Unclear documentation

In the CREATE FUNCTION docs I notice this:

RETURNS NULL ON NULL INPUT or STRICT indicates that the function always
returns null whenever any of its arguments are null. If this parameter
is specified, the function is not executed when there are null
arguments; instead a null result is assumed automatically.

I'm wondering what this means when the function returns a composite
type, or a setof scalar or a setof composite?

So if you indicate STRICT, does PostgreSQL assume one row of all nulls
for each column in the return composite type? Perhaps someone who knows
better could tweak the docs a bit?

Cheers,

Chris