[css3-fonts] revise @font-feature-values rule OM, add in description of how font-size-adjust affects relative unit sizes

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-11-june-2013>Editor's Draft 11
-    June 2013</h2>
+   <h2 class="no-num no-toc" id=editors-draft-5-july-2013>Editor's Draft 5
+    July 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-20130611/">http://www.w3.org/TR/2013/ED-css3-fonts-20130611/</a> -->
+     <!-- <dd><a href="http://www.w3.org/TR/2013/ED-css3-fonts-20130705/">http://www.w3.org/TR/2013/ED-css3-fonts-20130705/</a> -->
 
 
     <dt>Latest version:
@@ -1653,13 +1653,6 @@ <h3 id=font-size-adjust-prop><span class=secno>3.6 </span>Relative sizing:
    id=aspect-value>aspect value</dfn></a>. Precisely defined, it is equal to
    the x-height of a font divided by the font size.
 
-  <p class=issue>How does the use of ‘<a
-   href="#propdef-font-size-adjust"><code
-   class=property>font-size-adjust</code></a>’ affect <a
-   href="http://www.w3.org/TR/css3-values/#font-relative-lengths"><em>font-relative</em></a>
-   unit sizes? Are all units affected the same way, i.e. including the
-   definition of ‘<code class=property>em</code>’?
-
   <p>In situations where font fallback occurs, fallback fonts may not share
    the same aspect ratio as the desired font family and will thus appear less
    readable. The font-size-adjust property is a way to preserve the
@@ -1699,9 +1692,10 @@ <h3 id=font-size-adjust-prop><span class=secno>3.6 </span>Relative sizing:
    <p class=caption>Text with and without the use of font-size-adjust
   </div>
 
-  <p>This property allows authors to specify an aspect value for an element
-   that will effectively preserve the x-height of the first choice font,
-   whether it is substituted or not. Values have the following meanings:
+  <p>This property allows authors to specify an <a
+   href="#aspect-value"><i>aspect value</i></a> for an element that will
+   effectively preserve the x-height of the first choice font, whether it is
+   substituted or not. Values have the following meanings:
 
   <dl>
    <dt><dfn id=font-size-adjust-none-value
@@ -1712,10 +1706,10 @@ <h3 id=font-size-adjust-prop><span class=secno>3.6 </span>Relative sizing:
    <dt><dfn id=font-size-adjust-auto-value
     title="auto!!font-size-adjust">auto</dfn>
 
-   <dd>Behaves just like &lt;number>, except the number used is the aspect
-    value calculated by user agents for the first font in the list of fonts
-    defined for the initial value of the <a href="#propdef-font-family"
-    title="font-family!!property">‘<code
+   <dd>Behaves just like &lt;number>, except the number used is the <a
+    href="#aspect-value"><i>aspect value</i></a> calculated by user agents
+    for the first font in the list of fonts defined for the initial value of
+    the <a href="#propdef-font-family" title="font-family!!property">‘<code
     class=property>font-family</code>’</a> property. Effectively this is
     the default font used when <a href="#propdef-font-family"
     title="font-family!!property">‘<code
@@ -1726,39 +1720,48 @@ <h3 id=font-size-adjust-prop><span class=secno>3.6 </span>Relative sizing:
 
    <dt><dfn id=aspect-ratio-value><var>&lt;number&gt;</var></dfn>
 
-   <dd>Specifies the aspect value used in the calculation below to calculate
-    the adjusted font size:
+   <dd>Specifies the <a href="#aspect-value"><i>aspect value</i></a> used in
+    the calculation below to calculate the adjusted font size:
     <pre>c  =  ( a / a' ) s
 </pre>
 
     <p>where:</p>
 
     <pre>s  =  font-size value
-a  =  aspect value as specified by the font-size-adjust property
-a' =  aspect value of actual font
+a  =  <a href="#aspect-value"><i>aspect value</i></a> as specified by the font-size-adjust property
+a' =  <a href="#aspect-value"><i>aspect value</i></a> of actual font
 c  =  adjusted font-size to use
 </pre>
 
     <p>This value applies to any font that is selected but in typical usage
-     it should be based on the aspect value of the first font in the
-     font-family list. If this is specified accurately, the <tt>(a/a')</tt>
-     term in the formula above is effectively 1 for the first font and no
-     adjustment occurs. If the value is specified inaccurately, text rendered
-     using the first font in the family list will display differently in
-     older user agents that don't support font-size-adjust.</p>
+     it should be based on the <a href="#aspect-value"><i>aspect
+     value</i></a> of the first font in the font-family list. If this is
+     specified accurately, the <tt>(a/a')</tt> term in the formula above is
+     effectively 1 for the first font and no adjustment occurs. If the value
+     is specified inaccurately, text rendered using the first font in the
+     family list will display differently in older user agents that don't
+     support font-size-adjust.</p>
   </dl>
 
