Clarifications to letter-spacing and word-spacing

--HG--
extra : rebase_source : 85a8e59a7ec95c2f7f1944bd2238b9ff8c3eddbc

Author: fantasai

css3-text/Overview.html

@@ -32,14 +32,14 @@
 
    <h1>CSS Text Level 3</h1>
 
-   <h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 19 July 2012</h2>
+   <h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 31 July 2012</h2>
 
    <dl>
     <dt>This version:
 
     <dd><a href="http://dev.w3.org/csswg/css3-text/">$Date$ (CVS
      $Revision$)</a> <!--
-    <dd><a href="http://www.w3.org/TR/2012/WD-css3-text-20120719/">http://www.w3.org/TR/2012/WD-css3-text-20120719/</a></dd>
+    <dd><a href="http://www.w3.org/TR/2012/WD-css3-text-20120731/">http://www.w3.org/TR/2012/WD-css3-text-20120731/</a></dd>
   -->
 
 
@@ -1199,8 +1199,8 @@ <h3 id=line-break-details><span class=secno>5.1. </span> Line Breaking
 
    <li>For <a href="#soft-wrap-opportunity"><i>soft wrap
     opportunities</i></a> created by characters that disappear at the line
-    break (i.e. spaces), properties on the element containing that character
-    control the line breaking at that opportunity. For <a
+    break (e.g. U+0020 SPACE), properties on the element containing that
+    character control the line breaking at that opportunity. For <a
     href="#soft-wrap-opportunity"><i>soft wrap opportunities</i></a> defined
     by the boundary between two characters, the properties on the element
     containing the boundary control breaking.
@@ -2571,15 +2571,15 @@ <h2 id=spacing><span class=secno>8. </span> Spacing</h2>
    <pre>p { word-spacing: -50% 0%; }</pre>
   </div>
 
-  <p id=spacing-limit>The <dfn
-   id=ltspacing-limitgt>&lt;spacing-limit&gt;</dfn> value type, which
+  <p id=spacing-limits>The <dfn
+   id=ltspacing-limitsgt>&lt;spacing-limits&gt;</dfn> value type, which
    represents optimum, minimum, and maximum spacing in ‘<a
    href="#word-spacing0"><code class=property>word-spacing</code></a>’ and
    ‘<a href="#letter-spacing0"><code
    class=property>letter-spacing</code></a>’, is defined as
 
   <pre class=prod><dfn
-   id=ltspacing-limit>&lt;spacing-limit></dfn> = [ normal | &lt;length&gt; | &lt;percentage&gt;]{1,3}</pre>
+   id=ltspacing-limits>&lt;spacing-limits></dfn> = [ normal | &lt;length&gt; | &lt;percentage&gt;]{1,3}</pre>
 
   <p>If three values are specified, they represent the optimum, minimum, and
    maximum in that order. If only two values are specified, then the first
@@ -2588,54 +2588,51 @@ <h2 id=spacing><span class=secno>8. </span> Spacing</h2>
    minimum, and maximum. The values are interpreted as defined below:
 
   <dl>
-   <dt><dfn id=normal3 title="&lt;spacing-limit&gt;:normal">‘<code
+   <dt><dfn id=normal3 title="&lt;spacing-limits&gt;:normal">‘<code
     class=css>normal</code>’</dfn>
 
-   <dd>Specifies the normal optimum/minimum/maximum spacing, as defined by
-    the current font and/or the user agent. See <a
-    href="#normal-spacing">below</a>.
+   <dd>Specifies normal spacing as defined by the current font and/or the
+    user agent; see <a href="#normal-spacing">below</a>. A ‘<code
+    class=css>normal</code>’ optimum spacing value computes to zero.
 
    <dt><dfn id=ltlengthgt
-    title="&lt;spacing-limit&gt;:&lt;length&gt;">‘<code
+    title="&lt;spacing-limits&gt;:&lt;length&gt;">‘<code
     class=css>&lt;length&gt;</code>’</dfn>
 
-   <dd>Specifies extra spacing <em>in addition to</em> the normal optimum
-    spacing. Values may be negative, but there may be
-    implementation-dependent limits.
+   <dd>Specifies extra spacing <em>in addition to</em> the intrinsic
+    inter-character/inter-word spacing defined by the font. Values may be
+    negative, but there may be implementation-dependent limits.
 
