A < bopwI’ > would be a topic, the way I see it.
It may be a word that has to be used always with something else, similar to "-monger" in English. It means "someone who trades in / who peddles", but you never use "monger" on its own, it doesn't make sense because you always need to specify what is being peddled, so you get "fishmonger", "rumourmonger"...
Similarly with < bopwI' >, it's "something which concerns/is about", so you'd always need to specify "what" it is about, by putting a noun before < bopwI' >.
thus you'd get < QeD bopwI’ > for "science topic" for instance.
At least that's my theory on how it works, who knows what matlh would have to say about this ? :)