PHP manual gems

Every now and then, one comes across these mind-blowingly profound comments in the PHP manual. Post your discoveries here!

I'll start with this: (from http://www.php.net/manual/en/function.abs.php#94768)

Here is a simple function to make positives to negative and negatives to positive. This is function:

<?php
function turn($x)
     {
     $y = abs($x);
     if ($y == $x)  
         return "-$y";  
     else      
         return "$y";  
     }
?>

You can use this code:

<?php
echo turn(-5) + turn(10);
?>

The output is:

-5

;
Because 5 + -10 = -10

look on line 11 of shiichan