<?php

/**
 * Uppercase to lowercase and lowercase to uppercase(ASCII string only).
 *
 * @param  string $value
:x * @return string
 */
function invertCase($value)
{
    return strtolower($value) ^ strtoupper($value) ^ $value;
}

// echo invertCase("Invert My CASE");
// => iNVERT mY case