<p>How do I limit the types of HTML that a user can input into a textbox? I'm running a small forum using some custom software that I'm beta testing, but I need to know how to limit the HTML input. Any suggestions?</p>

Once the text is submitted, you could strip any/all tags that don't match your predefined set using a regex in PHP.
It would look something like the following:
```
```
find open tag (<)
if contents != allowed tag, remove tag (from <..>)
```
```