Headers and footers are currently read-only in gog docs — they surface in raw / structure output but there is no way to create, populate, or delete them. The four Docs API requests exist:

• createHeader / createFooter (with a SectionBreakLocation or default type)
• deleteHeader / deleteFooter

Once a header/footer segment exists, its body is addressable by segmentId, so populating it can reuse the existing text/insert path with a --segment selector.

Proposed:

gog docs header create <docId> [--type DEFAULT|FIRST_PAGE] [--text <content>]
gog docs header delete <docId> --id <headerId>
gog docs footer create <docId> ... / footer delete ...

and a --segment header:<id>|footer:<id> selector on insert / format so the body content can be written and styled the same way as the main body. This closes the last read-only-only structural surface; header/footer authoring currently has no path at all short of editing in the UI.

Ref: documents.batchUpdate CreateHeaderRequest, CreateFooterRequest, DeleteHeaderRequest, DeleteFooterRequest.