const bool needs_quotes = (
    was_quoted
    ||
    (
        ( ! s.is_number())
        &&
        (
            // has leading whitespace
            s.begins_with_any(" \n\t\r")
            ||
            // looks like reference or anchor or would be treated as a directive
            s.begins_with_any("*&%")
            ||
            s.begins_with("<<")
            ||
            // has trailing whitespace
            s.ends_with_any(" \n\t\r")
            ||
            // has special chars
            (s.first_of("#:-?,\n{}[]'\"") != npos)
        )
    )
);