-  <p>Authors can calculate the aspect value for a given font by comparing
-   spans with the same content but different font-size-adjust properties. If
-   the same font-size is used, the spans will match when the font-size-adjust
-   value is accurate for the given font.
+  <p>The value of ‘<a href="#propdef-font-size-adjust"><code
+   class=property>font-size-adjust</code></a>’ affects the size of relative
+   units that are based on font metrics of the <a
+   href="#first-available-font"><i>first available font</i></a> such as
+   <code>ex</code> and <code>ch</code> but does not affect the size of
+   <code>em</code> units.
+
+  <p>Authors can calculate the <a href="#aspect-value"><i>aspect
+   value</i></a> for a given font by comparing spans with the same content
+   but different font-size-adjust properties. If the same font-size is used,
+   the spans will match when the font-size-adjust value is accurate for the
+   given font.
 
   <div class=example>
-   <p>Two spans with borders are used to determine the aspect value of a
-    font. The font-size is the same for both spans but the font-size-adjust
-    property is specified only for the right span. Starting with a value of
-    0.5, the aspect value can be adjusted until the borders around the two
-    letters line up.</p>
+   <p>Two spans with borders are used to determine the <a
+    href="#aspect-value"><i>aspect value</i></a> of a font. The font-size is
+    the same for both spans but the font-size-adjust property is specified
+    only for the right span. Starting with a value of 0.5, the aspect value
+    can be adjusted until the borders around the two letters line up.</p>
 
    <pre>p {
     font-family: Futura;
@@ -1776,14 +1779,15 @@ <h3 id=font-size-adjust-prop><span class=secno>3.6 </span>Relative sizing:
 &lt;p>&lt;span>b&lt;/span>&lt;span class="adjust">b&lt;/span>&lt;/p>
 </pre>
 
-   <div class=figure><img alt="Futura with an aspect value of 0.5"
+   <div class=figure><img alt="Futura with an <i>aspect value</i> of 0.5"
     src=beforefontsizeadjust.png>
-    <p class=caption>Futura with an aspect value of 0.5
+    <p class=caption>Futura with an <a href="#aspect-value"><i>aspect
+     value</i></a> of 0.5
    </div>
 
    <p>The box on the right is a bit bigger than the one on the left, so the
-    aspect value of this font is something less than 0.5. Adjust the value
-    until the boxes align.</p>
+    <a href="#aspect-value"><i>aspect value</i></a> of this font is something
+    less than 0.5. Adjust the value until the boxes align.</p>
   </div>
   <!-- prop: font -->
 
@@ -3051,11 +3055,11 @@ <h4 id=default-same-origin-restriction><span class=secno>4.9.1
    definitions considered cross origin must not be loaded:
 
   <pre>
-/* same origin (i.e. domain, protocol, port match document) */
+/* same origin (i.e. domain, scheme, port match document) */
 src: url(fonts/simple.ttf);
 src: url(//fonts/simple.ttf);
 
-/* cross origin, different protocol */
+/* cross origin, different scheme */
 src: url(https://example.com/fonts/simple.ttf);
 
 /* cross origin, different domain */
@@ -3069,34 +3073,16 @@ <h4 id=allowing-cross-origin-font-loading><span class=secno>4.9.2
    using cross-site origin controls <a href="#CORS"
    rel=biblioentry>[CORS]<!--{{!CORS}}--></a> for fonts loaded via HTTP.
    Sites can explicitly allow cross-site downloading of font data using the
-   <code>Access-Control-Allow-Origin</code> HTTP header. For other protocols,
+   <code>Access-Control-Allow-Origin</code> HTTP header. For other schemes,
    no explicit relaxation mechanism is defined or required.
 
-  <p>For font loads over HTTP, cross-origin requests must be made with the
-   following parameter settings which are used in conjunction with the <a
-   href="http://www.w3.org/TR/cors/#cross-origin-request-0"> <em>cross-origin
-   request algorithm</em></a> <a href="#CORS"
-   rel=biblioentry>[CORS]<!--{{!CORS}}--></a>:
-
-  <ul>
-   <li><em>request URL</em> — the URL of the font resource in the <a
-    href="#descdef-src"><code>src</code></a> descriptor
-
-   <li><em>request method</em> — GET
-
-   <li><em>author request headers</em> — none
-
-   <li><em>request entity body</em> — empty
-
-   <li><em>source origin</em> — the origin of the page which linked to the
-    stylesheet
-
-   <li><em>manual redirect flag</em> — false
-
-   <li><em>omit credentials flag</em> — true
-
-   <li><em>force preflight flag</em> — false
-  </ul>
+  <p>For font loads, user agents must use the <a
+   href="http://www.w3.org/TR/html5/infrastructure.html#cors-enabled-fetch">potentially
+   CORS-enabled fetch</a> method defined by the <a href="#HTML5"
+   rel=biblioentry>[HTML5]<!--{{!HTML5}}--></a> specification for URL's
+   defined within @font-face rules. When fetching, user agents must use
+   "Anonymous" mode, set the referrer source to the stylesheet's URL and set
+   the origin to the URL of the containing document.
 
