Script so a user wouldnt screw up the rest of the page?

[cowax]

Is there a script or tag of somesort that will end all tags within it?

Example:
A user puts this as a message in a BBS that allows html:

<tag>
<table><tr><td><font color=blue>yada

</tag>

That </tag> would end the table and font tags. Is there such a thing?

[jetalomar]

fi this is for a forum, disable html format and use the forum's code.

[cowax]

Yeah I know that, but lets say I wanted to enable html. Really, all I want to do is end the table tag without breaking the table its already in.