title: How to validate the text box should take only A B C
body: <p>I have a text box I need to validate that.. </p>
  
  <p>I mean user can only Enter Either A or B or C if he enters D to Z or any other things I should show the Popup message please Enter A or B or C</p>
  
  <p>Using Jquery or javascript?</p>
  
  <p>thanks</p>