Accessing an array element from a function

This may be mostly a documention issue:

I have a function with two parameters that returns an array: text[].

I want to access just the first element of that array within
my SQL statement.

This doesn't work:

    select myfunc(1,2)[1];

This does work:
    select (myfunc(1,2)[1];

If that's how it's supposed to work, is that documented somewhere?
--
Mike Nolan