Messed up the line break.

“[…] when you add a role to an element you change its nature to
assistive technologies. So because doc-footnote isn't a list item role,
it would strip the li tag of its list item nature and turn it into
something more like a div or a p tag. That breaks the list semantics for
AT users, so they'd no longer be able to access the list as though it
were a list.”
<https://github.com/w3c/epubcheck/issues/1018#issuecomment-809376951>

replaced `<span><aside>` with `<li>`.

‘E-books’ is enough.

Only wrap the text that the user is supposed to enter in
<code>-tags. Before it was easy to misinterpret and enter extra spaces.

They are case insensitive anyway, might as well write them right.