[css3-writing-modes] Improvements to character orientation rules; clarify that appendix B only covers HTML4

--HG--
extra : rebase_source : e377348fa5d075b0a6fe89549e18ee913f9ce44b

Author: fantasai

css3-writing-modes/Overview.html

@@ -357,7 +357,8 @@ <h2 class="no-num no-toc" id=Contents> Table of Contents</h2>
    <li class=no-num><a href="#character-properties">Appendix A. Characters
     and Properties</a>
 
-   <li class=no-num><a href="#bidi-html"> Appendix B: Bidi Rules for HTML</a>
+   <li class=no-num><a href="#bidi-html"> Appendix B: Bidi Rules for HTML
+    4</a>
 
    <li class=no-num><a href="#script-orientations">Appendix C: Vertical
     Scripts in Unicode</a>
@@ -1931,17 +1932,21 @@ <h3 id=text-orientation><span class=secno>5.1. </span> Orienting Text: the
   <h4 id=vertical-orientations><span class=secno>5.1.1. </span> Mixed
    Vertical Orientations</h4>
 
-  <p> <a href="#UTR50" rel=biblioentry>[UTR50]<!--{{!UTR50}}--></a> defines
-   the "mixed vertical orientation" (MVO) property in UCD format <a
-   href="#UAX44" rel=biblioentry>[UAX44]<!--{{!UAX44}}--></a>. When ‘<a
-   href="#text-orientation0"><code
+  <p> <a href="#UTR50" rel=biblioentry>[UTR50]<!--{{!UTR50}}--></a> defines a
+   property for the default character orientation of mixed-orientation
+   vertical text. When ‘<a href="#text-orientation0"><code
    class=property>text-orientation</code></a>’ is ‘<a
    href="#mixed-right"><code class=css>mixed-right</code></a>’, the UA must
-   render a <a href="#character"><i>character</i></a> upright if the MVO
-   value is ‘<code class=css>U</code>’, ‘<code class=css>T</code>’,
-   ‘<code class=css>Tu</code>’, or ‘<code class=css>Tr</code>’, or
-   else sideways (90° clockwise from horizontal) if ‘<code
-   class=css>R</code>’.
+   render a <a href="#character"><i>character</i></a> upright if its
+   orientation property is <code>U</code>, <code>T</code>, or
+   <code>Tu</code>; or <a href="#typeset-sideways">typeset it sideways</a>
+   (90° clockwise from horizontal) if its orientation property is
+   <code>R</code>. For <code>Tr</code> <a
+   href="#character"><i>characters</i></a>, which are intended to be either
+   transformed or rotated sideways, the UA may assume that appropriate glyphs
+   for upright typesetting are given in the font and render them upright;
+   alternately it may check for such glyphs first, and fall back to
+   typesetting them sideways if the appropriate glyphs are missing.
 
   <p class=issue> As of the time of publication, Unicode has not yet
    officially updated its orientation data to account for the many errata
@@ -1969,15 +1974,6 @@ <h4 id=vertical-font-features><span class=secno>5.1.2. </span> Vertical
     class=css>vert</code>’ feature must be enabled.) Furthermore,
     characters from horizontal cursive scripts (such as Arabic) are shaped in
     their isolated forms when typeset upright.
-    <p class=note> Note that in OpenType systems, <a
-     href="#character"><i>characters</i></a> from the Mongolian and Phags-pa
-     scripts must actually be rendered <a
-     href="#typeset-sideways">sideways</a>. This is because the "upright"
-     orientation in the Unicode code charts (which assume vertical
-     typesetting) and the "upright" orientation of the glyphs of these
-     scripts in most OpenType fonts (which assume horizontal typesetting)
-     don't match.
-
     <p class=note>Note that even when typeset "upright", some glyphs should
      appear rotated. For example, dashes and enclosing punctuation (such as
      〈 LEFT ANGLE BRACKET U+3008) should be oriented relative to the inline
@@ -1993,6 +1989,16 @@ <h4 id=vertical-font-features><span class=secno>5.1.2. </span> Vertical
      revisions of <a href="#UTR50"
      rel=biblioentry>[UTR50]<!--{{!UTR50}}--></a>.
 
+    <p> In some font systems (e.g. OpenType), to correctly render a <a
+     href="#character"><i>character</i></a> belonging to the Mongolian or
+     Phags-pa script upright, the UA must actually typeset it <a
+     href="#typeset-sideways">sideways</a>.
+
+    <p class=note>This is because the "upright" orientation in the Unicode
+     code charts (which assume vertical typesetting) and the "upright"
+     orientation of the glyphs of these scripts in most OpenType fonts (which
+     assume horizontal typesetting) don't match.
+
    <dt id=typeset-sideways>sideways characters
 
    <dd> Are typeset with horizontal metrics, and vertical typesetting
@@ -2013,6 +2019,13 @@ <h4 id=vertical-font-features><span class=secno>5.1.2. </span> Vertical
    glyph variations, and any other features meant for text typeset in
    vertical lines are <em>not</em> used.
 
