I'm fine with the above. As far as closing tags and quoting HTML elements in plain text, have you checked out ad_html_text_convert in acs-tcl/tcl/text-html-procs.tcl? I've used it elsewhere in the toolkit and it seems to work well enough.
Lars wrote it, ping him and I'm sure he can fill you in on any shortcomings.
And the ad_page_contract filter "html" scans for "bad tags" (as configured by a system param).
If you're using the form system, or my roughed-out ad_form, validate with ad_html_security_check, which is the function called by the ad_page_contract filter.
