Swift flatmap and regex matches

gistfile1.txt

func matches(for regex: String, in text: String) -> [String] {

    do {
        let regex = try NSRegularExpression(pattern: regex)
        let results = regex.matches(in: text,
                                    range: NSRange(text.startIndex..., in: text))
        return results.map {
            String(text[Range($0.range, in: text)!])
        }
    } catch let error {
        print("invalid regex: \(error.localizedDescription)")
        return []
    }
}

let stringS = ["RLRLRL","RRLL","LLRRRLRLR","RRRLLLLRLRLR"]
.flatMap({
    matches(for: "(RL)|(LR)|(R{2}L{2})", in: $0)
})