+  <p class=note> The OpenType ‘<code class=css>vrt2</code>’ feature,
+   which is intended for mixed-orientation typesetting, is not used by CSS.
+   It delegates the responsibility for orienting glyphs to the font designer.
+   CSS instead dictates the orientation through <a href="#UTR50"
+   rel=biblioentry>[UTR50]<!--{{!UTR50}}--></a> and orients glyphs by
+   typesetting them sideways or upright as appropriate.
+
   <p class=issue>This section needs additional work. Suggestions are welcome.
    <!-- random notes
   Property to customize text-orientation (and line breaking class) of various
@@ -3755,7 +3768,7 @@ <h2 class=no-num id=character-properties>Appendix A. Characters and
     from the first combining character in the sequence.
   </ul>
 
-  <h2 class=no-num id=bidi-html> Appendix B: Bidi Rules for HTML</h2>
+  <h2 class=no-num id=bidi-html> Appendix B: Bidi Rules for HTML 4</h2>
 
   <p>The style sheet rules that would achieve the bidi behaviors specified in
    <a href="#HTML401" rel=biblioentry>[HTML401]<!--{{HTML401}}--></a> for the

css3-writing-modes/Overview.src.html

@@ -1354,10 +1354,18 @@ <h4 id='vertical-orientations'>
 Mixed Vertical Orientations</h4>
 
   <p>
-    [[!UTR50]] defines the "mixed vertical orientation" (MVO) property in UCD format [[!UAX44]].
+    [[!UTR50]] defines a property for the default character orientation of mixed-orientation vertical text.
     When 'text-orientation' is ''mixed-right'',
-    the UA must render a <i>character</i> upright if the MVO value is ''U'', ''T'', ''Tu'', or ''Tr'',
-    or else sideways (90&deg; clockwise from horizontal) if ''R''.
+    the UA must render a <i>character</i> upright if its orientation property is
+    <code>U</code>, <code>T</code>, or <code>Tu</code>;
+    or <a href="#typeset-sideways">typeset it sideways</a> (90&deg; clockwise from horizontal)
+    if its orientation property is <code>R</code>.
+    For <code>Tr</code> <i>characters</i>,
+    which are intended to be either transformed or rotated sideways,
+    the UA may assume that appropriate glyphs for upright typesetting
+    are given in the font and render them upright;
+    alternately it may check for such glyphs first,
+    and fall back to typesetting them sideways if the appropriate glyphs are missing.
 
   <p class='issue'>
     As of the time of publication,
@@ -1383,13 +1391,6 @@ <h4 id='vertical-font-features'>
       (E.g. the OpenType ''vert'' feature must be enabled.)
       Furthermore, characters from horizontal cursive scripts (such as Arabic)
       are shaped in their isolated forms when typeset upright.
-      <p class="note">
-        Note that in OpenType systems,
-        <i>characters</i> from the Mongolian and Phags-pa scripts
-        must actually be rendered <a href="#typeset-sideways">sideways</a>.
-        This is because the "upright" orientation in the Unicode code charts (which assume vertical typesetting)
-        and the "upright" orientation of the glyphs of these scripts in most OpenType fonts (which assume horizontal typesetting)
-        don't match.
       <p class="note">Note that even when typeset "upright",
         some glyphs should appear rotated.
         For example, dashes and enclosing punctuation 
@@ -1402,6 +1403,15 @@ <h4 id='vertical-font-features'>
         Unicode published draft data on which <i>characters</i> should appear sideways
         as the SVO property in <a href="http://www.unicode.org/reports/tr50/tr50-6.Orientation.txt">this data file</a>;
         however, this property has been abandoned for future revisions of [[!UTR50]].
+      <p>
+        In some font systems (e.g. OpenType),
+        to correctly render a <i>character</i> belonging to the Mongolian or Phags-pa script upright,
+        the UA must actually typeset it <a href="#typeset-sideways">sideways</a>.
+      <p class="note">This is because the "upright" orientation
+        in the Unicode code charts (which assume vertical typesetting)
+        and the "upright" orientation of the glyphs of these scripts
+        in most OpenType fonts (which assume horizontal typesetting)
+        don't match.
 
     <dt id='typeset-sideways'>sideways characters 
     <dd>
@@ -1423,6 +1433,13 @@ <h4 id='vertical-font-features'>
     Vertical metrics, vertical glyph variations, and any other features meant
     for text typeset in vertical lines are <em>not</em> used.
 
+  <p class="note">
+    The OpenType ''vrt2'' feature, which is intended for mixed-orientation typesetting,
+    is not used by CSS.
+    It delegates the responsibility for orienting glyphs to the font designer.
+    CSS instead dictates the orientation through [[!UTR50]]
+    and orients glyphs by typesetting them sideways or upright as appropriate.
+
   <p class=issue>This section needs additional work. Suggestions are welcome.
 
 <!-- random notes
@@ -2879,7 +2896,7 @@ <h2 id="character-properties" class="no-num">Appendix A.
   </ul>
 
 <h2 id="bidi-html" class=no-num>
-Appendix B: Bidi Rules for HTML</h2>
+Appendix B: Bidi Rules for HTML 4</h2>
 
 <p>The style sheet rules that would achieve the bidi behaviors specified
 in [[HTML401]] for the HTML Strict doctype are given below: