rap-sppi-02 EXTENDS clause instance mapping??

["Rawlins, Diana" <Diana.Rawlins@wcom.com>]

How is an EXTENDS instance related / associated with a specific base
instance? For example how is an instance of the frwkIpFilterTable map to the
appropriate instance of frwkBaseFilterTable?

I'm not seeing any description of the mechanism associating an extends
instance and its base instance in the SPPI and/or the Framework Policy
Information Base draft -- maybe I'm seeing and not understanding ;-)  

Also, can an EXTENDS PRC be specified as the base for another EXTENDS PRC?

Thanks,
Diana