[Zope] Zcatalog's TextIndex Question

[Ping Lau]

Can anyone explain why TextIndex only works with words but not numbers?  For
example, I have a catalogaware ZClass with a property PONumber of type
String.  I created a PONumber as TextIndex in the Catalog.  I created 3
instances of the ZClass with PONumber Verbal, Tim Dunken, 289-4569.  When I
search for Verbal, Tim, or Dunken, I get the result.  But searching for 289,
4569, or 289-4569 returns a blank page.

How can I solve the problem?

Regards,
Ping