{% comment %}
The "download the full book" link, as its own partial so an app that knows
more than core does can offer something better.

parody_web_annotate shadows it to add a copy carrying every section's notes —
what a student prints to revise from, or to take into an exam.

Context: book, book_pdf_url, and on section pages the section context too.
{% endcomment %}
{% if book_pdf_url %}<a href="{{ book_pdf_url }}">Download the full book</a>{% endif %}