Lab is a room.
A power is a kind of an object.
A category is a kind of value.
The categories are cat-a, cat-b and cat-c.
A power has a category.
pow001 is a power. The category of pow001 is cat-a.
pow002 is a power. The category of pow002 is cat-a.
pow003 is a power. The category of pow003 is cat-a.
pow004 is a power. The category of pow004 is cat-b.
pow005 is a power. The category of pow005 is cat-b.
pow006 is a power. The category of pow006 is cat-b.
pow007 is a power. The category of pow007 is cat-c.
pow008 is a power. The category of pow008 is cat-c.
pow009 is a power. The category of pow009 is cat-c.
To decide which list of powers is the list of powers in category (c - a category):
decide on the list of c powers.
Fooing is an action applying to nothing.
Understand "foo" as fooing.
Instead of fooing:
let L be the list of powers in category cat-c;
showme L.
Test me with "foo".
Note that the phrase: decide on the list of cat-c powers. does work, but I can’t figure out how to make it work with an argument being provided.
The verb to be of category means the category property.
to decide what list of powers is the list of powers with category (c - a category):
decide on the list of powers that are of category c.
of course, you don’t really need a phrase at that point.
Easy to miss, the only reference to it in WI lurks within the discussion of units (specified kinds of value, i.e., units) in WI 15.12 where it’s described in passing and sounds like just a little bit of syntactic sugar rather than something that enables important functionality you can’t get otherwise.
You’re right, for anonymous enumerated kind of value properties you don’t need the verb, you’d only need it to do things like that with properties that don’t automatically become adjectives.