final public function process_change($changetype, $oldvalue) {
        // Check the type of change requested.
        switch ($changetype) {
            // Process a status change.
            case base_setting::CHANGED_STATUS:
                return $this->process_status_change($oldvalue);
            // Process a visibility change.
            case base_setting::CHANGED_VISIBILITY:
                return $this->process_visibility_change($oldvalue);
            // Process a value change.
            case base_setting::CHANGED_VALUE:
                return $this->process_value_change($oldvalue);
        }
        // Throw an exception if we get this far.
        throw new backup_ui_exception('unknownchangetype');
    }