Invalid HTML being generated.

On this page:

https://docs.ruby-lang.org/en/2.7.0/Array.html

```
<p>Items can be added to the end of an array by using either <a href="Array.html#method-i-push"><code>push</code></a> or <a href="Array.html#method-i-3C-3C"><code><<</code></a></p>
```

Note `<code><<</code>` is invalid HTML.

I saw this on some other pages.

Not all output is being escaped.