Is there any documentation on restriction of HTML/CSS?

[thirteen13stuff]

So on my forum, specifically in this thread, the posting scripts in #3 and #4 have become somewhat of a mess. On my own personal Jcink forum, they work fine so I assume this problem has been caused by certain restrictions on HTML/CSS for security reasons. Rather than try and subvert this, I was wondering if there was any documentation on such restrictions. Now, I have looked through the documents on this site (specifically those pertaining to security) but I haven't really found any relevant information. Any pointers?