[Zope] aborting DTML parsing partway through a document.

I've got a product that gets included at the top of a document, with, eg, <!--#var mpfm_free-->. This product checks for various fields being set, inserts some HTML if they are set, but if not, I want it to insert some different HTML, then abort rendering the page any further. What's the easiest way to do this? I'd prefer not to have to put some sort of <!--#if--> wrapper around the rest of the content of each page. Do I simply have to raise an exception of some sort, with the HTML I wish to show as the value? Anthony