title: PHP using preg_match or regex as value for array_search or the key for array_keys_exist
body: <p>I was wondering if it was possible to use regex or <code>preg_match()</code> in <code>array_seach()</code> or <code>array_keys_exist</code>?</p>
  
  <p>ie.
  <code>array_keys_exist($array,"^\d+$")</code> to match all keys that are solely numeric characters</p>