Description:
------------
It would be useful to document the following:
mysql_affected_rows() DOES NOT count rows affected implicitly through 'ON DELETE CASCADE' and/or 'ON UPDATE CASCADE' foreign keys.

Reproduce code:
---------------
---
From manual page: function.mysql-affected-rows
---
CREATE TABLE `types` (
  `type` varchar(10) NOT NULL,
  PRIMARY KEY (`type`)
) ENGINE=InnoDB;

CREATE TABLE `symbols` (
  `symbol` char(1) NOT NULL,
  `type` varchar(10) NOT NULL,
  PRIMARY KEY (`symbol`),
  KEY `FK_symbol_type` (`type`)
) ENGINE=InnoDB;

ALTER TABLE `symbols`
  ADD CONSTRAINT `FK_symbol_type` FOREIGN KEY (`type`) REFERENCES `types` (`type`) ON DELETE CASCADE ON UPDATE CASCADE;

INSERT INTO `types` VALUES ('Number'), ('Letter');
INSERT INTO `symbols` VALUES ('1', 'Number'), ('2', 'Number'), ('A', 'Letter'), ('B', 'Letter');

<?php
mysql_query('UPDATE types SET type = "Digit" WHERE type = "Number"');
echo mysql_affected_rows() . '<br>';

mysql_query('DELETE FROM types WHERE type = "Letter"');
echo mysql_affected_rows() . '<br>';
?>

Expected result:
----------------
Each query actually affects 3 rows (1 type + 2 symbols), but output is:
1
1

Actual result:
--------------
That's OK, but needs to be documented.