Currently the generated `<pre>` element isn't fully accessible as it can't be focused by keyboard users.
To make this fully accessible, the attribute `tabindex="0"` should be added to the `<pre>` tag.
Closes#7194
This commit adds the fast and CommonMark compliant Goldmark as the new default markdown handler in Hugo.
If you want to continue using BlackFriday as the default for md/markdown extensions, you can use this configuration:
```toml
[markup]
defaultMarkdownHandler="blackfriday"
```
Fixes#5963Fixes#1778Fixes#6355
