function _simpleAsString(modifiers, key, labels) {
        if (key === null) {
            return '';
        }
        var result = [];
        // translate modifier keys: Ctrl-Shift-Alt-Meta
        if (modifiers.ctrlKey) {
            result.push(labels.ctrlKey);
        }
        if (modifiers.shiftKey) {
            result.push(labels.shiftKey);
        }
        if (modifiers.altKey) {
            result.push(labels.altKey);
        }
        if (modifiers.metaKey) {
            result.push(labels.metaKey);
        }
        // the actual key
        result.push(key);
        return result.join(labels.separator);
    }
A label provider that prints modifiers in a suitable format for user settings.