Write a document body

This is the one route in the API that writes one: the drive item itself carries no body. content is GitHub-Flavored Markdown, an empty body is rejected and any key other than content and mode is a 422. By default mode is replace: the Markdown you send becomes the whole document, which overwrites whatever somebody else typed since your last read and discards, permanently, the text colours, highlights, alignment and @mentions Markdown cannot express; read ?include=content_html on the document first if it may contain them. With mode: append the Markdown is added after the existing body and nothing already there is touched, which is the safe way to add notes to a shared document. The write goes through the live collaboration session, so anyone with the document open sees it immediately; if the collaboration server refuses the content, or is unavailable while the document is under collaborative editing, the write is refused with a 422 on /content rather than silently lost. Send If-Match with the ETag from your last read to detect a concurrent edit, which answers 412. Treat it as best-effort only: this resource carries no revision number and updated_at is second-precision, so two writes inside the same second are indistinguishable. The declared permission is project_drive::create (editing is part of the create permission); the other three drive prefixes apply by the owning item's owner type, and the record rule is edit access on that item. Note that the owning item being archived does not block this write, even though the item itself then reads as 404 without trashed=with; restore the item first if you want plnnrly and the API to agree.