[Zope] Selection Box

[John Glossner]

I have searched most reference material with no avail to try 
to find out how to set up a simple selection box.

I have a ZClass called LinkClassification to which I have attached
a property link_class which is assigned to value link_class_data.

My question is where do I create the variable link_class_data?
I think it should be as another property in the same directory.
When I do this the zope management screen hangs.
 
I presume this is because I did not define the link_class_data
property correctly. What are the valid types allowed for
a selection box - strings,text,etc.?

Does someone have the syntax for how the selection box is
assigned a variable? Or is there an example somewhere I 
can reference?

Thanks,
John