tighten up the font-feature-settings syntax

Author: John Daggett

css3-fonts/Fonts.html

@@ -120,15 +120,15 @@
 
    <h1>CSS Fonts Module Level 3</h1>
 
-   <h2 class="no-num no-toc" id=editors-draft-28-february-2012>Editor's Draft
-    28 February 2012</h2>
+   <h2 class="no-num no-toc" id=editors-draft-20-april-2012>Editor's Draft 20
+    April 2012</h2>
 
    <dl id=authors>
     <dt>This version:
 
     <dd><a
      href="http://dev.w3.org/csswg/css3-fonts/">http://dev.w3.org/csswg/css3-fonts/</a>
-     <!-- <dd><a href="http://www.w3.org/TR/2012/ED-css3-fonts-20120228/">http://www.w3.org/TR/2012/ED-css3-fonts-20120228/</a> -->
+     <!-- <dd><a href="http://www.w3.org/TR/2012/ED-css3-fonts-20120420/">http://www.w3.org/TR/2012/ED-css3-fonts-20120420/</a> -->
 
 
     <dt>Latest version:
@@ -168,12 +168,12 @@ <h2 class="no-num no-toc" id=editors-draft-28-february-2012>Editor's Draft
    <!--begin-copyright-->
    <p class=copyright><a
     href="http://www.w3.org/Consortium/Legal/ipr-notice#Copyright"
-    rel=license>Copyright</a> © 2012 <a href="http://www.w3.org/"><acronym
-    title="World Wide Web Consortium">W3C</acronym></a><sup>®</sup> (<a
-    href="http://www.csail.mit.edu/"><acronym title="Massachusetts Institute
-    of Technology">MIT</acronym></a>, <a href="http://www.ercim.eu/"><acronym
+    rel=license>Copyright</a> © 2012 <a href="http://www.w3.org/"><abbr
+    title="World Wide Web Consortium">W3C</abbr></a><sup>®</sup> (<a
+    href="http://www.csail.mit.edu/"><abbr title="Massachusetts Institute of
+    Technology">MIT</abbr></a>, <a href="http://www.ercim.eu/"><abbr
     title="European Research Consortium for Informatics and
-    Mathematics">ERCIM</acronym></a>, <a
+    Mathematics">ERCIM</abbr></a>, <a
     href="http://www.keio.ac.jp/">Keio</a>), All Rights Reserved. W3C <a
     href="http://www.w3.org/Consortium/Legal/ipr-notice#Legal_Disclaimer">liability</a>,
     <a
@@ -4418,12 +4418,14 @@ <h3 id=font-feature-settings-prop><span class=secno>6.12 </span>Low-level
 
   <p>The &lt;string&gt; is a case-sensitive OpenType feature tag. For it to
    match an OpenType feature contained in a font, it must follow the syntax
-   rules for tags. As specified in the OpenType specification, feature tags
-   contain four characters. Tag strings longer than four characters must be
-   ignored, user agents must not use a feature tag created by truncating the
-   string to four characters. Feature tags need only match a feature tag
-   defined in the font, they are not limited to explicitly registered
-   OpenType features. Fonts defining custom feature tags should follow the <a
+   rules for these tags. As specified in the OpenType specification, feature
+   tags contain four ASCII characters. Tag strings longer or shorter than
+   four characters, or containing characters outside the U+20-7E codepoint
+   range are invalid. User agents must not use a feature tag created by
+   truncating or padding the string to four characters. Feature tags need
+   only match a feature tag defined in the font, they are not limited to
+   explicitly registered OpenType features. Fonts defining custom feature
+   tags should follow the <a
    href="http://www.microsoft.com/typography/otspec/featuretags.htm">tag name
    rules</a> defined in the OpenType specification <a
    href="#OPENTYPE-FEATURES"
@@ -4446,8 +4448,10 @@ <h3 id=font-feature-settings-prop><span class=secno>6.12 </span>Low-level
 font-feature-settings: 'c2sc';         /* c2sc=1 enable caps to small caps */
 font-feature-settings: "liga" off;     /* liga=0 no common ligatures */
 font-feature-settings: "tnum", 'hist'; /* tnum=1, hist=1 enable tabular numbers and historical forms */
-font-feature-settings: "palin" off;    /* good idea but invalid tagname, ignored */
+font-feature-settings: "tnum" "hist";  /* invalid, need a comma-delimited list */
+font-feature-settings: "palin" off;    /* good idea but invalid tagname */
 font-feature-settings: "PKRN";         /* PKRN=1 enable custom feature */
+font-feature-settings: dlig;           /* invalid, tag must be a string */
 </pre>
 
   <p>Authors should generally use ‘<a href="#propdef-font-variant"><code
@@ -4458,10 +4462,8 @@ <h3 id=font-feature-settings-prop><span class=secno>6.12 </span>Low-level
 
   <p>Although specifically defined for OpenType feature tags, feature tags
    for other modern font formats that support font features may be added in
-   the future.
-
-  <p class=issue>While the use of quotes distinguishes feature tags as
-   defined in an external resource, they still seem a bit clumsy.
+   the future. Where possible, features defined for other font formats should
+   attempt to follow the pattern of registered OpenType tags.
 
   <div class=example>
    <p>The Japanese text below will be rendered with half-width kana