Irrlicht Engine

I don't like the idea of breaking backwards compatibility, and maybe this has been brought up before, but it seems the naming is wrong for the content of the functions. They should be switched. The comments describing them are accurate for the name but not for the code. (And notably, the rect<T>& and rect<T> returns would need to be swapped.)
But it makes me wonder - is there somewhere in the engine where these are being used? I haven't checked yet - maybe someone else has.

Walking around the problem is easy enough - you simply do it manually. Nevertheless, it renders the functions ambiguous and therefore not as useful, no pun intended.

I find no delta functions in rect.h. Could this be some functions you added yourself to the header?

Could be. lol. I don't remember anything I've modded in the file since I haven't touched in it a long time.