title: RequiredFieldValidator to validate a disabled textBox
body: <p>I've got a TextBox in which user can input a their desired username.
  Underneath I've got a checkbox that once clicked it copies the user's email adress into the textfield and then disable it to prevent further changes. This feature is implemented by using jQuery.</p>
  
  <p>The problem is that I've got a RequiredFieldValidator on that TextBox and it looks like it can't validate a disabled textfield, even if the value is set.</p>
  
  <p>How can I solve this?</p>