    <dt><dfn id=ltpercentagegt
-    title="&lt;spacing-limit&gt;:&lt;percentage&gt;">‘<code
+    title="&lt;spacing-limits&gt;:&lt;percentage&gt;">‘<code
     class=css>&lt;percentage&gt;</code>’</dfn>
 
    <dd>Specifies the additional spacing as a percentage of the affected
-    character. Only valid on ‘<a href="#word-spacing0"><code
-    class=property>word-spacing</code></a>’. Negative values are not
-    allowed.
+    character's <i>advance measure</i>. Only valid on ‘<a
+    href="#word-spacing0"><code class=property>word-spacing</code></a>’.
   </dl>
 
   <p>In the absence of justification the optimum spacing is be used. The text
    justification process may alter the spacing from its optimum (see the <a
    href="#text-justify">‘<code class=property>text-justify</code>’</a>
    property, above) but must not violate the minimum spacing limit and should
-   also avoid exceeding the maximum.
+   also avoid exceeding the maximum. The UA may also use the difference
+   between the minimum/maximum limits and the optimum as input into a
+   weighting algorithm for justification.
 
   <p>The minimum is treated as a hard constraint: if the maximum is less than
    the minimum, then the used it is set to the minimum. Likewise for the
    optimum. Similarly if the maximum is less than the optimum, then the used
    optimum is set to the used maximum.
 
   <p><dfn id=normal-spacing>Normal spacing</dfn>: Although ‘<code
-   class=css>normal</code>’ spacing is UA-defined, the normal minimum and
-   maximum must be defined relative to the optimum so that the minimum and
-   maximum limits increase and decrease with changes to the optimum spacing.
-   These limits may also vary according to some measure of the amount of text
-   on a line (e.g. block width divided by font size), as larger measures can
-   accommodate tighter spacing constraints. Normal optimum/minimum/maximum
-   spacing may also vary based on the value of the <a
+   class=css>normal</code>’ minimum and maximum spacing limits are
+   UA-defined, they must be defined relative to the optimum so that the
+   limits increase and decrease with changes to the optimum spacing. Normal
+   limits may also vary according to the value of the <a
    href="#text-justify">‘<code class=property>text-justify</code>’</a>
-   property, the element's language, and other factors. Normal spacing
-   between a pair of <a href="#connected-scripts">connected</a> or <a
-   href="#cursive-scripts">cursive</a> characters is always zero.
+   property, the element's language, some measure of the amount of text on a
+   line (e.g. block width divided by font size), and/or other factors.
 
   <h3 id=word-spacing><span class=secno>8.1. </span> Word Spacing: the ‘<a
    href="#word-spacing0"><code class=property>word-spacing</code></a>’
@@ -2651,7 +2648,7 @@ <h3 id=word-spacing><span class=secno>8.1. </span> Word Spacing: the ‘<a
     <tr>
      <th><a href="#values">Value</a>:
 
-     <td><a href="#spacing-limit">&lt;spacing-limit&gt;</a>
+     <td><a href="#spacing-limits">&lt;spacing-limits&gt;</a>
 
     <tr>
      <th>Initial:
@@ -2681,8 +2678,9 @@ <h3 id=word-spacing><span class=secno>8.1. </span> Word Spacing: the ‘<a
     <tr>
      <th>Computed value:
 
-     <td>as specified, except with &lt;length> values computed to absolute
-      lengths
+     <td>an optimum, minimum, and maximum value, each consisting of either an
+      absolute length, a percentage, or the keyword ‘<code
+      class=css>normal</code>’
   </table>
 
   <p>This property specifies the minimum, maximum, and optimal spacing
@@ -2691,7 +2689,7 @@ <h3 id=word-spacing><span class=secno>8.1. </span> Word Spacing: the ‘<a
   <p>Additional spacing is applied to each word-separator character left in
    the text after the <a href="#white-space-rules">white space processing
    rules</a> have been applied, and should be applied half on each side of
-   the character.
+   the character unless otherwise dictated by typographic tradition.
 
   <div class=example>
    <p>The following example will make all the spaces between words in Arabic
@@ -2732,7 +2730,7 @@ <h3 id=letter-spacing><span class=secno>8.2. </span> Tracking: the ‘<a
     <tr>
      <th><a href="#values">Value</a>:
 
-     <td><a href="#spacing-limit">&lt;spacing-limit&gt;</a>
+     <td><a href="#spacing-limits">&lt;spacing-limits&gt;</a>
 
     <tr>
      <th>Initial:
@@ -2762,14 +2760,14 @@ <h3 id=letter-spacing><span class=secno>8.2. </span> Tracking: the ‘<a
     <tr>
      <th>Computed value:
 
-     <td>as specified, except with &lt;length> values computed to absolute
-      lengths
+     <td>an optimum, minimum, and maximum value, each consisting of either an
+      absolute length, a percentage, or the keyword ‘<code
+      class=css>normal</code>’
   </table>
 
   <p>This property specifies the minimum, maximum, and optimal spacing
    between <a href="#character"><i>characters</i></a>. Letter-spacing is
-   applied in addition to any word-spacing. ‘<code
-   class=css>normal</code>’ optimum letter-spacing is typically zero.
+   applied in addition to any word-spacing.
 
