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.