Fun indeed. And you're right -- because those triangles were used to expand folder contents.
Upvoting, hmm... well together with downvoting, you could appropriate the number spinner/stepper widget [1], the tiny little up and down buttons attached to the right side of a number field? I'm not sure that was ever native to the Platinum design language [2], but IIRC Microsoft Office at least used it at the time.
EDIT: whoops, cmrdporcupine's sibling comment basically says the same thing. Leaving this comment here in case anyone's interested in the additional links.
Upvoting, hmm... well together with downvoting, you could appropriate the number spinner/stepper widget [1], the tiny little up and down buttons attached to the right side of a number field? I'm not sure that was ever native to the Platinum design language [2], but IIRC Microsoft Office at least used it at the time.
[1] https://en.wikipedia.org/wiki/Spinner_(computing)
[2] https://en.wikipedia.org/wiki/Appearance_Manager
EDIT: whoops, cmrdporcupine's sibling comment basically says the same thing. Leaving this comment here in case anyone's interested in the additional links.