[Zope-dev] Where is has() defined?

[Kyler B. Laird]

I'm trying to read 
	python/Products/PageTemplates/Expressions.py
and
	python/OFS/Traversable.py
but I am at a loss for the definition of has().

I've been grep-ping all over the place trying
to find it, with no luck.  Is it a Python 2.1
thing?  I've tried it in a test script, but I
did not succeed.

I need a whack with the clue stick.

Thank you.

--kyler