title: Ignore html tags in preg_replace
body: <p>How do I <strong>ignore html tags</strong> in this preg_replace.
  I have a foreach function for a search, so if someone searches for "apple span" the preg_replace also applies a span to the span and the html breaks:</p>
  
  <pre><code>preg_replace("/($keyword)/i","&lt;span class=\"search_hightlight\"&gt;$1&lt;/span&gt;",$str);
  </code></pre>
  
  <p>Thanks in advance!</p>