extra syntax on INSERT

I just realized that INSERT allows us to have more syntax than the
manual said. I wonder if we want to elimiate it or keep it with more
documentation on the INSERT statment?

Here is the INSERT synopsis we have in 7.2 documentation.
==========
INSERT INTO table [ ( column [, ...] ) ]
{ DEFAULT VALUES | VALUES ( expression [, ...] ) | SELECT query }

Assume we have,
CREATE TABLE t1 (a1 int, a2 int);
CREATE TABLE t2 (a3 int, a4 int);

INSERT INTO t2 VALUES(2, 0);
INSERT INTO t2 VALUES(2,1);

==== postgres allows to have something like ====

INSERT INTO t1 VALUES(1, 0 AS "Oops");
INSRET INTO t1 VALUES(t2.*);

===================

For the first one, I believe that is due to reusing the definition of
target_list/target_el. I didn't dig in to see how PostgreSQL handle the
second case. At least the INSRET synopsis does not cover this case.

--
Regards,
LM Liu