Iso10646 encodingLevel and "endian"-ness (Character Set & Language Negotiation)

Sorry if this has been covered, but I don't recall a discussion and didn't see anything in a cursory search of the archives...

If we happened to have a copy of ISO 10646 at hand, we'd probably have our answer, but could anyone comment on the following?

If a Z39.50 client and server negotiate Iso10646 and an encodingLevel of ucs-2, utf-16 or ucs-4 for InternationalStrings, is the byte ordering, or "endian"-ness, of the individual characters specified by the definition of the corresponding ISO 10646 transfer syntax?  (If so, I assume it's typical network byte order.)  Or should Z39.50 InternationalStrings with this negotiation always include initial byte-ordering marks?

Thanks in advance for any information.