[css-syntax] Clarify @charest vs. ASCII-incompatible encodings.

Author: SimonSapin

css-syntax/Overview.html

@@ -54,7 +54,7 @@
 </p>
   <h1 class="p-name no-ref" id=title>CSS Syntax Module Level 3</h1>
   <h2 class="no-num no-toc no-ref heading settled heading" id=subtitle><span class=content>Editor’s Draft,
-    <span class=dt-updated><span class=value-title title=20140103>3 January 2014</span></span></span></h2>
+    <span class=dt-updated><span class=value-title title=20140108>8 January 2014</span></span></span></h2>
   <div data-fill-with=spec-metadata><dl><dt>This version:<dd><a class=u-url href=http://dev.w3.org/csswg/css-syntax/>http://dev.w3.org/csswg/css-syntax/</a><dt>Latest version:<dd><a href=http://www.w3.org/TR/css-syntax-3/>http://www.w3.org/TR/css-syntax-3/</a><dt>Editor’s Draft:<dd><a href=http://dev.w3.org/csswg/css-syntax/>http://dev.w3.org/csswg/css-syntax/</a><dt>Previous Versions:<dd><a href=http://www.w3.org/TR/2013/WD-css-syntax-3-20131105/ rel=previous>http://www.w3.org/TR/2013/WD-css-syntax-3-20131105/</a><dd><a href=http://www.w3.org/TR/2013/WD-css-syntax-3-20130919/ rel=previous>http://www.w3.org/TR/2013/WD-css-syntax-3-20130919/</a>
     <dt>Feedback:</dt>
         <dd><a href="mailto:www-style@w3.org?subject=%5Bcss-syntax%5D%20feedback">www-style@w3.org</a>
@@ -464,12 +464,17 @@ <h3 class="heading settled heading" data-level=3.2 id=input-byte-stream><span cl
 			is the string "<code>@charset "…";</code>",
 			where the "…" is the sequence of bytes corresponding to the encoding’s label.
 
-<p>			If the return value was <code>utf-16</code> or <code>utf-16be</code>,
+<p>			If the return value was <code>utf-16be</code> or <code>utf-16le</code>,
 			use <code>utf-8</code> as the fallback encoding;
 			if it was anything else except failure,
 			use the return value as the fallback encoding.
 
-<p class=note>			Note: This mimics HTML <code>&lt;meta&gt;</code> behavior.
+<p class=note>			Note: UTF-16BE and UTF-16LE are the only ASCII-incompatible encodings that
+			<a href=http://encoding.spec.whatwg.org/#concept-encoding-get>get an encoding</a>
+			can return.
+			Using one of them to decode the ASCII <code>@charset "…";</code> byte sequence
+			would result in garbage.
+			This mimics HTML <code>&lt;meta&gt;</code> behavior.
 
 		<li>
 			Otherwise, if an <a data-link-type=dfn href=#environment-encoding0 title="environment encoding">environment encoding</a> is provided by the referring document,

css-syntax/Overview.src.html

@@ -301,12 +301,17 @@ <h3 id="input-byte-stream">
 			is the string "<code>@charset "…";</code>",
 			where the "…" is the sequence of bytes corresponding to the encoding's label.
 
-			If the return value was <code>utf-16</code> or <code>utf-16be</code>,
+			If the return value was <code>utf-16be</code> or <code>utf-16le</code>,
 			use <code>utf-8</code> as the fallback encoding;
 			if it was anything else except failure,
 			use the return value as the fallback encoding.
 
-			Note: This mimics HTML <code>&lt;meta></code> behavior.
+			Note: UTF-16BE and UTF-16LE are the only ASCII-incompatible encodings that
+			<a href="http://encoding.spec.whatwg.org/#concept-encoding-get">get an encoding</a>
+			can return.
+			Using one of them to decode the ASCII <code>@charset "…";</code> byte sequence
+			would result in garbage.
+			This mimics HTML <code>&lt;meta></code> behavior.
 
 		<li>
 			Otherwise, if an <a>environment encoding</a> is provided by the referring document,