Clarifications to baseline alignment

Author: fantasai

css3-writing-modes/Overview.html

@@ -206,10 +206,6 @@ <h2 class="no-num no-toc" id=Contents> Table of Contents</h2>
      <li><a href="#text-orientation"><span class=secno>5.1. </span> Orienting
       Text: the &lsquo;<code class=property>text-orientation</code>&rsquo;
       property</a>
-      <ul class=toc>
-       <li><a href="#vertical-typesetting"><span class=secno>5.1.1. </span>
-        Vertical Typesetting</a>
-      </ul>
     </ul>
 
    <li><a href="#abstract-box"><span class=secno>6. </span> Abstract Box
@@ -286,15 +282,15 @@ <h2 class="no-num no-toc" id=Contents> Table of Contents</h2>
    <li class=no-num><a href="#bidi-html"> Appendix A: Bidi Rules for HTML</a>
 
 
+   <li class=no-num><a href="#character-properties">Appendix Q Characters and
+    Properties</a>
+
    <li class=no-num><a href="#script-orientations">Appendix B:
     Bi-orientational Transformations</a>
 
    <li class=no-num><a href="#vertical-typesetting-details">Appendix C:
     Vertical Typesetting Synthesis</a>
 
-   <li class=no-num><a href="#character-properties">Appendix Q Characters and
-    Properties</a>
-
    <li class=no-num><a href="#intrinsic-sizing">Appendix D: Intrinsic
     Dimensions</a>
     <ul class=toc>
@@ -1355,18 +1351,30 @@ <h3 id=replaced-baselines><span class=secno>4.3. </span> Atomic Inline
 
   <h3 id=baseline-alignment><span class=secno>4.4. </span> Baseline Alignment</h3>
 
-  <p>The dominant baseline is used in CSS for alignment in two cases:
+  <p>The <dfn id=dominant-baseline>dominant baseline</dfn> (which <a
+   href="#text-baselines">can change</a> based on the writing mode) is used
+   in CSS for alignment in two cases:
 
   <ul>
-   <li>Aligning glyphs from different fonts within the same inline box. The
-    glyphs are aligned by matching up the positions of the dominant baseline.
-    
-
-   <li>Aligning a child inline within its parent. The child is aligned to the
-    parent by matching the parent's dominant baseline to the same baseline in
-    the child. (E.g. if the parent's dominant baseline is alphabetic, then
-    the child's alphabetic baseline is matched to the parent's alphabetic
-    baseline, even if the child's dominant baseline is something else.)
+   <li><strong>Aligning glyphs from different fonts within the same inline
+    box.</strong> The glyphs are aligned by matching up the positions of the
+    dominant baseline in their corresponding fonts.
+
+   <li><strong>Aligning a child inline-level box within its parent.</strong>
+    For the &lsquo;<code class=property>vertical-align</code>&rsquo; value of
+    &lsquo;<a href="#baseline"><code class=css>baseline</code></a>&rsquo;,
+    child is aligned to the parent by matching the parent's dominant baseline
+    to the same baseline in the child. (E.g. if the parent's dominant
+    baseline is alphabetic, then the child's alphabetic baseline is matched
+    to the parent's alphabetic baseline, even if the child's dominant
+    baseline is something else.) For values of &lsquo;<code
+    class=css>sub</code>&rsquo;, &lsquo;<code class=css>super</code>&rsquo;,
+    &lsquo;<code class=css>&lt;length&gt;</code>&rsquo;, and &lsquo;<code
+    class=css>&lt;percentage&gt;</code>&rsquo;, the baselines are aligned as
+    for &lsquo;<a href="#baseline"><code
+    class=css>baseline</code></a>&rsquo;, but the child is shifted according
+    to the offset given by its &lsquo;<code
+    class=property>vertical-align</code>&rsquo; value.
     <div class=example>
      <p>Given following sample markup:
 
@@ -1387,16 +1395,6 @@ <h3 id=baseline-alignment><span class=secno>4.4. </span> Baseline Alignment</h3>
      </div>
     </div>
 
-    <p>Baseline alignment in this fashion is used with the following values
-     of &lsquo;<code class=property>vertical-align</code>&rsquo;: &lsquo;<a
-     href="#baseline"><code class=css>baseline</code></a>&rsquo;,
-     &lsquo;<code class=css>sub</code>&rsquo;, &lsquo;<code
-     class=css>super</code>&rsquo;, &lt;length&gt;, &lt;percentage&gt;. In
-     the latter cases, the baselines are aligned as for &lsquo;<a
-     href="#baseline"><code class=css>baseline</code></a>&rsquo;, but the
-     child is shifted according to the offset given by its &lsquo;<code
-     class=property>vertical-align</code>&rsquo; value.
-
     <div class=example>
      <p>If we assign &lsquo;<code class=css>vertical-align:
       super</code>&rsquo; to the <code>.inner</code> element from the example
@@ -1551,15 +1549,10 @@ <h3 id=text-orientation><span class=secno>5.1. </span> Orienting Text: the
    sets the orientation of the line. Current values only have an effect in
    vertical writing modes.
 
-  <p id=grapheme-cluster>In this section only, the term <dfn
-   id=character>character</dfn> is defined as <em>extended grapheme
-   cluster</em> per <a href="#UAX29"
-   rel=biblioentry>[UAX29]<!--{{!UAX29}}--></a>. It is roughly equivalent to
-   what a language user considers to be a character or a basic unit of the
-   script (which might not be a single Unicode codepoint). The UA may further
-   tailor the definition as allowed by Unicode. See <a
-   href="#character-properties">Character Properties</a> for detailed
-   information on determing character properties.
+  <p>For readability, the term <a href="#character"><i>character</i></a> is
+   used in place of <em>extended grapheme cluster</em> in this section. See
+   <a href="#character-properties">Characters and Properties</a> for further
+   details.
 
   <p>Values have the following meanings:
 
@@ -1615,11 +1608,15 @@ <h3 id=text-orientation><span class=secno>5.1. </span> Orienting Text: the
 
     <p>If set on a non-replaced inline whose parent is not &lsquo;<a
      href="#sideways-left"><code class=css>sideways-left</code></a>&rsquo;,
-     this forces &lsquo;<a href="#isolate"><code
-     class=css>isolate</code></a>&rsquo; to be added to the computed value of
-     &lsquo;<a href="#unicode-bidi0"><code
-     class=property>unicode-bidi</code></a>&rsquo;. Layout of text is exactly
-     as for &lsquo;<a href="#sideways-right"><code
+     this forces bidi isolation: the &lsquo;<a href="#normal"><code
+     class=css>normal</code></a>&rsquo; and &lsquo;<a href="#embed"><code
+     class=css>embed</code></a>&rsquo; values of &lsquo;<a
+     href="#unicode-bidi0"><code
+     class=property>unicode-bidi</code></a>&rsquo; compute to &lsquo;<a
+     href="#isolate"><code class=css>isolate</code></a>&rsquo;, and &lsquo;<a
+     href="#bidi-override"><code class=css>bidi-override</code></a>&rsquo;
+     computes to &lsquo;<code class=css>bidi-override isolate</code>&rsquo;.
+     Layout of text is exactly as for &lsquo;<a href="#sideways-right"><code
      class=css>sideways-right</code></a>&rsquo; except that the text content
      and baseline table of each of the element's inline boxes is mirrored
      around a vertical axis along the center of its content box. The
@@ -1633,7 +1630,7 @@ <h3 id=text-orientation><span class=secno>5.1. </span> Orienting Text: the
      class=property>text-orientation</code></a>&rsquo; value other than
      &lsquo;<a href="#sideways-left"><code
      class=css>sideways-left</code></a>&rsquo;, an analogous transformation
-     is applied.
+     (and bidi isolation) is applied.
 
