Same as for other newsgroups. The protocol was originally specified in RFC
977 (based on RTF 850), and subsequently in RFC 3977. There are other RFCs
defining NNTP extensions.
(and a few more for MSWord)
news://msnews.microsoft.com/microsoft.public.word.docmanagement
news://msnews.microsoft.com/microsoft.public.word.word97vba
news://msnews.microsoft.com/microsoft.public.word.newusers
news://msnews.microsoft.com/microsoft.public.word.pagelayout
news://msnews.microsoft.com/microsoft.public.word.vba.addins
news://msnews.microsoft.com/microsoft.public.word.vba.beginners
news://msnews.microsoft.com/microsoft.public.word.vba.customization
news://msnews.microsoft.com/microsoft.public.word.vba.general
news://msnews.microsoft.com/microsoft.public.word.vba.userforms
news://msnews.microsoft.com/microsoft.public.word.word6-7macros