help understanding markup / macro usage

[uvtc]

The docs on markup in mendoza seem to mix what I'd need as user (markup) with what I'd need as a developer writing new macros for mendoza.

As a user, I want to know what is the difference between:

@some-command[this and that]
@some-command{this and that}
@some-command[this and that]{other as well}

It looks like @some-command[this and that]`other as well` is shorthand for that last one. Correct?

I assume @some-command{other as well}[this and that] would be an error, as it appears that the brackets and braces are in the wrong order. Is that right?

As a user, it doesn't appear I'd ever need the @some-command(this and that) form, yes?