   <p>Letter-spacing must not be applied at the beginning or at the end of a
    line. At element boundaries, the total letter spacing between two
@@ -2811,8 +2809,8 @@ <h3 id=letter-spacing><span class=secno>8.2. </span> Tracking: the ‘<a
    class=property>letter-spacing</code></a>’ applied to
    <code>A&amp;zwsp;B</code> is identical to <code>AB</code>.
 
-  <p>When the resulting space between two characters is not the same as the
-   default space, user agents should not use optional ligatures.
+  <p>When the effective letter-spacing between two characters is not zero,
+   user agents should not apply optional ligatures.
 
   <h2 id=edge-effects><span class=secno>9. </span> Edge Effects</h2>
 
@@ -5228,7 +5226,7 @@ <h2 class=no-num id=appendix-h-full-property-index>Appendix H: Full
     <tr>
      <th><a class=property href="#letter-spacing0">letter-spacing</a>
 
-     <td>&lt;spacing-limit&gt;
+     <td>&lt;spacing-limits&gt;
 
      <td>normal
 
@@ -5571,7 +5569,7 @@ <h2 class=no-num id=appendix-h-full-property-index>Appendix H: Full
     <tr>
      <th><a class=property href="#word-spacing0">word-spacing</a>
 
-     <td>&lt;spacing-limit&gt;
+     <td>&lt;spacing-limits&gt;
 
      <td>normal
 

css3-text/Overview.src.html

@@ -791,7 +791,7 @@ <h3 id="line-break-details">
       or <i>soft wrap opportunity</i> in the flow.
     <li>The line breaking behavior of a replaced element
       is equivalent to that of the Object Replacement Character (U+FFFC).
-    <li>For <i>soft wrap opportunities</i> created by characters that disappear at the line break (i.e. spaces),
+    <li>For <i>soft wrap opportunities</i> created by characters that disappear at the line break (e.g. U+0020 SPACE),
       properties on the element containing that character control the line breaking at that opportunity.
       For <i>soft wrap opportunities</i> defined by the boundary between two characters,
       the properties on the element containing the boundary control breaking.
@@ -1889,10 +1889,10 @@ <h2 id="spacing">
     <pre>p { word-spacing: -50% 0%; }</pre>
   </div>
 
-  <p id="spacing-limit">The <dfn>&lt;spacing-limit&gt;</dfn> value type,
+  <p id="spacing-limits">The <dfn>&lt;spacing-limits&gt;</dfn> value type,
     which represents optimum, minimum, and maximum spacing in 'word-spacing'
     and 'letter-spacing', is defined as
-  <pre class="prod"><dfn>&lt;spacing-limit></dfn> = [ normal | &lt;length&gt; | &lt;percentage&gt;]{1,3}</pre>
+  <pre class="prod"><dfn>&lt;spacing-limits></dfn> = [ normal | &lt;length&gt; | &lt;percentage&gt;]{1,3}</pre>
 
   <p>If three values are specified, they represent the optimum, minimum,
     and maximum in that order.
@@ -1902,20 +1902,21 @@ <h2 id="spacing">
     minimum, and maximum. The values are interpreted as defined below:
 
   <dl>
-    <dt><dfn title="&lt;spacing-limit&gt;:normal">''normal''</dfn></dt>
-      <dd>Specifies the normal optimum/minimum/maximum spacing, as defined
-        by the current font and/or the user agent. See <a href="#normal-spacing">below</a>.
+    <dt><dfn title="&lt;spacing-limits&gt;:normal">''normal''</dfn></dt>
+      <dd>Specifies normal spacing
+        as defined by the current font and/or the user agent;
+        see <a href="#normal-spacing">below</a>.
+        A ''normal'' optimum spacing value computes to zero.
       </dd>
-    <dt><dfn title="&lt;spacing-limit&gt;:&lt;length&gt;">''&lt;length&gt;''</dfn>
-      <dd>Specifies extra spacing <em>in addition to</em> the normal optimum
-        spacing.
-        Values may be negative, but there may be implementation-dependent
-        limits.
+    <dt><dfn title="&lt;spacing-limits&gt;:&lt;length&gt;">''&lt;length&gt;''</dfn>
+      <dd>Specifies extra spacing <em>in addition to</em>
+        the intrinsic inter-character/inter-word spacing defined by the font.
+        Values may be negative, but there may be implementation-dependent limits.
       </dd>
-    <dt><dfn title="&lt;spacing-limit&gt;:&lt;percentage&gt;">''&lt;percentage&gt;''</dfn>
+    <dt><dfn title="&lt;spacing-limits&gt;:&lt;percentage&gt;">''&lt;percentage&gt;''</dfn>
       <dd>Specifies the additional spacing as a percentage of the affected
-        character.
-        Only valid on 'word-spacing'. Negative values are not allowed.
+        character's <i>advance measure</i>.
+        Only valid on 'word-spacing'.
       </dd>
   </dl>
 
@@ -1924,26 +1925,23 @@ <h2 id="spacing">
     from its optimum (see the <a href="#text-justify">'text-justify'</a>
     property, above) but must not violate the minimum spacing limit
     and should also avoid exceeding the maximum.
+    The UA may also use the difference between the minimum/maximum limits
+    and the optimum as input into a weighting algorithm for justification.
 
