking. The precise set of rules in effect for each
      level is up to the UA and should follow language conventions. However,
      this specification does recommend that:</p>

    <ul>
      <li>Following breaks be forbidden in ''strict'' line breaking and
        allowed in ''normal'' and ''loose'':
        <ul>
          <li>breaks before Japanese <a href="#small-kana">small kana</a>
          <li>breaks before the Katakana-Hiragana prolonged sound mark:
            &#x30FC;&nbsp;U+30FC
        </ul>
        If the language is known to be Chinese or Japanese, then additionally:
        <ul>
          <li>breaks before before hyphens:<br>
            &#x2010;&nbsp;U+2010,  &#x2013;&nbsp;U+2013,  &#x301C;&nbsp;U+301C,
            &#x30A0;&nbsp;U+30A0
        </ul>
      <li>Following breaks be forbidden in ''normal'' and ''strict'' line
        breaking and allowed in ''loose'':
        <ul>
          <li>breaks before iteration marks:<br>
            &#x3005;&nbsp;U+3005,  &#x303B;&nbsp;U+303B,  &#x309D;&nbsp;U+309D,
            &#x309E;&nbsp;U+309E,  &#x30FD;&nbsp;U+30FD,  &#x30FE;&nbsp;U+30FE
          <li>breaks between some inseparable characters:<br>
            &#x2025;&nbsp;U+2025,  &#x2026;&nbsp;U+2026
        </ul>
        If the language is known to be Chinese or Japanese, then additionally:
        <ul>
          <li>breaks before certain centered punctuation marks:<br>
            &#x003A;&nbsp;U+003A,  &#x003B;&nbsp;U+003B,  &#x30FB;&nbsp;U+30FB,
            &#xFF1A;&nbsp;U+FF1A,  &#xFF1B;&nbsp;U+FF1B,  &#xFF65;&nbsp;U+FF65,
            &#x0021;&nbsp;U+0021,  &#x003F;&nbsp;U+003F,  &#x203C;&nbsp;U+203C,
            &#x2047;&nbsp;U+2047,  &#x2048;&nbsp;U+2048,  &#x2049;&nbsp;U+2049,
            &#xFF01;&nbsp;U+FF01,  &#xFF1F;&nbsp;U+FF1F
          <li>breaks before postfixes:<br>
            &#x0025;&nbsp;U+0025,  &#x00A2;&nbsp;U+00A2,  &#x00B0;&nbsp;U+00B0,
            &#x2030;&nbsp;U+2030,  &#x2032;&nbsp;U+2032,  &#x2033;&nbsp;U+2033,
            &#x2103;&nbsp;U+2103,  &#xFF05;&nbsp;U+FF05,  &#xFFE0;&nbsp;U+FFE0
          <li>breaks after prefixes:<br>
            &#x0024;&nbsp;U+0024,  &#x00A3;&nbsp;U+00A3,  &#x00A5;&nbsp;U+00A5,
            &#x20AC;&nbsp;U+20AC,  &#x2116;&nbsp;U+2116,  &#xFF04;&nbsp;U+FF04,
            &#xFFE1;&nbsp;U+FFE1,  &#xFFE5;&nbsp;U+FFE5
        </ul>
    </ul>

    <p class="note">In CSS3 no distinction is made among the levels of
      strictness in non-CJK text: only CJK codepoints are affected, unless
      the text is marked as Chinese or Japanese, in which case some additional
      common codepoints are affected. However a future level of CSS may add
      behaviors affecting non-CJK text.

    <p>Support for this property is <em>optional</em>. It is recommended
      for UAs that wish to support CJK typography and strongly recommended
      for UAs in the Japanese market.</p>

    <p class="note">The CSSWG recognizes that in a future edition of the
      specification finer control over line breaking may be necessary to
      satisfy high-end publishing requirements.

  <h3 id="word-break">
    Word Breaking Rules: the 'word-break' property</h3>

    <table class="propdef">
      <tbody>
        <tr>
          <th>Name:</th>
          <td><dfn>word-break</dfn></td>
        </tr>
        <tr>
          <th>Value:</th>
          <td>normal | keep-all | break-all</td>
        </tr>
        <tr>
          <th>Initial:</th>
          <td>normal</td>
        </tr>
        <tr>
          <th>Applies to:</th>
          <td>all elements</td>
        </tr>
        <tr>
          <th>Inherited:</th>
          <td>yes</td>
        </tr>
        <tr>
          <th>Percentages:</th>
          <td>N/A</td>
        </tr>
        <tr>
          <th>Media:</th>
          <td>visual</td>
        </tr>
        <tr>
          <th>Computed&#160;value:</th>
          <td>specified value</td>
        </tr>
      </tbody>
    </table>

    <p>This property specifies line break opportunities within words.
      Values have the following meanings:</p>

    <dl>
      <dt><dfn title="word-break:normal">''normal''</dfn></dt>
      <dd>Break lines according to their usual rules.</dd>
      <dt><dfn title="word-break:break-all">''break-all''</dfn></dt>
      <dd>Lines may break between any two characters within words.