“Safe” markdown processor for PHP?

Question

Is there a PHP implementation of markdown suitable for using in public comments?

Basically it should only allow a subset of the markdown syntax (bold, italic, links,

Answer 1

How about running htmlspecialchars on the user entered input, before processing it through markdown? It should escape anything dangerous, but leave everything that markdown understands.

I'm trying to think of a case where this wouldn't work but can't think of anything off hand.