An inline atom drawn gray as ‹label›: a click selects the whole field,
typing replaces it, Tab/Shift-Tab jump between fields. Exports to ODF
<text:placeholder> (PLH sentinel U+E022) and a DOCX w:sdt content
control tagged edentext-placeholder; both importers read it back, the
export-minted gray stripped. Covered in roundtrip Leg 31 + fuzzDoc.