$y = ($x = true and false);
var_dump($x); //outputs bool(true)
var_dump($y); //outputs bool(false)

This is a case of mistaken operator precedence. In this example, the assignment operator (=) has higher precedence than the 'and' operator, so $x is assigned the value true. The second example clears things up a bit. After the first assignment to $x, the return value (true) is anded with false, yielding false, which is assigned to $y.