Missing prefix unary '+' operator in Table 4-2 ?

I have question about Table 4-2. Operator Precedence (decreasing) on
http://www.postgresql.org/docs/9.0/static/sql-syntax-lexical.html. I
see there is '-' unary (unary minus) operator listed, but I can't see
'+' (unary plus) prefix operator there. I think that it does not
belong to "(any other)" group as:

SELECT 5 ! + 6;
ERROR:  operator does not exist: integer ! integer
LINE 1: SELECT 5 ! + 6;

Regards,
Grzegorz Szpetkowski