public function offsetGet($offset)
    {
        if (is_int($offset)) {
            return $this->contents[$offset];
        } elseif ($offset == ':last') {
            // Shortcut for fetching the last item in the Collection:
            return $this->contents[count($this->contents) - 1];
        } else {
            return $this->callSelector($offset);
        }
    }