[css-values] Clarify relative URL handling for embedded style sheets.

Author: fantasai

css-values/Overview.html

@@ -797,7 +797,9 @@ <h3 id=urls><span class=secno>3.4. </span> Resource Locators: the ‘<a
    rel=biblioentry>[URI]<!--{{!URI}}--></a>) are resolved to full URIs using
    a base URI. RFC 3986, section 3, defines the normative algorithm for
    this process. For CSS style sheets, the base URI is that of the style
-   sheet, not that of the source document.
+   sheet itself, which is not necessarily that of the source document. Style
+   sheets embedded within a document must use the base URL associated with
+   their container.
 
   <p>When a <a href="#url-value"><i>&lt;url></i></a> appears in the computed
    value of a property, it is resolved to an absolute URL, as described in
@@ -2376,6 +2378,8 @@ <h2 class=no-num id=changes>Changes</h2>
     href="#identifier-value"><var>&lt;custom-ident></var></a>. Require specs
     referencing it to be clear about excluded keywords, because the new rule
     isn't as simple.
+
+   <li>Clarified relative URL resolution for embedded style sheets.
   </ul>
 
   <p>Changes since the <a

css-values/Overview.src.html

@@ -460,8 +460,11 @@ <h3 id="urls">
 	the absolute location of a resource, authors should use relative URIs.
 	Relative URIs (as defined in [[!URI]]) are resolved to full URIs
 	using a base URI. RFC&nbsp;3986, section&nbsp;3, defines the normative
-	algorithm for this process. For CSS style sheets, the base URI is that
-	of the style sheet, not that of the source document.
+	algorithm for this process.
+	For CSS style sheets, the base URI is that of the style sheet itself,
+	which is not necessarily that of the source document.
+	Style sheets embedded within a document must use
+	the base URL associated with their container.
 
 	<p>When a <i>&lt;url></i> appears in the computed value of a property,
 	it is resolved to an absolute URL, as described in the preceding
@@ -1852,6 +1855,7 @@ <h2 class="no-num" id="changes">Changes</h2>
     <li>Relaxed unnecessary restrictions on <var>&lt;custom-ident></var>.
         Require specs referencing it to be clear about excluded keywords,
         because the new rule isn't as simple.
+    <li>Clarified relative URL resolution for embedded style sheets.
   </ul>
 
   <p>Changes since the <a href="http://www.w3.org/TR/2012/CR-css3-values-20120828/">28 August 2012 Candidate Recommendation</a> are: