Switch character case, php

Question

How can I swap around / toggle the case of the characters in a string, for example:

$str = \"Hello, My Name is Tom\";

After I run the code

Answer 1

Very similar in function to the answer by Mark.

preg_replace_callback(
    '/[a-z]/i',
    function($matches) {
        return $matches[0] ^ ' ';
    },
    $str
)