title: Regex comma delimited string validation
body: <p>I have a string that should be valid only if it has 2 characters and it is delimited by commas.</p>
  
  <pre><code>AD,AC,AN,JP (valid)
  AD (valid) if user enter only one it must be validate
  </code></pre>
  
  <p>Must return invalid if it's a number or any other character besides comma or its length is greater than 2.</p>
  
  <pre><code>AD,12,AN,JP (invalid)
  AAD,12,AN,JP (invalid)
  AA,CC,ANA,JP (invalid)
  AA,#C,AA,JP (invalid)
  </code></pre>