    <dt><dfn id=sideways>sideways</dfn>
 
@@ -1683,6 +1680,26 @@ <h3 id=text-orientation><span class=secno>5.1. </span> Orienting Text: the
     and sideways-right (writing-mode is vertical-rl)</p>
   </div>
 
+  <p>The orientation of characters belonging to the Common, Inherited, and
+   Unknown script categories may be UA- or font-dependent in vertical
+   typographic modes:
+
+  <ul>
+   <li>
+    <p>If the font and font system support mixed-orientation typesetting
+     (e.g. the OpenType font used has the <code>vrt2</code>), the UA should
+     rely on that feature to set &lsquo;<a href="#vertical-right"><code
+     class=css>vertical-right</code></a>&rsquo; text. Similarly if the font
+     and font system support upright typesetting (e.g. the OpenType font used
+     has the <code>vert</code> feature) then the UA should rely on that
+     feature to set &lsquo;<a href="#upright"><code
+     class=css>upright</code></a>&rsquo; text.
+
+   <li>
+    <p>If the UA needs to synthesize such features, then the settings in <a
+     href="#vertical-typesetting-details">Appendix C</a> are recommended.
+  </ul>
+
   <div class=example>
    <p>In the following example, the root element of a horizontal-only
     document is set to use &lsquo;<a href="#sideways"><code
@@ -1701,39 +1718,6 @@ <h3 id=text-orientation><span class=secno>5.1. </span> Orienting Text: the
     </pre>
   </div>
 
-  <h4 id=vertical-typesetting><span class=secno>5.1.1. </span> Vertical
-   Typesetting</h4>
-
-  <p>In vertical typographic modes, any character belonging to a vertical
-   script <em>must</em> be set using its base character's intrinsic
-   orientation. (See <a href="#script-orientations">Appendix B</a>.)
-   Characters belonging to horizontal-only scripts must set sideways (for
-   &lsquo;<a href="#vertical-right"><code
-   class=css>vertical-right</code></a>&rsquo;) or set upright (for &lsquo;<a
-   href="#upright"><code class=css>upright</code></a>&rsquo;) depending on
-   the &lsquo;<a href="#text-orientation0"><code
-   class=property>text-orientation</code></a>&rsquo; property.
-
-  <p>The orientation of characters belonging to the Common, Inherited, and
-   Unknown script categories may be UA- or font-dependent in vertical
-   typographic modes:
-
-  <ul>
-   <li>
-    <p>If the font and font system support mixed-orientation typesetting, the
-     UA should rely on that feature to set &lsquo;<a
-     href="#vertical-right"><code class=css>vertical-right</code></a>&rsquo;
-     text. Similarly if the font and font system support upright typesetting
-     then the UA should rely on that feature to set &lsquo;<a
-     href="#upright"><code class=css>upright</code></a>&rsquo; text.
-
-   <li>
-    <p>If the UA needs to synthesize such features (e.g. if an OpenType font
-     has only the <code>vert</code> but not the <code>vrt2</code> feature),
-     then the settings in <a href="#vertical-typesetting-details">Appendix
-     C</a> are recommended.
-  </ul>
-
   <h2 id=abstract-box><span class=secno>6. </span> Abstract Box Terminology</h2>
 
   <p><a href="#CSS21" rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> defines
@@ -2967,6 +2951,56 @@ <h2 class=no-num id=bidi-html> Appendix A: Bidi Rules for HTML</h2>
 { unicode-bidi: isolate; }
   </pre>
 
