[Zope] Forcing

Hi, How can I force a field to just have a value type? Example: the name field will just receive letters, it can'r receive numbers. Can anyone tell me how can I do this? Another thing. Do anyone knows where I can get information about Tiny Tables? I already searched in www.zope.org, www.egroups.com, and www.google.com, but I couldn't get anything. Please send you answers to: psilva@ruido-visual.pt Thanks, Pedro