[Zope] Difference between id and getId()?

I am a newbie to Zoip and apologize if this is a trivial question, but it has been giving me grief for several hours now. I have found by experimentation that when iterating through a set of objects and testing their ids that the following only seems to work ONLY for folders: <dtml-if "id == 'theObjectIdString'> .... </dtml-if> If however I use the code: <dtml-if "getId() == 'theObjectIdString'> ... </dtml-if> all seems to work correctly. Obviously I am missing something very basic here. TIA Dave.