Called for every section id present in the file that this reader does not
consume (forward-compat — block-instance sections 7–10, or any future
additive minor-version section). Invoked once per unknown id, before
section bodies are read. Errors thrown from the callback propagate.
Called for every section id present in the file that this reader does not consume (forward-compat — block-instance sections 7–10, or any future additive minor-version section). Invoked once per unknown id, before section bodies are read. Errors thrown from the callback propagate.