title: UWP - Textbox Validation Sign
body: <p>I am trying to implement a Textbox which has a validation sign at the end next to the "X" which shows up, when the input is valid. The DataTemplate implementation is no problem but I am unsure on how to implement the logic.</p>
  
  <p>One way would be a TextChanged event and then try to access the ValidSign element inside the DataTemplate. But I am not very fond of this method.</p>
  
  <p>Is there a way to extend the TextBox logic since there must be some code-behind for the "X" button in the first place?</p>