[css-fonts] first pass on revised description of unicode-range descriptor

Author: John Daggett

css-fonts/Fonts.html

@@ -112,15 +112,15 @@
 
    <h1>CSS Fonts Module Level 3</h1>
 
-   <h2 class="no-num no-toc" id=editors-draft-20-may-2013>Editor's Draft 20
+   <h2 class="no-num no-toc" id=editors-draft-21-may-2013>Editor's Draft 21
     May 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-20130520/">http://www.w3.org/TR/2013/ED-css3-fonts-20130520/</a> -->
+     <!-- <dd><a href="http://www.w3.org/TR/2013/ED-css3-fonts-20130521/">http://www.w3.org/TR/2013/ED-css3-fonts-20130521/</a> -->
 
 
     <dt>Latest version:
@@ -2332,10 +2332,10 @@ <h3 id=src-desc><span class=secno>4.3 </span>Font reference: the <a
 
   <p>The name can optionally be enclosed in quotes. For OpenType and TrueType
    fonts, this string is used to match only the Postscript name or the full
-   font name in the name table of locally available fonts. Which is used
-   varies by platform and font, so authors should include both of these names
-   to assure proper matching across platforms. Platform substitutions for a
-   given font name must not be used.
+   font name in the name table of locally available fonts. Which type of name
+   is used varies by platform and font, so authors should include both of
+   these names to assure proper matching across platforms. Platform
+   substitutions for a given font name must not be used.
 
   <pre>
 /* bold face of Gentium */
@@ -2510,7 +2510,7 @@ <h3 id=font-prop-desc><span class=secno>4.4 </span>Font property
    properties except that relative keywords are not allowed, ‘<code
    class=property>bolder</code>’ and ‘<code
    class=property>lighter</code>’. If these descriptors are omitted,
-   default values are assumed.
+   initial values are assumed.
 
   <p>The value for these font face style attributes is used in place of the
    style implied by the underlying font data. This allows authors to combine
@@ -2533,66 +2533,128 @@ <h3 id=unicode-range-desc><span class=secno>4.5 </span>Character range: the
     <tr>
      <td>Value:
 
-     <td>&lt;urange>#
+     <td><dfn id=lturange>&lt;urange></dfn>#
 
     <tr>
      <td><em>Initial:</em>
 
      <td>U+0-10FFFF
   </table>
 
-  <p>This descriptor defines the range of Unicode characters supported by a
-   given font. The values of <span class=index-def id=lturangegt
-   title="&lt;urange&gt;"><a name=value-def-urange>&lt;urange&gt;</a></span>
-   are expressed using hexadecimal numbers prefixed by "U+" or "u+",
-   corresponding to <a href="http://www.unicode.org/charts/">Unicode
-   character code points</a>. The unicode-range descriptor serves as a hint
-   for user agents when deciding whether or not to download a font resource.
+  <p>This descriptor defines the set of Unicode codepoints that may be
+   supported by the font face for which it is declared. The descriptor value
+   is a comma-delimited list of Unicode range (<dfn id=lturangegt
+   title=value-def-urange><code>&lt;urange&gt;</code></dfn>) values. The
+   union of these ranges defines the set of codepoints that serves as a hint
+   for user agents when deciding whether or not to download a font resource
+   for a given text run.
 
-  <p>Unicode range values are written using hexadecimal values and are ASCII
-   case-insensitive. Each is prefixed by "U+" or "u+" and multiple,
-   discontinuous ranges are separated by commas. Whitespace before or after
-   commas is ignored. Valid character code values vary between 0 and 10FFFF
-   inclusive. A single range has three basic forms:
+  <p>Each <code>&lt;urange&gt;</code> value is a <a
+   href="#descdef-unicode-range"><code>UNICODE-RANGE</code></a> token made up
+   of a "U+" or "u+" prefix followed by a codepoint range in one of the three
+   forms listed below. Ranges that do not fit one of the these three forms
+   are considered to be parse errors and the descriptor is omitted.
 
