luce/spec/extensions/fenced_code_blocks.unit

>>> without an optional language identifier
```
code
```

<<<
<pre><code>code
</code></pre>
>>> with an optional language identifier
```dart
code
```

<<<
<pre><code class="language-dart">code
</code></pre>
>>> escape HTML characters
```
<&>
```

<<<
<pre><code>&lt;&amp;&gt;
</code></pre>
>>> Pandoc style without language identifier
~~~~~
code
~~~~~

<<<
<pre><code>code
</code></pre>
>>> Pandoc style with language identifier
~~~~~dart
code
~~~~~

<<<
<pre><code class="language-dart">code
</code></pre>
>>> Pandoc style with inner tildes row
~~~~~
~~~
code
~~~
~~~~~

<<<
<pre><code>~~~
code
~~~
</code></pre>