Replace out-of-range escaped with U+FFFD.

Author: tabatkins

css3-syntax/parsing.html

@@ -1434,7 +1434,10 @@ <h4>
 			<i>whitespace</i>,
 			consume it as well.
 			Interpret the <i>hex digits</i> as a hexadecimal number.
-			Return the character with that codepoint.
+			If this number is greater than 
+			the current maximum allowed codepoint in Unicode (currently U+10FFFF),
+			return U+FFFD REPLACEMENT CHARACTER.
+			Otherwise, return the character with that codepoint.
 
 		<dt>anything else
 		<dd>