When adding comments with the /x modifier, don't use the pattern delimiter in the comments. It may not be ignored in the comments area. Example:

<?php
$target = 'some text';
if(preg_match('/
                e # Comments here
               /x',$target)) {
    print "Target 1 hit.\n";
}
if(preg_match('/
                e # /Comments here with slash
               /x',$target)) {
    print "Target 1 hit.\n";
}
?>

prints "Target 1 hit." but then generates a PHP warning message for the second preg_match():

Warning:  preg_match() [function.preg-match]: Unknown modifier 'C' in /ebarnard/x-modifier.php on line 11