Cannot mark number-named fields as optional

[lua-rocks]

Here is a vector class:

It must necessarily have 2 values. I can't give them alphabetic names because for the position subclass they are x and y and for the size they are w and h, so I use numeric names [1] and [2].

This class accepts optionally 2 extra number-named fields and field "units". As you can see, I can mark units with a question mark, but I can't mark number fields (3 and 4 in this example) as optional.

PS: Also it would be cool if you could just let the fields be called 1, 2, 3... instead of [1], [2], [3]...