pulldown-cmark-to-cmark is a really handy crate for doing things like writing mdBook preprocessors, which I have been doing a bit of while working on The Rust Programming Language, but I have noticed that it is challenging for that crate to match the input precisely, and there are a fair number of subtle bugs that are (a) difficult for them to fix and therefore (b) require special handling in preprocessors using it, e.g. to manually re-insert newlines.

This is not a bug report, though, as I don’t think that kind of round-tripping was part of the design here! Rather, it is intended to start a discussion, on two axes:

• Is supporting that kind of round-tripping desirable?
• If so, what changes would be required to support it?
  • Maintaining original source spans (e.g. Provide Tag and Event source locations. #725)—but then how do you integrate that info when you insert new Events into a stream of Events (e.g. when rewriting in a preprocessor, extending behavior, etc.)?
  • Including list item types?
  • Including line wrapping for blockquotes?
  • etc.: I am sure there are a bunch of others

I think there are probably a bunch of open design questions there beyond just what would have to change, so, as I said: opening this for discussion and not assuming it is something the library should do.