C＃Regular Expression来验证日期？

I am trying to validate a date entered into a text box. There is an input mask on the textbox which forces input of xx/xx/xxxx. I am trying to use a regular expression validator to enforce that a correct date is entered. I am not skilled in RegEx bascially at all. My co-worker found this one on the internet but I can't really tell what it's doing.I am trying to validate a date entered into a t