Pavel Stehule <pavel(dot)stehule(at)gmail(dot)com> writes:
> 2009/10/22 Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us>:
>> It is not --- it's the recommended solution for emulating computed
>> columns. The column-as-f(x) direction maybe isn't terribly exciting,
>> but the function-as-x.col direction definitely is.
> is it documented?
Yes, see "SQL Functions on Composite Types" (34.4.2 as of CVS HEAD),
down near the end of that subsection.
regards, tom lane