^(((\d{3}[1-9]|\d{2}[1-9]\d|\d[1-9]\d{2}|[1-9]\d{3})(/)(((0[13578]|1[02])(/)(0[1-9]|[12]\d|3[01]))|((0[469]|11)(/)(0[1-9]|[12]\d|30))|(02(/)(0[1-9]|[1]\d|2[0-8]))))|(((\d{2})(0[48]|[2468][048]|[13579][26])|((0[48]|[2468][048]|[3579][26])00))(/)02(/)29))$
Match year/month/day format. e.g: 2020/02/29 [match] 2021/02/29 [mismatch] 2021/08/25 [match]