[Zope] ZClass 'UNSLICEABLE OBJECT' Error Value

[Eric Roby]

I am trying to create specialized document classes that have unique
propertysheets, methods,  are CatalogAware and renderable via <dtml-var
...>.  I have been able to successfully build a structured-text document
class that meets these criteria, however, I am unable to build an HTML
document class.  If I try to use OFS:DTMLDocument or OFS:DTMLMethod as my
base class,  the ZInstance attempt throws a TypeError with a value of
'unsliceable object'.  I have tried many variations on this theme and none
were successful.  I thought I had a handle on ZClasses but I am obviously
missing something major.  Note: not that this has anything to do with the
above, but I can subclass OFS:File and OFS:Image with no problem.  I am
using Zope version 2.3.1 on a Win2K platform.

Any hints, insight, direction, further-reading links would be greatly
appreciated.

Thanks in advance...

Eric