   <p>The minimum is treated as a hard constraint: if the maximum is less
     than the minimum, then the used it is set to the minimum. Likewise
     for the optimum. Similarly if the maximum is less than the optimum,
     then the used optimum is set to the used maximum.
 
    <p><dfn id="normal-spacing">Normal spacing</dfn>:
-    Although ''normal'' spacing is UA-defined, the normal minimum and
-    maximum must be defined relative to the optimum so that the minimum
-    and maximum limits increase and decrease with changes to the optimum spacing.
-    These limits may also vary according to some measure of the amount
-    of text on a line (e.g. block width divided by font size), as
-    larger measures can accommodate tighter spacing constraints.
-    Normal optimum/minimum/maximum spacing may also vary based on the
-    value of the <a href="#text-justify">'text-justify'</a> property,
-    the element's language, and other factors.
-    Normal spacing between a pair of
-    <a href="#connected-scripts">connected</a> or
-    <a href="#cursive-scripts">cursive</a>
-    characters is always zero.
+    Although ''normal'' minimum and maximum spacing limits are UA-defined,
+    they must be defined relative to the optimum so that the limits
+    increase and decrease with changes to the optimum spacing.
+    Normal limits may also vary according to
+    the value of the <a href="#text-justify">'text-justify'</a> property,
+    the element's language,
+    some measure of the amount of text on a line (e.g. block width divided by font size),
+    and/or other factors.
 
   <h3 id="word-spacing">
     Word Spacing: the 'word-spacing' property</h3>
@@ -1956,7 +1954,7 @@ <h3 id="word-spacing">
         </tr>
         <tr>
           <th><a href="#values">Value</a>:
-          <td><a href="#spacing-limit">&lt;spacing-limit&gt;</a>
+          <td><a href="#spacing-limits">&lt;spacing-limits&gt;</a>
           </td>
         </tr>
         <tr>
@@ -1981,7 +1979,8 @@ <h3 id="word-spacing">
         </tr>
         <tr>
           <th>Computed&#160;value:</th>
-          <td>as specified, except with &lt;length> values computed to absolute lengths</td>
+          <td>an optimum, minimum, and maximum value,
+            each consisting of either an absolute length, a percentage, or the keyword ''normal''
         </tr>
       </tbody>
     </table>
@@ -1992,7 +1991,8 @@ <h3 id="word-spacing">
     <p>Additional spacing is applied to each word-separator character
       left in the text after the <a href="#white-space-rules">white space
       processing rules</a> have been applied, and should be applied half on
-      each side of the character.
+      each side of the character
+      unless otherwise dictated by typographic tradition.
 
     <div class="example">
       <p>The following example will make all the spaces between words in Arabic
@@ -2030,7 +2030,7 @@ <h3 id="letter-spacing">
         </tr>
         <tr>
           <th><a href="#values">Value</a>:
-          <td><a href="#spacing-limit">&lt;spacing-limit&gt;</a>
+          <td><a href="#spacing-limits">&lt;spacing-limits&gt;</a>
           </td>
         </tr>
         <tr>
@@ -2055,15 +2055,15 @@ <h3 id="letter-spacing">
         </tr>
         <tr>
           <th>Computed&#160;value:</th>
-          <td>as specified, except with &lt;length> values computed to absolute lengths
+          <td>an optimum, minimum, and maximum value,
+            each consisting of either an absolute length, a percentage, or the keyword ''normal''
         </tr>
       </tbody>
     </table>
 
     <p>This property specifies the minimum, maximum, and optimal spacing
-      between <i>characters</i>. Letter-spacing is applied in
-      addition to any word-spacing. ''normal'' optimum letter-spacing is
-      typically zero.</p>
+      between <i>characters</i>.
+      Letter-spacing is applied in addition to any word-spacing.
 
     <p>Letter-spacing must not be applied at the beginning or at the end
        of a line. At element boundaries, the total letter spacing between
@@ -2104,8 +2104,8 @@ <h3 id="letter-spacing">
       Unicode Cf category). For example, 'letter-spacing' applied to
       <code>A&amp;zwsp;B</code> is identical to <code>AB</code>.
 
-    <p>When the resulting space between two characters is not the same as the
-      default space, user agents should not use optional ligatures.</p>
+    <p>When the effective letter-spacing between two characters is not zero,
+      user agents should not apply optional ligatures.</p>
 
 <h2 id="edge-effects">
   Edge Effects</h2>