Currently __getitem__()/__setitem__() accept array as keys, which implicitly has to be boolean arrays, or 0d integer arrays i.e. has a working __index__(). The latter is not an obvious concept to grasp, and maybe not even quite specified anyway.

I propose we add the stdlib typing.SupportsIndex to the get/set item signatures, specifically before array. This does add support for any indexable type, but that seems okay, and was the intention anyway when __index__() was proposed in #231. I also think a note would be helpful in regards to what arrays are accepted, e.g.:

key can only be an array if it is valid for boolean array indexing, or supports __index__() i.e. is a 0-dimensional integer array.

cc @kgryte @asmeurer