[Zope] setting Zclass instance id based on properties

[Charlie Kalech]

I would like to set the id of a Zclass instance based on some of the properties

I can not use the property variables in the add method since the 
properties have not yet been assigned a value

For instance let's say I have three properties: Section, Chapter and Page

How do I assign the id the value <dtml-var Section>-<dtml-var 
Chapter>-<dtml-var Page> when I create the zclass instance?