array + index == index + array needs justification

One expects the generic + in a+i to get expanded to raw addition .+. and raw multiplication .x. with s the size of elements of the array

    a .+. s .x. i

One expects index + array to throw a type error because index is just a number and doesn't have an element size.

So I'm guessing that the real reason that the trick works is that generic + has three methods with signatures

    int + int
    array + int
    int + array