   <ul>
    <li>a single code point (e.g. U+416)
 
-   <li>an interval value range (e.g. U+400-4ff)
+   <li>an interval value range defined by two hyphen-separated codepoints
+    that indicate the inclusive start and end codepoints of a range (e.g.
+    U+400-4ff)
 
-   <li>a range where trailing ‘<code class=css>?</code>’ characters imply
-    ‘<code class=css>any digit value</code>’ (e.g. U+4??)
+   <li>a wildcard value range where trailing ‘<code class=css>?</code>’
+    characters imply ‘<code class=css>any digit value</code>’ (e.g.
+    U+4??)
   </ul>
 
-  <p>Ranges that do not fit any of the above three forms are considered to be
-   parse errors and the descriptor is omitted. Interval ranges consisting of
-   a single code point are valid. Ranges specified with ‘?’ that lack an
-   initial digit (e.g. "U+???") are also valid, and are treated as if there
-   was a single 0 before the question marks (thus, "U+???" = "U+0???" =
-   "U+0000-0FFF"). "U+??????" is not a syntax error, even though "U+0??????"
-   would be. Ranges can overlap but interval ranges that descend (e.g.
-   U+400-32f) are invalid and omitted rather than treated as parse errors;
-   they have no effect on other ranges in a list of ranges. Ranges are
-   clipped to the domain of Unicode code points (currently 0 – 10FFFF
-   inclusive); a range entirely outside the domain is omitted. Without any
-   valid ranges, the descriptor is omitted. User agents may normalize the
-   list of ranges into a list that is different but represents the same set
-   of character code points.
-
-  <p>The character range can be a subset of the full <a
-   href="#character-map"><em>character map</em></a> of the underlying font.
-   The effective unicode-range used when mapping characters to fonts is the
-   intersection of the unicode range specified and the underlying <a
-   href="#character-map"><em>character map</em></a> of the font. This means
-   that authors do not need to define the unicode-range of a font precisely,
-   broad ranges for which a sparse set of code points are defined in the font
-   can be used. Code points outside of the defined unicode-range are ignored,
-   regardless of whether the font contains a glyph for that code point or
-   not. User agents that download fonts for characters outside the defined
-   unicode-range are considered non-conformant. Likewise, user agents that
-   render a character using a font resource for which the defined
-   unicode-range does not include that character are also considered
-   non-conformant.
+  <p>Individual codepoints are written using hexadecimal values that
+   correspond to <a href="http://www.unicode.org/charts/">Unicode character
+   codepoints</a>. Valid character code values vary between 0 and 10FFFF
+   inclusive. They are ASCII case-insensitive.
+
+  <p>For interval ranges, the start and end codepoints must be valid Unicode
+   values and the end codepoint must be greater than or equal to the start
+   codepoint. Wildcard ranges specified with ‘?’ that lack an initial
+   digit (e.g. "U+???") are valid and treated as if there was a single 0
+   before the question marks (thus, "U+???" = "U+0???" = "U+0000-0FFF").
+   "U+??????" is not a syntax error, even though "U+0??????" would be.
+   Wildcard ranges that extend beyond the end of valid codepoint values are
+   clipped to the range of valid codepoint values. Ranges that do not conform
+   to these restrictions are considered parse errors and the descriptor is
+   omitted.
+
+  <p>Within the comma-delimited list of Unicode ranges in a ‘<a
+   href="#descdef-unicode-range"><code
+   class=property>unicode-range</code></a>’ descriptor declaration, ranges
+   may overlap. Whitespace before or after commas is ignored. The union of
+   these ranges defines the set of codepoints for which the corresponding
+   font may be used. User agents must not download or use the font for
+   codepoints outside this set. User agents may normalize the list of ranges
+   into a list that is different but represents the same set of codepoints.
+
+  <p>The associated font may not contain glyphs for the entire set of
+   codepoints defined by the ‘<a href="#descdef-unicode-range"><code
+   class=property>unicode-range</code></a>’ descriptor. When the font is
+   used the effective character map is the intersection of the codepoints
+   defined by ‘<a href="#descdef-unicode-range"><code
+   class=property>unicode-range</code></a>’ with the font's character map.
+   This allows authors to define supported ranges in terms of broad ranges
+   without worrying about the precise codepoint ranges supported by the
+   underlying font.</p>
+  <!--
+<p>This descriptor defines the range of Unicode characters supported by
+a given font.  The values of <span class="index-def"
+title="&lt;urange&gt;"><a
+name="value-def-urange">&lt;urange&gt;</a></span> are expressed using
+hexadecimal numbers prefixed by "U+" or "u+", corresponding to <a
+href="http://www.unicode.org/charts/">Unicode character code points</a>.
+The unicode-range descriptor serves as a hint for user agents when
+deciding whether or not to download a font resource.</p>
+
+<p>Unicode range values are written using hexadecimal values and are ASCII
+case-insensitive.  Each is prefixed by "U+" or "u+" and multiple, discontinuous
+ranges are separated by commas.  Whitespace before or after commas is
+ignored.  Valid character code values vary between 0 and 10FFFF
+inclusive.  A single range has three basic forms:
+</p>
+
+<ul>
+  <li>a single code point (e.g. U+416)</li>
+  <li>an interval value range (e.g. U+400-4ff)</li>
+  <li>a range where trailing '?' characters imply 'any digit value' (e.g. U+4??)</li>
+</ul>
+
+<p>Ranges that do not fit any of the above three forms are considered to
+be parse errors and the descriptor is omitted. Interval ranges
+consisting of a single code point are valid. Ranges specified with ‘?’
+that lack an initial digit (e.g. "U+???") are also valid, and are
+treated as if there was a single 0 before the question marks (thus,
+"U+???" = "U+0???" = "U+0000-0FFF"). "U+??????" is not a syntax error,
+even though "U+0??????" would be. Ranges can overlap but interval ranges
+that descend (e.g. U+400-32f) are invalid and omitted rather than
+treated as parse errors; they have no effect on other ranges in a list
+of ranges. Ranges are clipped to the domain of Unicode code points
+(currently 0 – 10FFFF inclusive); a range entirely outside the domain is
+omitted. Without any valid ranges, the descriptor is omitted. User
+agents may normalize the list of ranges into a list that is different
+but represents the same set of character code points.
+</p>
+
+<p>The character range can be a subset of the full <em>character map</em> of the
+underlying font.  The effective unicode-range used when mapping
+characters to fonts is the intersection of the unicode range specified
+and the underlying <em>character map</em> of the font.  This means that authors
+do not need to define the unicode-range of a font precisely, broad
+ranges for which a sparse set of code points are defined in the font can
+be used.  Code points outside of the defined unicode-range are ignored,
+regardless of whether the font contains a glyph for that code point or
+not.  User agents that download fonts for characters outside the defined
+unicode-range are considered non-conformant.  Likewise, user agents that
+render a character using a font resource for which the defined
+unicode-range does not include that character are also considered
+non-conformant.
+</p>
+-->
 
