representing the location in the original
            source which produced this lookup.
        alternates: An ordered dictionary of alternates, mapping glyph names
            to a list of names of alternates.
        lookupflag (int): The lookup's flag
        markFilterSet: Either ``None`` if no mark filtering set is used, or
            an integer representing the filtering set to be used for this
            lookup. If a mark filtering set is provided,
            `LOOKUP_FLAG_USE_MARK_FILTERING_SET` will be set on the lookup's
            flags.
    c