Insert element in the start or in the middle of a document

I am wondering, would this be a feasible feature to implement? I dug into the code and saw there is an internal _insert_at method implemented; would it be a good idea to expose it as public?

My use case it there is an important metadata table in the document, but if it’s missing, I would like to put it at the very front so the user can be encouraged to fill it out. Appending it at the end makes it much less prominent, but there doesn’t seem to be a good way to “clone” a document with internal trivials intact either (or maybe this is what I actually need?).

I realise I can simply write to the TOML file directly, and re-parse the document again, but that feels more like a hack than a proper solution to me. Plus that approach would be suspect to race conditions IMO because the user may be editing it at the same time.

Start by reading the internal _insert_at method and the document parsing behavior mentioned in the issue. Determine whether a public insertion API or document-cloning approach best preserves existing document trivia, then define the expected behavior for inserting metadata at the front or middle and verify it with focused tests.