Description:
------------
---
From manual page: http://www.php.net/function.array-diff-key
---
The return value is specified as "Returns an array containing all the entries from array1 whose keys are not present in any of the other arrays."

On my first read, I interpreted this as how the function actually works, as revealed by testing.  However, I got in an argument with a developer who read this to mean something different, almost the opposite, a meaning I could see in the original text once pointed out.  Basically, the other developer had interpreted this as, "Returns an array containing all the entries from array1 whose keys is not present in AT LEAST ONE of the other arrays".

Whereas, the actual behavior can more precisely be stated as, "Returns an array containing all the entries from array1 whose keys are MISSING FROM ALL of the other arrays."

A three argument example like the one I entered as the test script & expected result, below, would probably help too.


Test script:
---------------
<?php
$array1 = array('blue'  => 1, 'red'  => 2, 'green'  => 3, 'purple' => 4);
$array2 = array('green' => 5, 'yellow' => 7, 'cyan'   => 8);
$array3 = array('blue' => 6, 'yellow' => 7, 'mauve'   => 8);

var_dump(array_diff_key($array1, $array2, $array3));

Expected result:
----------------
array(2) {
  ["red"]=>
  int(2)
  ["purple"]=>
  int(4)
}