8 interface ExpressibleInterface
11 * Get the contained value as string
14 function __toString();
17 * Test whether we are an expression
23 * Get the literal value or the expression
29 * Set the contained value
31 * @return \pq\Query\ExpressibleInterface
38 * @param string $op a specific operator
39 * @return \pq\Query\ExpressibleInterface
41 function mod($data, $op = null);