src/vs/workbench/services/actions/common/menusExtensionPoint.ts/isValidSubmenu
	export function isValidSubmenu(submenu: IUserFriendlySubmenu, collector: ExtensionMessageCollector): boolean {
		if (typeof submenu !== 'object') {
			collector.error(localize('require', "submenu items must be an object"));
			return false;
		}

		if (typeof submenu.id !== 'string') {
			collector.error(localize('requirestring', "property `{0}` is mandatory and must be of type `string`", 'id'));
			return false;
		}
		if (typeof submenu.label !== 'string') {
			collector.error(localize('requirestring', "property `{0}` is mandatory and must be of type `string`", 'label'));
			return false;
		}

		return true;
	}