[DFDL-WG] Alternate Initiators?

Consider the following IMF headers: Message-ID: <CACQ76nh2VDypuwm1aHc1-s8ZmmyXg8XEosS6af6yurkVdT+8QQ@mail.gmail.com> Message-Id: <208E8372-A9D9-468A-9B4B-BD97ED28F64C@garriss.org> Notice the difference: Message-ID: vs Message-Id: Per the RFC, only the first is legal, but both are used in practice, and we'd like to allow either. In our DFDL schema, "Message-ID" is an initiator, but suddenly we have two alternate initiators for the same element. How we model this in DFDL? TIA