[css-text] Make tab-size accept <<number>> so that it is animatable. Also account for 'letter-spacing' and 'word-spacing'. <https://www.w3.org/mid/CADhPm3u95z0_xB8eRsmv=EGgb8+8yXDEnw-EAVp3eqrGjs9ykQ@mail.gmail.com>

Author: fantasai

css-text/Overview.bs

@@ -716,17 +716,19 @@ Languages and Typesetting</h4>
 
     <pre class="propdef">
     Name: tab-size
-    Value: <<integer>> | <<length>>
+    Value: <<number>> | <<length>>
     Initial: 8
     Applies to: block containers
     Inherited: yes
     Computed value: the specified integer or length made absolute
-    Animation type: <a href="https://drafts.csswg.org/css-transitions-1/#animtype-length">length</a>
+    Animation type: <a href="http://www.w3.org/TR/css-transitions-1/#animtype-length">length</a>,
+    <a href="http://www.w3.org/TR/css-transitions-1/#animtype-number">number</a>, or calc
     Canonical order: n/a
     </pre>
 
     <p>This property determines the tab size used to render preserved tab characters (U+0009).
-      Integers represent the measure as multiples of the space character's advance width (U+0020).
+      A <<number>> represents the measure as a multiple of the space character's advance width (U+0020)
+      plus the associated 'letter-spacing' and 'word-spacing'.
       Negative values are not allowed.
 
 <h2 id="line-breaking">
@@ -2321,6 +2323,8 @@ Changes</h2>
   2013 CSS3 Text <abbr title="Last Call Working Draft">LCWD</abbr></a></h3>
 
   <ul>
+    <li>Switched 'tab-size' to use <<number>> so that it is animatable,
+        and defined it to also account for 'letter-spacing' and 'word-spacing'.
     <li>Made 'text-align' a shorthand of 'text-align-last' and the new 'text-align-all' property.
     <li>Removed dependence of 'text-align-last' on ''text-align: justify'',
         since the problem it solves is now solved by the shorthanding relationship.