[Zope] Cataloging ZClasses which are subclasses of a ZClass?

[Darran Edmundson]

To use a well-worn metaphor, I continue my steep
climb up the Zope learning curve (top-roped by the
able members of this list).  Today I struggled with
ZCatalog-aware ZClasses.  

I have been toying with a simple example - a URLClass
nested beneath a URLFolderProduct and URLFolderClass.  
URLClass is catalog-aware and, among others, has a 
string property for the URL (note, beware of naming a 
ZClass property "URL").  This all works - I can create 
a URLFolder and instances of URLClass within it.

Now I add a "singleton" (by virtue of me only creating
one instance?) ZCatalog in the URLFolder.  My problem is 
that the URLClass's meta-type does not show up in the 
ZCatalog's "Find items to ZCatalog" tab.  (This seems
reminiscent of the ZClass ID bug.)  If URLClass
is created in the Product root (and thus able to be
added anywhere rather than just in URLFolder objects),
it shows up in said Catalog tab selection box.

Eventually I want to move on and have my URLFolder
subclassed from ZCatalog as discussed in:
   http://www.zope.org/Members/tseaver/inherit_ZCatalog
but I won't proceed with this until I have this
basic example worked out.

As always, any help is much appreciated.

Darran.