As a Wikisource user, I don't want the download button to show on subpages, so that I don't encounter the situation of attempting to download a whole book and yet only download a section of a book.
Background: The download button (added in T271869) should only be shown on top-level pages. Two magic words should be added:
- __WIKISOURCEDOWNLOAD__ to force the display of the button (e.g. on work title subpages for multi-work volumes); and
- __NOWIKISOURCEDOWNLOAD__ to prevent it (e.g. on disambiguation pages).
- Don't show download button on subpages
- Opt-out for top-level pages