[css-syntax] Per WG resolution, filter surrogates from the input stream. Fixes #3307.

Author: tabatkins

css-syntax-3/Overview.bs

@@ -419,7 +419,7 @@ Preprocessing the input stream</h3>
 			by a single U+000A LINE FEED (LF) <a>code point</a>.
 
 		<li>
-			Replace any U+0000 NULL <a>code point</a> with U+FFFD REPLACEMENT CHARACTER (�).
+			Replace any U+0000 NULL or <a>surrogate</a> <a>code points</a> with U+FFFD REPLACEMENT CHARACTER (�).
 	</ul>
 
 
@@ -3446,6 +3446,9 @@ Changes from the 20 February 2014 Candidate Recommendation</h3>
 
 	* Removed the Selectors-specific tokens, per WG resolution.
 
+	* Filtered <a>surrogates</a> from the input stream, per WG resolution.
+		Now the entire specification operates only on <a>scalar values</a>.
+
 	The following editorial changes were made:
 
 	* The "Consume a string token" algorithm was changed to allow calling it without specifying an explicit ending token,