[Zope] The inverse of REQUEST.set is ??

I can do <dtml-call "REQUEST.set('something','whatever')"> Having done that, I'd like to be able delete 'something' and I do NOT mean just <dtml-call "REQUEST.set('something','')"> I want it gone! Come on, humor me... is there a good way to do this? -- Dennis Nichols nichols@tradingconnections.com