+  <h2 class=no-num id=character-properties>Appendix Q Characters and
+   Properties</h2>
+
+  <p>Unicode defines three character-level properties that are referenced in
+   CSS Writing Modes:
+
+  <dl>
+   <dt><a href="http://www.unicode.org/reports/tr11/#Definitions">East Asian
+    width</a>
+
+   <dd>Defined in <a href="#UAX11"
+    rel=biblioentry>[UAX11]<!--{{!UAX11}}--></a> and given as the
+    East_Asian_Width property.
+
+   <dt><a
+    href="http://www.unicode.org/reports/tr44/#General_Category_Values">General
+    Category</a>
+
+   <dd>Defined in <a href="#UAX44"
+    rel=biblioentry>[UAX44]<!--{{!UAX44}}--></a> and given as the
+    General_Category property.
+
+   <dt><a href="http://www.unicode.org/reports/tr24/#Values">Script
+    property</a>
+
+   <dd>Defined in <a href="#UAX24"
+    rel=biblioentry>[UAX24]<!--{{!UAX24}}--></a> and given as the Script
+    property. (UAs should include any ScriptExtensions.txt assignments in
+    this mapping.)
+  </dl>
+
+  <p id=grapheme-cluster>In several sections (as noted), the term <dfn
+   id=character>character</dfn> is defined as <em>extended grapheme
+   cluster</em> per <a href="#UAX29"
+   rel=biblioentry>[UAX29]<!--{{!UAX29}}--></a>. It is roughly equivalent to
+   what a language user considers to be a character or a basic unit of the
+   script (which might not be a single Unicode codepoint). The UA may further
+   tailor this definition as allowed by Unicode.
+
+  <p>Unicode defines properties for characters, but for &lsquo;<a
+   href="#text-orientation0"><code
+   class=property>text-orientation</code></a>&rsquo; and <a
+   href=vertical-typesetting-details>Vertical Typesetting Synthesis</a>, it
+   is necessary to determine the properties of a grapheme cluster. For the
+   purposes of CSS Writing Modes, the properties of a grapheme cluster are
+   given by its base character&#8212;except in one case: grapheme clusters
+   formed with an Enclosing Mark (Me) of the Common script are considered to
+   be Other Symbols (So) in the Common script. They are assumed to have the
+   same Unicode properties as the Replacement Character U+FFFD.
+
   <h2 class=no-num id=script-orientations>Appendix B: Bi-orientational
    Transformations</h2>
 
@@ -3077,6 +3111,12 @@ <h2 class=no-num id=vertical-typesetting-details>Appendix C: Vertical
 
   <p><em>This appendix is non-normative.</em>
 
+  <p>This section defines an algorithm for automatic typesetting of vertical
+   text. For readability, the term <a href="#character"><i>character</i></a>
+   is used in place of <em>extended grapheme cluster</em> in this section.
+   See <a href="#character-properties">Characters and Properties</a> for
+   further details.
+
   <p class=issue>This section needs careful review.
 
   <p>When &lsquo;<a href="#text-orientation0"><code
@@ -3100,9 +3140,10 @@ <h2 class=no-num id=vertical-typesetting-details>Appendix C: Vertical
     settings if possible).
 
    <li>Set any other characters that are assigned to a script (i.e. do not
-    belong to the Common, Inherited, or Unknown scripts) <a
-    href="#vertical-typesetting">as required by &lsquo;<code
-    class=property>text-orientation</code>&rsquo;</a>.
+    belong to the Common, Inherited, or Unknown scripts) as required by
+    &lsquo;<a href="#text-orientation0"><code
+    class=property>text-orientation</code></a>&rsquo; and <a
+    href="#script-orientations">Appendix B</a>.
   </ol>
 
   <p>When &lsquo;<a href="#text-orientation0"><code
@@ -3174,47 +3215,6 @@ <h2 class=no-num id=vertical-typesetting-details>Appendix C: Vertical
    of these are present, the font is considered to have vertical font
    settings available.
 
