7.2. Table Expressions FULL join is only supported with merge-joinable join conditions

http://www.postgresql.org/docs/9.0/static/queries-table-expressions.html

"The join condition specified with ON can also contain conditions that
do not relate directly to the join. This can prove useful for some
queries but needs to be thought out carefully. For example:

=> SELECT * FROM t1 LEFT JOIN t2 ON t1.num = t2.num AND t2.value = 'xxx';"

Can you add information about FULL JOIN in doc there ? I am trying to
run such query:

SELECT * FROM t1 FULL JOIN t2 ON t1.num = t2.num AND t2.value = 'xxx';
ERROR: FULL JOIN is only supported with merge-joinable join conditions

I mean add something like: "Note that you can't use such conditions
with FULL JOIN, only equality of selected columns is supported with
this type".

Thanks,
Grzegorz Szpetkowski