   <p>Example ranges for specific languages or characters:
 
@@ -2799,7 +2861,7 @@ <h3 id=font-rend-desc><span class=secno>4.6 </span>Font features: the <a
      <td>normal
   </table>
 
-  <p>These descriptors define default settings that apply when the font
+  <p>These descriptors define initial settings that apply when the font
    defined by an <code>@font-face</code> rule is rendered. They do not affect
    font selection. Values are identical to those defined for the
    corresponding ‘<a href="#propdef-font-variant"><code
@@ -5861,8 +5923,8 @@ <h2 class=no-num id=index>Index</h2>
    <li>&lt;relative-size&gt;, <a href="#ltrelative-sizegt"
     title="&lt;relative-size&gt;"><strong>3.5</strong></a>
 
-   <li>&lt;urange&gt;, <a href="#lturangegt"
-    title="&lt;urange&gt;"><strong>4.5</strong></a>
+   <li>&lt;urange>, <a href="#lturange"
+    title="&lt;urange>"><strong>4.5</strong></a>
 
    <li>@font-face, <a href="#font-face" title="@font-face">4.1</a>, <a
     href="#font-face0" title="@font-face">4.3</a>
@@ -6119,6 +6181,9 @@ <h2 class=no-num id=index>Index</h2>
    <li>unicode-range, <a href="#descdef-unicode-range"
     title=unicode-range><strong>4.5</strong></a>
 
+   <li>value-def-urange, <a href="#lturangegt"
+    title=value-def-urange><strong>4.5</strong></a>
+
    <li>weight, <a href="#weight" title=weight><strong>2</strong></a>
 
    <li>width, <a href="#width" title=width><strong>2</strong></a>