jvandyk raised the question whether += is officially supported by PHP as it is not in the documentation. I contacted Goba who pointed me to lxr.php.net and from there I read the relevant pieces of PHP source code and it's quite clear it does. !#@%$"!
Stop here if you are not interested in gory details. I said you should stop, right? OK, here are the details if you have not stopped:
http://lxr.php.net/search?string=T_PLUS_EQUAL
both in Zend and ZendEngine2 we can see that T_PLUS_EQUAL is executed by:
zend_do_binary_assign_op(ZEND_ASSIGN_ADD, &$$, &$1, &$3 TSRMLS_CC);
so we move on to http://lxr.php.net/search?string=ZEND_ASSIGN_ADD
RTFM :))) "In addition to the basic assignment operator, there are "combined operators" for all of the binary arithmetic and string operators that allow you to use a value in an expression and then set its value to the result of that expression. For example:" from: http://www.php.net/manual/en/language.operators.assignment.php Sometimes it does pay off reading the manual....