Actually, apparently it doesn't handle numeric character references quite right. http://www.w3.org/TR/html5/syntax.html#tokenizing-character-references has a table of values (covering `0` and most of `0x80..0x9F`) that are considered parse errors and are mapped to specific characters (I'm not quite sure why it's a parse error if it has a character you're supposed to return, I guess to give the user agent the opportunity of aborting if it wants to). So that should actually be handled.