protected function get_response_type() {

		if ( is_array( $this->callback_response ) ) {
			$response_type = 'json';

		} elseif ( is_string( $this->callback_response ) ) {
			$response_type = 'plain';

		} else {
			// For everything else, i.e. null, WP_Error object, caught exception, etc.
			$response_type = 'error';
		}

		return $response_type;
	}