It is important that the holder of a capability be unable to distinguish properties of the capability aside from invoking the capability or sending the capability to another object via a held capability.
It is usually assumed that a program can act conditionally on properties of an integer that it holds such as whether the integer is odd. Thus one might assume similar abilities with regards to a capability.
Keykos provides the DISCRIM key to all customers who may choose to run programs without access to DISCRIM. With DISCRIM one can distinguish among a few categories of keys (capabilities).