Imagine a `Context` object and some related files:

    Context.slul
    Parser.slul
    Tokenizer.slul

Is it a good idea to let files extend the `Context` class?
For example, to have something like this in `Parser.slul`:

    part of Context

    local String buffer
    local int offset

    func parse
    ...

Then `buffer`, `offset`, `parse` would be part of the `Context` object,
although `buffer` and `offset` would not be visible in other files.