[Q] Parser behavior in a string

I noticed that PHP4 accept and does not raise error (notice messages) for following line. $arr = array('first' => 'one'); $str = "This is first element of array: $arr[first]"; //Following line cause parse error //$str = "This is first element of array: $arr['first']"; Question: Is this expected behavior that PHP parse w/o errors? If this is not a expected behavior and subject to change, I'm not going to use array w/o ' or " for assoc arrays. Because I'm going to log all error messages for production system including notice messages. Thank you. -- Yasuo Ohgaki