Creating new slot options

[Michael DeBellis <debellis@andersen.com>]

I would like to add new options to slots.  For example I would like
to be able to state the cardinality (legal number of values) and value-class 
of a slot.  I would like the value class to be much more than the :tyype
option since I want the system to take action when it encounters a value that 
does not satisfy a value-class (e.g. warn the user and enable her/him to fix
it).  

Essentially what I want is to add "facets" as they are used in KEE and
other Frame oriented languages.  It seems to me that the best way to
do this is to create my own slot options.  Is this possible?  If possible
how difficult is it?  Would I have to get into PCL internals?  Is 
there a better way to do it?

Thanks in Advance
Mike DeBellis