Thematic breaks

a

---

b
.
<p>a</p>
<hr />
<p>b</p>

A thematic break is tried before a list item.

- - -
.
<hr />

A formatter writes *** for a rule on a document's first line, where --- would open metadata.

***

# Hi
.
<hr />
<h1 id="hi">Hi</h1>