Allow the same document in multiple chapters/sections

[davidvandebunte]

Context

In large Jupyter Books, it would be helpful to include the same content (e.g. an .md file) in multiple places in the TOC.

One use case for this is when you want to provide draft articles in a separate area (e.g. lower in the TOC) but still anchored off of "complete" articles. The complete articles would show up in both sections.

Another use case would be to simply reuse content, perhaps to refresh a reader on a topic they may have not seen in some time, or to introduce a reader to a much earlier prerequisite that they may have missed because they "jumped" into the middle of the book. See e.g. OpenLogicProject/OpenLogic: An open-source, customizable intermediate logic textbook; the content subdirectory in this project takes this to the extreme in the sense of only providing "sections" of a chapter as individual files that users can then assemble into different books.

Proposal

Hopefully this is as simple as removing a restriction, making the code simpler rather than more complex.

Tasks and updates

No response