MSDN has this, and I have never seen a comment there that actually provided value to a reader of the page. It makes even less sense on MDN, because MDN is a wiki; if you think something is missing, you can get it added.
https://secure.php.net/manual/en/function.htmlspecialchars.p...
https://secure.php.net/manual/en/function.preg-replace.php#u...
https://secure.php.net/manual/en/function.header.php#usernot...