⌷ Index r←x⌷y

If y is an array, x is a vector of integers with length less than or equal to the rank of y, and depth at most two. r is the selection of cells from axes of y, where nested entries of x indicate that multiple cells are selected, and negative x indicates indexing from the end.

If y is a dictionary, r is the item of y with key r.

Supports the origin extra argument, which offsets x by the origin (if y is an array); supports the fill extra argument, which is the default value returned when the index is out of bounds or doesn't appear in the dictionary.