title: PHP preg_match $offset option confusion
body: <p>in php.net preg_match page, it says</p>
  
  <blockquote>
    <p>Note:
    Using offset is not equivalent to passing substr($subject, $offset) to >preg_match() in place of the subject string, because pattern can contain >assertions such as ^, $ or (?&lt;=x).  </p>
  </blockquote>
  
  <p><a href="http://php.net/manual/en/function.preg-match.php" rel="nofollow noreferrer">php.net</a></p>
  
  <p>Does this mean the <strong>offset</strong> option will be ignored if there are assertions in the pattern.
  How exactly assertions affect subject strings</p>