Sanitization of User-Supplied Regular Expressions in PHP

Question

I want to create a website where users can test regular expressions (there are many out there already...such as this one: http://www.pagecolumn.com/tool/pregtest.htm). Basic

Answer 1

The only problem I can think of is that someone can DOS you by entering a bad regex (one that is O(2^n) or O(n!) or whatever), and the easiest way to prevent this might be to set your page timeout short.