title: html text box that automatically adds characters
body: <p>Hey guys I'm trying to make a HTML text box that:
  1) only accepts numbers
  2) after 3 digits, adds a '.'
  3) after 6 digits, adds another '.'</p>
  
  <p>So for example, by only typing numbers, you'll get
  555.323.7637</p>
  
  <p>4) If you're after a '.', like '555.', then a backspace would change it to '55'.</p>
  
  <p>I've been googling around but don't know the exact term I'm looking for.</p>
  
  <p>Thanks!</p>