Thanks for replying!

They seem to have come from a combination of two proposals, one very old, and one quite new. The old proposal did not use underscores, while the new one did. The old proposal used “rotator”, while the new one used “spinn[er|ing]”.

As far as I can tell, all of the tags on the playground equipment wiki page are formalized, just not necessarily harmonious.

No, the intention here would be to do away with the need for playground=baby_swing. As an example:

For this swing set, I would tag it as:

playground=swing
capacity=4
capacity:baby=2

And for this one:

playground=swing
capacity=8
capacity:baby=8

Similar to how capacity=* is currently used for parking spaces.