What are cameras classes in Doom progs? And why they are only there?

I think they come from Doom Legacy (another Doom source port), they should work with ACS scripts, but I don't know if Vavoom is missing a "set player view" function or something (which is how ZDoom cameras actually work), in a word... I don't really know if they actually work or they are just placeholders for some functionality that will be added in the future (which is my guess).

They are from ZDoom, added mostly as a test, but without possibility to set player view object they are not very usefull.