These operators can be used in joining two seperate where clauses, $a and $b

Example	Name	Result
array('$a', 'and', '$b')	AND	TRUE if both $a and $b are TRUE
array('$a', 'or', '$b')	OR	TRUE if either $a or $b is TRUE
array('$a', 'xor', '$b')	XOR	TRUE if either $a or $b is TRUE, but not both.