public function removeCustom($index)
    {
        if (array_key_exists($index, $this->_custom)) {
            $element = $this->_custom[$index];
            // Remove element
            unset($this->_custom[$index]);
            // Re-index the array
            $this->_custom = array_values($this->_custom);
            // Be sure to delete form both arrays!
            $key = array_search($element, $this->_customByName);
            unset($this->_customByName[$key]);
        } else {
            require_once 'Zend/Gdata/App/InvalidArgumentException.php';
            throw new Zend_Gdata_App_InvalidArgumentException(
                'Element does not exist.');
        }
        return $this;
    }