title: Replace only the second html tag
body: <p>I want to replace the second <code>h2</code> tag to <code>h3</code> and I hope someone can help me with a replacement regex, or maybe a <code>preg_split</code> - I am not exactly sure.</p>
  
  <p>For example, this:</p>
  
  <pre><code>&lt;h2&gt;My text one&lt;/h2&gt;
  &lt;h2&gt;My text two&lt;/h2&gt;
  text …
  &lt;h2&gt;My text three&lt;/h2&gt;
  </code></pre>
  
  <p>Should become this:</p>
  
  <pre><code>&lt;h2&gt;My text one&lt;/h2&gt;
  &lt;h3&gt;My text two&lt;/h3&gt;
  text …
  &lt;h2&gt;My text three&lt;/h2&gt;
  </code></pre>