See code:
case 'x':
$chr = substr( $code, $offset + 2, 2 );
if ( preg_match( '/^[0-9A-Fa-f]{2}$/', $chr ) ) {
$token .= chr( hexdec( $chr ) );
// \xXX -- 2 done later
$offset += 2;
} else {
$token .= 'x';
}
break;It tries to parse hex codepoints in literals, and that's OK. However, when it cannot parse a hex, it will add 'x' to the string, and not '\x' as it found. This is usually equivalent, but sometimes it's not. For instance, inside regexps: see https://en.wiktionary.org/wiki/Special:AbuseFilter/106.