   <h2 id=font-matching-algorithm><span class=secno>5 </span>Font Matching
    Algorithm</h2>
@@ -5779,25 +5765,61 @@ <h3 id=om-fontfeaturevalues><span class=secno>8.2 </span>The <a
    rule.
 
   <pre class=idl>interface CSSFontFeatureValuesRule : CSSRule {
-  readonly attribute DOMString familyList;
-  readonly attribute DOMString valueText;
-};</pre>
+  attribute DOMString fontFamily;
+  readonly attribute CSSFontFeatureValuesMap annotation;
+  readonly attribute CSSFontFeatureValuesMap ornaments;
+  readonly attribute CSSFontFeatureValuesMap stylistic;
+  readonly attribute CSSFontFeatureValuesMap swash;
+  readonly attribute CSSFontFeatureValuesMap characterVariant;
+  readonly attribute CSSFontFeatureValuesMap styleset;
+}
+
+[MapClass(DOMString, sequence&lt;unsigned long&gt;)]
+interface CSSFontFeatureValuesMap {
+  void set(DOMString featureValueName, sequence&lt;unsigned long&gt; values);
+}</pre>
 
   <dl class=idl-attributes>
-   <dt><var>familyList</var> of type <code>DOMString</code>, readonly
+   <dt><var>fontFamily</var> of type <code>DOMString</code>
 
    <dd>The list of one or more font families for which a given set of feature
     values is defined.
 
-   <dt><var>valueText</var> of type <code>DOMString</code>, readonly
+   <dt>value maps of type <code>CSSFontFeatureValuesMap</code>, readonly
 
-   <dd>Serialized set of feature values.
+   <dd>Maps of feature values associated with feature value names for a given
+    ‘<a href="#propdef-font-variant-alternates"><code
+    class=property>font-variant-alternates</code></a>’ value type
   </dl>
 
-  <p class=issue>This needs to be reworked along the lines of <a
-   href="http://lists.w3.org/Archives/Public/www-style/2013May/0781.html">Tab's
-   proposal</a> for a rule containing a family list and map objects for each
-   of the feature types.
+  <p>Each value map attribute of <a
+   href="#cssfontfeaturevaluesrule"><code>CSSFontFeatureValuesRule</code></a>
+   reflects the values defined via a corresponding <a
+   href="#featurevalueblock"><i title="feature_value_block">feature value
+   block</i></a>. Thus, the <var title="annotation
+   attribute">annotation</var> attribute contains the values contained within
+   a <code title="@annotation">@annotation</code> <a
+   href="#featurevalueblock"><i title="feature_value_block">feature value
+   block</i></a>, the <var title="ornaments attribute">ornaments</var>
+   attribute contains the values contained with a <code
+   title="@ornaments">@ornaments</code> <a href="#featurevalueblock"><i
+   title="feature_value_block">feature value block</i></a> and so forth.
+
+  <p>The <code>CSSFontFeatureValuesMap</code> interface inherits the
+   <code>clear</code>, <code>delete</code>, <code>get</code>, and
+   <code>has</code> methods from <code>MapClass</code>. The <code>set</code>
+   method takes an array of unsigned integers and associates it with a given
+   <code>featureValueName</code>. The method behaves the same as the
+   inherited method in <code>MapClass</code> but if the associated <a
+   href="#featurevalueblock"><i title="feature_value_block">feature value
+   block</i></a> only allows a limited number of values, the <code>set</code>
+   method throws an <code>InvalidAccessError</code> exception when the input
+   array to <code>set</code> contains more than the limited number of values.
+   See the description of <a
+   href="#multi-valued-feature-value-definitions">multi-valued feature value
+   definitions</a> for details on the maximum number of values allowed for a
+   given type of <a href="#featurevalueblock"><i
+   title="feature_value_block">feature value block</i></a>.
 
   <h2 class=no-num id=platform-props-to-css>Appendix A: Mapping platform font
    properties to CSS properties</h2>
@@ -5896,12 +5918,17 @@ <h3 class=no-num id=recent-changes> Changes from the <a
     href="#at-font-feature-values-rule"><code>@font-feature-values</code></a>
     rules
 
-   <li>Tightened definition of synthetic oblique
-
    <li>Revised definition of ‘<a href="#descdef-unicode-range"><code
     class=property>unicode-range</code></a>’ descriptor
 
    <li>Detailed font matching of composite faces
+
+   <li>Revised object model interface of CSSFontFeatureValuesRule
+
+   <li>Detailed effect of ‘<a href="#propdef-font-size-adjust"><code
+    class=property>font-size-adjust</code></a>’ on relative unit sizes
+
+   <li>Reference the potentially CORS-enabled fetch method defined in HTML5
   </ul>
 
   <h2 class=no-num id=acknowledgments>Acknowledgments</h2>