Clean up @supports definition and define support better.

Author: dbaron

css3-conditional/Overview.html

@@ -17,13 +17,13 @@
 
    <h1>CSS Conditional Rules Module Level 3</h1>
 
-   <h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 13 June 2011</h2>
+   <h2 class="no-num no-toc" id=longstatus-date>Editor's Draft 14 June 2011</h2>
 
    <dl>
     <dt>This version:
 
-    <dd><a href="http://www.w3.org/TR/2011/ED-css3-conditional-20110613/">
-     http://www.w3.org/TR/2011/ED-css3-conditional-20110613</a>
+    <dd><a href="http://www.w3.org/TR/2011/ED-css3-conditional-20110614/">
+     http://www.w3.org/TR/2011/ED-css3-conditional-20110614</a>
 
     <dt>Latest version:
 
@@ -178,6 +178,13 @@ <h2 class="no-num no-toc" id=contents>Table of contents</h2>
 
    <li><a href="#at-supports"><span class=secno>6. </span>Feature queries:
     the &lsquo;<code class=css>@supports</code>&rsquo; rule</a>
+    <ul class=toc>
+     <li><a href="#support-definition"><span class=secno>6.1.
+      </span>Definition of support</a>
+
+     <li><a href="#partial-implementations"><span class=secno>6.2.
+      </span>Partial implementations</a>
+    </ul>
 
    <li><a href="#at-document"><span class=secno>7. </span>Document queries:
     the &lsquo;<code class=css>@document</code>&rsquo; rule</a>
@@ -562,45 +569,46 @@ <h2 id=at-supports><span class=secno>6. </span>Feature queries: the
   : '(' S* declaration ')' S*
   ;</pre>
 
-  <p>The rules for evaluating the condition in each of the above grammar
-   terms are:
+  <p>Each of these grammar terms is associated with a boolean result, as
+   follows:
 
   <dl>
    <dt>supports_condition
 
-   <dd> evaluate the single child term
+   <dd> The result is the result of the single child term.
 
    <dt>supports_negation
 
-   <dd> negate the result of evaluating the single child term
+   <dd> The result is the <em>negation</em> of the result of the
+    <code>supports_condition_in_parens</code> child term.
 
    <dt>supports_conjunction
 
-   <dd> true if all of the (non-&lsquo;<code class=css>and</code>&rsquo;)
-    child terms are true, otherwise false
+   <dd> The result is true if the result of <em>all</em> of the
+    <code>supports_condition_in_parens</code> child terms is true; otherwise
+    it is false.
 
    <dt>supports_disjunction
 
-   <dd> true if any of the (non-&lsquo;<code class=css>or</code>&rsquo;)
-    child terms are true, otherwise false
+   <dd> The result is true if the result of <em>any</em> of the
+    <code>supports_condition_in_parens</code> child terms is true; otherwise
+    it is false.
 
    <dt>supports_condition_in_parens
 
-   <dd> evaluate the single (non-&lsquo;<code class=css>(</code>&rsquo; and
-    non-&lsquo;<code class=css>)</code>&rsquo;) child term
+   <dd> The result is the result of the single
+    <code>supports_condition</code> or
+    <code>supports_declaration_condition</code> child term.
 
    <dt>supports_declaration_condition
 
-   <dd> true if the user agent supports the declaration (which is the same as
-    the rule for whether the user agent parses the declaration), otherwise
-    false <span class=issue>Need more normative prose here; probably some in
-    the snapshot which we (unfortunately) need to copy rather than
-    cite.</span>
+   <dd> The result is whether the CSS processor <a
+    href="#support-definition">supports</a> the declaration.
   </dl>
 
-  <p>and the condition of the &lsquo;<code class=css>@supports</code>&rsquo;
-   rule is the condition thus described for the <code>supports_rule</code>
-   term.
+  <p>The condition of the &lsquo;<code class=css>@supports</code>&rsquo; rule
+   is the result of the <code>supports_condition</code> term that is a child
+   of the <code>supports_rule</code> term.
 
   <div class=example>
    <p>For example, the following rule</p>
@@ -691,6 +699,41 @@ <h2 id=at-supports><span class=secno>6. </span>Feature queries: the
 }</pre>
   </div>
 
+  <h3 id=support-definition><span class=secno>6.1. </span>Definition of
+   support</h3>
+
+  <p>A CSS processor is considered to <dfn id=dfn-support>support</dfn> a
+   declaration (consisting of a property and value) if it implements the
+   given value of the given property.
+
+  <h3 id=partial-implementations><span class=secno>6.2. </span>Partial
+   implementations</h3>
+
+  <p>For forward-compatibility, <a
+   href="http://www.w3.org/TR/CSS21/syndata.html#declaration">section 4.1.8
+   (Declarations and properties)</a> of <a href="#CSS21"
+   rel=biblioentry>[CSS21]<!--{{!CSS21}}--></a> defines rules for handling
+   invalid properties and values. CSS processors that partially implement a
+   specification <strong>must</strong> treat any part of a value that they:
+
+  <ul>
+   <li>do not implement, or
+
+   <li>do not have a usable level of support for,
+  </ul>
+
+  <p>as invalid according to this rule, and <strong>must not</strong> accept
+   or support a declaration containing such a value. This allows authors to
+   use fallback (either in the <a href="#CSS1"
+   rel=biblioentry>[CSS1]<!--{{CSS1}}--></a> sense of declarations that are
+   overridden by later declarations or with the new capabilities provided by
+   the &lsquo;<code class=css>@supports</code>&rsquo; rule in this
+   specification) that works correctly for the features implemented. This
+   applies especially to compound values; implementations must implement all
+   parts of the value in order to consider the declaration supported, either
+   inside a ruleset or in the declaration condition of an &lsquo;<code
+   class=css>@supports</code>&rsquo; rule.
+
   <h2 id=at-document><span class=secno>7. </span>Document queries: the
    &lsquo;<code class=css>@document</code>&rsquo; rule</h2>
 
