Valued Predicates

In my reading of SQL for smarties I've stumbled across syntax that is supported by Postgresql.
However, I can't find mention of it in the Postgresql Docs.  Would an appropriate location for
this syntax be the "where condition" of the insert/update/select/delete statements?

i.e.

mydb=# select * from test2 where ( (a,b) >= (1,'A') ) is unknown;
 a | b
---+---
 3 |
(1 row)
mydb=# select * from test2 where ( (a,b) >= (1,'A') ) is true;
 a |   b
---+--------
 1 | Albert
 2 | Bert
(2 rows)
mydb=# select * from test2 where ( (a,b) >= (1,'A') ) is false;
 a | b
---+---
(0 rows)
mydb=# select * from test2 where ( (a,b) >= (1,'A') ) is not false;
 a |   b
---+--------
 1 | Albert
 2 | Bert
 3 |
(3 rows)
mydb=# select * from test2 where ( (a,b) >= (1,'A') ) is not true;
 a | b
---+---
 3 |
(1 row)
mydb=# select * from test2 where ( (a,b) >= (1,'A') ) is not true;
 a | b
---+---
 3 |
(1 row)

Regards,

Richard Broersma Jr.