PHP compatibility

These are intentional differences from the PHP specification. In many cases, solving a notice or warning generated by PHP will also solve the error returned by the parser.

Expressions

RHS of byref assignments cannot be an invocation expression.

// Generates an E_NOTICE message.
$a =& f();

The instanceof operator is non-associative, like it's supposed to be.

$a instanceof A instanceof B;  // Works!