[Feature Request] cross-book content sharing

[iampi31415]

Problem

Different books tend to repeat much of their content across mdbooks.

For example, all the great embedded-rust books. After all all need to show how to set up Rust.

They then evolve independently, and each one loses knowledge that was added to another one, without a way to opt-in to updates.

Proposed Solution

As an example, Wikipedia they has sections coming from other articles.

It would be awesome if one could do this:

1. Directly link a remote markdown page in SUMMARY.md using, for example:

   <!--SUMMARY.md-->
   # Summary  
   - [Same Chapter](https://www.github.com/otherbook/path.to.md)
   <!--probably the raw version-->
   - [Contributing](https://raw.githubusercontent.com/rust-lang/mdBook/refs/heads/master/CONTRIBUTING.html)

2. The Edit on Github link in the page should direct to that file/url, then users would always edit or try to edit an upstream.

Notes

Ideally, some version number of the file (maybe the commit hash) should be allowed so that content does not change unexpectedly.

Maybe there is some pre-processor that does this, I have not seen one.

I am aware this is quite a stretch, but it's just an idea.

[iampi31415]

There is one: https://github.com/phoenixr-codes/mdbook-webinclude, which works analogous to include and has a the good name webinclude. Though I don't quite like to use AI-generated code.

I think it must be easy to add a fetch though, using handlebars?
iframes wouldn't be so good I suppose, since I'd like to use specific source files (from a commit.)