title: preg_match pattern for steamid
body: <p>what is the correct pattern to check string which contains only numbers like this <code>76561197960265728</code>?</p>
  
  <p>I've tried to check with <code>var_dump(preg_match('/(\d+)/', '76561197960265728'));</code> but it returns true no matter if there will be letters or symbols in string or not.</p>