header, ignoring that it is within begin_example. See below
I am using org-mode version 9.0.3, under emacs-25.
<div id="content">
<div id="table-of-contents">
<h2>Table of Contents</h2>
<div id="text-table-of-contents">
<ul>
<li><a href="#org4937d33">1. Example</a></li>
<li><a href="#org774a613">2. hello world 2</a></li>
</ul>
</div>
</div>
<div id="outline-container-org4937d33" class="outline-2">
<h2 id="org4937d33"><span class="section-number-2">1</span> Example</h2>
<div class="outline-text-2" id="text-1">
<pre class="example">
hello world 1
</pre>
<p>
#+begin<sub>example</sub>
</p>
</div>
</div>
<div id="outline-container-org774a613" class="outline-2">
<h2 id="org774a613"><span class="section-number-2">2</span> hello world 2</h2>
<div class="outline-text-2" id="text-2">
<p>
#+end<sub>example</sub>
</p>
</div>
</div>
</div>