title: PHP (Regex) Check if a string contains at least 4 digits + 2 letters
body: <p>I would check a string if contains <strong>at least</strong>:</p>
  
  <p>2 letters (a-z) CASE INSENSITIVE
  4 digits (0-9)</p>
  
  <p>the order is not important. It could be <strong>a1234b</strong>, <strong>abcd1234</strong>, <strong>4444aa</strong> etc etc.</p>
  
  <p>My actual regex is </p>
  
  <pre><code>if (preg_match("/[a-z][^a-z]*[a-z]*[0-9]/i",$string)) {
  echo 'secure';
  $continue = true;
  }
  </code></pre>
  
  <p>and it <strong>doesn't</strong> function if string start with a digit. Thank you</p>