php - Clean user input using preg_replace_callback and ord()?
function replaceHTML ($match) {
    return "&#" . ord ($match[0]) . ";";
}

$clean = preg_replace_callback ( "/[^ a-zA-Z0-9]/", "replaceHTML", $userInput );

$clean = preg_replace_callback('/[^a-z0-9s]/i', 'htmlentities', $userInput);