title: How to make regular expression of PAN to progressive regular expression
body: <p>I want to make progressive regex of PAN number.</p>
  
  <p>My PAN number regular expression is <code>"/^([a-zA-Z]){5}([0-9]){4}([a-zA-Z]){1}$/"</code></p>
  
  <p>Format of PAN number -'AAAAADDDDA'  A- Alphabets, D- Digits</p>
  
  <p>Why I want to make progressive regex?</p>
  
  <p>I am using angular directive to set validations on input field. In that I am facing problem to my PAN regex but it works fine for progressive regex. Check here my <a href="http://plnkr.co/edit/i35OXhcvk6sLfyWvB5GL?p=preview" rel="nofollow noreferrer">plunker</a></p>
  
  <p>Referred question <a href="https://stackoverflow.com/questions/18241558/angularjs-validate-input-and-prevent-change-if-invalid">angularjs validate input and prevent change if invalid</a></p>
  
  <p>Can any one please suggest me how to do this?</p>
  
  <p>Thank you.</p>