title: Regular Expression first 2 characters either alphabetic or numeric but not combination of both
body: <p>I need a regular expression in PHP to validate a string like: "AB345678" or "12345678". That is, Eight(8) letter string containing first 2 letters as alphabetic or numeric, but not the combination of both, and then the remaining 6 letters numeric.
  I tried to do it by my own but it's not working.</p>
  
  <p>Here is my code:</p>
  
  <pre><code>/^[0-9a-zA-Z]{2}[0-9]{6}$/
  </code></pre>
  
  <p>I'm new to Regex hence need help here.</p>
  
  <p>Thanks in advance.</p>