This rule is triggered when fenced code blocks are either not preceded or not
followed by a blank line:

````markdown
Some text
```
Code block
```

```
Another code block
```
Some more text
````

To fix this, ensure that all fenced code blocks have a blank line both before
and after (except where the block is at the beginning or end of the document):

````markdown
Some text

```
Code block
```

```
Another code block
```

Some more text
````

Set the `list_items` parameter to `false` to disable this rule for list items.
Disabling this behavior for lists can be useful if it is necessary to create a
[tight](https://spec.commonmark.org/0.29/#tight) list containing a code fence.

Rationale: Aside from aesthetic reasons, some parsers, including kramdown, will
not parse fenced code blocks that don't have blank lines before and after them.