- Adjust transcript shortcodes to also support <audio> elements.
- Add audio element shortcode based on <picture> shortcode
- Make <audio> elements match container width.
- Add a11y metadata to transcribed images to communicate the presence of
a transcript
- Fix relative urls in navigation: make them absolute urls, so that the
parsed navigation elements have the correct destinations.
This also switches image transcripts from a section with a heading to a
div with an ARIA label. That should reduce duplication between the
<summary> content and the heading while still being semantically sound.
- Identify the transcript with a subheading, ending in a period so that
the aria-description separates the identifier from the concept.
- Put the transcript in a <section>
- Snuck in a trivial syntax fix for the generator element.
