src/vs/workbench/contrib/codeEditor/browser/languageConfigurationExtensionPoint.ts/isStringArr
function isStringArr(something: string[] | null): something is string[] {
	if (!Array.isArray(something)) {
		return false;
	}
	for (let i = 0, len = something.length; i < len; i++) {
		if (typeof something[i] !== 'string') {
			return false;
		}
	}
	return true;

}