[Zope] How to create a new TAL statement?

Hi all! As Aj and Chris advise my to forget the __getattr__ bussiness I try to solve the same question by other ways Now I have a new question: Can you point me to some help about how to create a new TAL statement? I would like to create a tal:yanged (for example) statement to control how zope give to use some properties Thanks! -- Mis Cosas http://blogs.sistes.net/Garito