@@ -1174,6 +1217,9 @@ <h2 class=no-num id=index>Index</h2>
    <li>regexp(), <a href="#url-regexp"
     title="regexp()"><strong>7.</strong></a>
 
+   <li>support, <a href="#dfn-support"
+    title=support><strong>6.1.</strong></a>
+
    <li>&lsquo;<code class=css>@supports</code>&rsquo; rule, <a
     href="#supports-rule" title="'@supports' rule"><strong>6.</strong></a>
 

css3-conditional/Overview.src.html

@@ -388,46 +388,50 @@ <h2 id="at-supports">Feature queries: the '@supports' rule</h2>
   : '(' S* declaration ')' S*
   ;</pre>
 
-<p>The rules for evaluating the condition in each of the above grammar
-terms are:</p>
+<p>Each of these grammar terms is associated with a boolean result, as
+follows:</p>
 <dl>
 <dt>supports_condition</dt>
 <dd>
-  evaluate the single child term
+  The result is the result of the single child term.
 </dd>
 
 <dt>supports_negation</dt>
 <dd>
-  negate the result of evaluating the single child term
+  The result is the <em>negation</em> of the result of the
+  <code>supports_condition_in_parens</code> child term.
 </dd>
 
 <dt>supports_conjunction</dt>
 <dd>
-  true if all of the (non-''and'') child terms are true, otherwise false
+  The result is true if the result of <em>all</em> of the
+  <code>supports_condition_in_parens</code> child terms is true;
+  otherwise it is false.
 </dd>
 
 <dt>supports_disjunction</dt>
 <dd>
-  true if any of the (non-''or'') child terms are true, otherwise false
+  The result is true if the result of <em>any</em> of the
+  <code>supports_condition_in_parens</code> child terms is true;
+  otherwise it is false.
 </dd>
 
 <dt>supports_condition_in_parens</dt>
 <dd>
-  evaluate the single (non-''('' and non-'')'') child term
+  The result is the result of the single <code>supports_condition</code>
+  or <code>supports_declaration_condition</code> child term.
 </dd>
 
 <dt>supports_declaration_condition</dt>
 <dd>
-  true if the user agent supports the declaration (which is the same
-  as the rule for whether the user agent parses the declaration),
-  otherwise false
-  <span class="issue">Need more normative prose here; probably some in the
-  snapshot which we (unfortunately) need to copy rather than cite.</span>
+  The result is whether the CSS processor <a
+  href="#support-definition">supports</a> the declaration.
 </dd>
 </dl>
 
-<p>and the condition of the '@supports' rule is the
-condition thus described for the <code>supports_rule</code> term.</p>
+<p>The condition of the '@supports' rule is the result of the
+<code>supports_condition</code> term that is a child of the
+<code>supports_rule</code> term.</p>
 
 <div class="example">
 <p>For example, the following rule</p>
@@ -499,6 +503,34 @@ <h2 id="at-supports">Feature queries: the '@supports' rule</h2>
 }</pre>
 </div>
 
+<h3 id="support-definition">Definition of support</h3>
+
+<p>A CSS processor is considered to <dfn id="dfn-support">support</dfn>
+a declaration (consisting of a property and value) if it implements the
+given value of the given property.</p>
+
+<h3 id="partial-implementations">Partial implementations</h3>
+
+<p>For forward-compatibility, <a
+href="http://www.w3.org/TR/CSS21/syndata.html#declaration">section 4.1.8
+(Declarations and properties)</a> of [[!CSS21]] defines rules for
+handling invalid properties and values.  CSS processors that partially
+implement a specification <strong>must</strong> treat any part of a
+value that they:</p>
+<ul>
+  <li>do not implement, or</li>
+  <li>do not have a usable level of support for,</li>
+</ul>
+<p>as invalid according to this rule, and <strong>must not</strong>
+accept or support a declaration containing such a value.  This allows
+authors to use fallback (either in the [[CSS1]] sense of declarations
+that are overridden by later declarations or with the new capabilities
+provided by the ''@supports'' rule in this specification) that works
+correctly for the features implemented.  This applies especially to
+compound values; implementations must implement all parts of the value
+in order to consider the declaration supported, either inside a ruleset
+or in the declaration condition of an ''@supports'' rule.</p>
+
 <h2 id="at-document">Document queries: the '@document' rule</h2>
 
 <p>The <dfn>'@document' rule</dfn> is a conditional group