title: Validation textbox in winforms
body: <p>How to validate text in textbox control in winforms?<br>
  I have a control, where user have to put string, like "13:55". I want to show MessageBox, when this value will be diffrent, than "XX:YY". <br>
  How to do it?<br>
  In asp.net it was so easy to make, but how to implement it on winforms?</p>