Ensuring users have provided valid html

[Peter Hardy]

Hi guys,

I am trying to develop a mini e-learning application where the user provides
content for each page. Eventually, I'd like to shift to using templates but
at the moment the users is just entering content using html. Whats the best
way to allow the user to do this and whats the best way of ensuring the html
is valid before I store it in my database / xml document?

Cheers,

Peter Hardy