-  <h2 class=no-num id=character-properties>Appendix Q Characters and
-   Properties</h2>
-
-  <p>Unicode only defines properties for characters, but in the definition of
-   &lsquo;<a href="#text-orientation0"><code
-   class=property>text-orientation</code></a>&rsquo; and in <a
-   href=vertical-typesetting-details>Vertical Typesetting Synthesis</a>, it
-   is necessary to determine the properties of a grapheme cluster. For the
-   purposes of CSS Writing Modes, the properties of a grapheme cluster are
-   given by its base character&#8212;except in one case: grapheme clusters
-   formed with an Enclosing Mark (Me) of the Common script are considered to
-   be Other Symbols (So) in the Common script having the same Unicode
-   properties as the Replacement Character U+FFFD.
-
-  <p>Unicode defines three properties that are referenced here:
-
-  <dl>
-   <dt><a href="http://www.unicode.org/reports/tr11/#Definitions">East Asian
-    width</a>
-
-   <dd>Defined in <a href="#UAX11"
-    rel=biblioentry>[UAX11]<!--{{UAX11}}--></a> and given as the
-    East_Asian_Width property.
-
-   <dt><a
-    href="http://www.unicode.org/reports/tr44/#General_Category_Values">General
-    Category</a>
-
-   <dd>Defined in <a href="#UAX44"
-    rel=biblioentry>[UAX44]<!--{{UAX44}}--></a> and given as the
-    General_Category property.
-
-   <dt><a href="http://www.unicode.org/reports/tr24/#Values">Script
-    property</a>
-
-   <dd>Defined in <a href="#UAX24"
-    rel=biblioentry>[UAX24]<!--{{UAX24}}--></a> and given as the Script
-    property. (UAs should include any ScriptExtensions.txt assignments in
-    this mapping.)
-  </dl>
-
   <h2 class=no-num id=intrinsic-sizing>Appendix D: Intrinsic Dimensions</h2>
 
   <p><em>This section is normative.</em>
@@ -3581,6 +3581,16 @@ <h3 class=no-num id=normative-references> Normative references</h3>
     </dd>
    <!---->
 
+   <dt id=UAX44>[UAX44]
+
+   <dd>Mark Davis; Ken Whistler. <a
+    href="http://www.unicode.org/reports/tr44/tr44-6.html"><cite>Unicode
+    Character Database.</cite></a> 8 October 2010. Unicode Standard Annex
+    #44. URL: <a
+    href="http://www.unicode.org/reports/tr44/tr44-6.html">http://www.unicode.org/reports/tr44/tr44-6.html</a>
+    </dd>
+   <!---->
+
    <dt id=UNICODE>[UNICODE]
 
    <dd>The Unicode Consortium. <a
@@ -3661,36 +3671,6 @@ <h3 class=no-num id=other-references> Other references</h3>
     </dd>
    <!---->
 
-   <dt id=UAX11>[UAX11]
-
-   <dd>Asmus Freytag. <a
-    href="http://www.unicode.org/unicode/reports/tr11/tr11-8.html"><cite>East
-    Asian Width.</cite></a> 23 March 2001. Unicode Standard Annex #11. URL:
-    <a
-    href="http://www.unicode.org/unicode/reports/tr11/tr11-8.html">http://www.unicode.org/unicode/reports/tr11/tr11-8.html</a>
-    </dd>
-   <!---->
-
-   <dt id=UAX24>[UAX24]
-
-   <dd>Mark Davis; Ken Whistler. <a
-    href="http://www.unicode.org/reports/tr24/"><cite>Unicode Script
-    Property.</cite></a> 27 September 2010. Unicode Standard Annex #24. URL:
-    <a
-    href="http://www.unicode.org/reports/tr24/">http://www.unicode.org/reports/tr24/</a>
-    </dd>
-   <!---->
-
-   <dt id=UAX44>[UAX44]
-
-   <dd>Mark Davis; Ken Whistler. <a
-    href="http://www.unicode.org/reports/tr44/tr44-6.html"><cite>Unicode
-    Character Database.</cite></a> 8 October 2010. Unicode Standard Annex
-    #44. URL: <a
-    href="http://www.unicode.org/reports/tr44/tr44-6.html">http://www.unicode.org/reports/tr44/tr44-6.html</a>
-    </dd>
-   <!---->
-
    <dt id=UTN22>[UTN22]
 
    <dd>Elika J. Etemad. <a href="http://unicode.org/notes/tn22/"><cite>Robust