[css3-fonts] character handling tweaks

Author: John Daggett

css-fonts/Fonts.html

@@ -115,15 +115,15 @@
 
    <h1>CSS Fonts Module Level 3</h1>
 
-   <h2 class="no-num no-toc" id=editors-draft-10-june-2013>Editor's Draft 10
+   <h2 class="no-num no-toc" id=editors-draft-11-june-2013>Editor's Draft 11
     June 2013</h2>
 
    <dl id=authors>
     <dt>This version:
 
     <dd><a
      href="http://dev.w3.org/csswg/css-fonts/">http://dev.w3.org/csswg/css-fonts/</a>
-     <!-- <dd><a href="http://www.w3.org/TR/2013/ED-css3-fonts-20130610/">http://www.w3.org/TR/2013/ED-css3-fonts-20130610/</a> -->
+     <!-- <dd><a href="http://www.w3.org/TR/2013/ED-css3-fonts-20130611/">http://www.w3.org/TR/2013/ED-css3-fonts-20130611/</a> -->
 
 
     <dt>Latest version:
@@ -3342,6 +3342,12 @@ <h3 id=font-style-matching><span class=secno>5.2 </span>Matching font
     Font</a>) or using the missing character glyph from a default font.
   </ol>
 
+  <p>Optimizations of this process are allowed provided that an
+   implementation behaves as if the algorithm had been followed exactly.
+   Matching occurs in a well-defined order to insure that the results are as
+   consistent as possible across user agents, given an identical set of
+   available fonts and rendering technology.
+
   <h3 id=cluster-matching><span class=secno>5.3 </span>Cluster matching</h3>
 
   <p>When text contains characters such as combining marks, ideally the base
@@ -3402,8 +3408,8 @@ <h3 id=cluster-matching><span class=secno>5.3 </span>Cluster matching</h3>
   <h3 id=char-handling-issues><span class=secno>5.4 </span>Character handling
    issues</h3>
 
-  <p>The procedure above is always performed on text runs containing Unicode
-   characters, documents using legacy encodings are assumed to have been
+  <p>CSS font matching is always performed on text runs containing Unicode
+   characters, so documents using legacy encodings are assumed to have been
    transcoded before matching fonts. For fonts containing <a
    href="#character-map"><em title="character map">character maps</em></a>
    for both legacy encodings and Unicode, the contents of the legacy encoding
@@ -3413,22 +3419,23 @@ <h3 id=char-handling-issues><span class=secno>5.4 </span>Character handling
   <p>The font matching process does not assume that text runs are in either
    normalized or denormalized form (see <a href="#CHARMOD-NORM"
    rel=biblioentry>[CHARMOD-NORM]<!--{{CHARMOD-NORM}}--></a> for more
-   details). Layout engines often convert base character plus combining
-   character sequences into precomposed characters if they exist. The font
-   matching algorithm outlined here supports both ways and fonts can
-   generally support either but variations can occur. Authors should always
+   details). Fonts may only support precomposed forms and not the decomposed
+   sequence of base character plus combining marks. Authors should always
    tailor their choice of fonts to their content, including whether that
    content contains normalized or denormalized character streams.
 
-  <p>If a given character is a Private-Use Area Unicode codepoint and none of
-   the fonts in the fontlist contain a glyph for that codepoint, user agents
-   must display some form of missing glyph symbol for that character rather
-   than attempting <a href="#system-font-fallback"><em>system font
-   fallback</em></a> for that codepoint. When matching the replacement
-   character U+FFFD, user agents may skip the font matching process and
-   immediately display some form of missing glyph symbol, they are not
-   required to display the glyph from the font that would be selected by the
-   font matching process.
+  <p>If a given character is a Private-Use Area Unicode codepoint, user
+   agents must only match font families named in the ‘<code
+   class=property>font-family</code>’ list that are not generic families.
+   If none of the families named in the ‘<code
+   class=property>font-family</code>’ list contain a glyph for that
+   codepoint, user agents must display some form of missing glyph symbol for
+   that character rather than attempting <a
+   href="#system-font-fallback"><em>system font fallback</em></a> for that
+   codepoint. When matching the replacement character U+FFFD, user agents may
+   skip the font matching process and immediately display some form of
+   missing glyph symbol, they are not required to display the glyph from the
+   font that would be selected by the font matching process.
 
   <p>In general, the fonts for a given family will all have the same or
    similar <a href="#character-map"><em title="character map">character
@@ -3437,12 +3444,6 @@ <h3 id=char-handling-issues><span class=secno>5.4 </span>Character handling
    title="character map">character maps</em></a>. However, authors are
    cautioned that the use of such families can lead to unexpected results.
 
-  <p>Optimizations of this process are allowed provided that an
-   implementation behaves as if the algorithm had been followed exactly.
-   Matching occurs in a well-defined order to insure that the results are as
-   consistent as possible across user agents, given an identical set of
-   available fonts and rendering technology.
-
   <h3 id=font-matching-changes><span class=secno>5.5 </span>Font matching
    changes since CSS 2.1</h3>
 
@@ -3478,8 +3479,8 @@ <h3 id=font-matching-examples><span class=secno>5.6 </span>Font matching
 *:lang(zh-tw) { font: 800 14pt/16.5pt &quot;Li Sung&quot;, serif; }
 </pre>
 
-   <p>This selects any element that has the given language - Japanese or
-    Traditional Chinese - and uses the appropriate font.
+   <p>This selects any element that has the given language — Japanese or
+    Traditional Chinese — and uses the appropriate font.
   </div>
 
   <h2 id=font-rend-props><span class=secno>6 </span>Font Feature Properties</h2>