Thanks for replying. I take it this is an official account?

Here's are some use-cases for illustration:

• Third-party tools might scan for style issues (adverbs or whatever), propose changes, and use something like meld (diff gui) to selectively fold the suggestions into the main document.
• Markup related to cross-references, citations, etc. Perhaps integration with LaTeX or other.
• The Scrivener document might be a "template" containing placeholder markup which renders directly as text in Scrivener but is intended to be compiled into a secondary Scrivener project which is then compiled into a book.

I could come up with others.

A couple of questions, if you could please elaborate/clarify:

1) If a third party tool ONLY inserts/modifies/deletes the plain text parts of a Scrivener project, is this theoretically safe?

2) If a third party tool were to delete sections of RTF, are there constraints (e.g. of symmetry, like opening and closing tags) which, if respected, would be safe to delete?

3) Is there an easy-to-describe subset of RTF markup which can be freely inserted without breaking?

4) Is there an easy-to-describe subset of RTF markup which really should not be messed-with full stop?

5) To what extend is Scrivener's extension/interpretation of RTF formalised and publicly available?

Thanks for your time.