Definition lists are just like ordinary bullet lists, but with
`:` as the marker instead of `-`, `+`, or `*`.  The first
paragraph of the list item is interpreted as the term, and
the rest as the definition.

```
: apple

  red fruit
: banana

  yellow fruit
.
<dl>
<dt>apple</dt>
<dd>
red fruit
</dd>
<dt>banana</dt>
<dd>
yellow fruit
</dd>
</dl>
```

Loose:

```
: apple

  red fruit

: banana

  yellow fruit
.
<dl>
<dt>apple</dt>
<dd>
<p>red fruit</p>
</dd>
<dt>banana</dt>
<dd>
<p>yellow fruit</p>
</dd>
</dl>
```

```
: apple
 fruit

  Paragraph one

  Paragraph two

  - sub
  - list

: orange
.
<dl>
<dt>apple
fruit</dt>
<dd>
<p>Paragraph one</p>
<p>Paragraph two</p>
<ul>
<li>
sub
</li>
<li>
list
</li>
</ul>
</dd>
<dt>orange</dt>
<dd>
</dd>
</dl>
```

````
: ```
  ok
  ```
.
<dl>
<dt></dt>
<dd>
<pre><code>ok
</code></pre>
</dd>
</dl>
````