Well, if you do an XOR of two strings (scalars that haven't been used as numbers), perl will do a bitwise XOR on the characters of the strings, instead of the bits on the numbers. Two characters that are the same will have all the bits the same, XORing those characters will give you the character of which all the bits are 0, aka "\x00". If two characters are not the same, there is at least one bitpositions where the bits are different - resulting in a 1 bit when XORing. Hence, the resulting character will be anything but "\x00".

Abigail