Odd/undocumented precedence of concatenation operator

Trying to execute the following query on PostgreSQL 9.4.4:

select 'a' >= 'b' || 'c';

Gives the result "falsec", implying that the precedence of the string concatenation operator is lower than the comparison operator. Changing the >= into = provides the result false, which is less surprising.

Is this the expected behavior, considering that >= and = behave differently and that + ranks much higher?

If nothing else, it seems that the concatenation operator should be listed on the operator precedence table at http://www.postgresql.org/docs/9.4/static/sql-syntax-lexical.html#SQL-PRECEDENCE-TABLE?

Thanks!

Shay