<h1>h1</h1>
<h2>h2</h2>
<h3>h3</h3>
<h4>h4</h4>
<h5>h5</h5>
<h6>h6</h6>
<p>####### not a heading</p>
<p>#not a heading</p>
<h1>closed h1</h1>
<h1></h1>
<h2></h2>
<h1># of levels</h1>
<h1># of levels #</h1>