is not published by M$. (there might be an exeption for some unusual very complex word documents not fully understandable by openoffice, but from my experience this is only a very tiny proportion of word documents using some special feature like macros, etc.).Your last sentence shows that the specification is not public. That is all that is required to keep it from being Transparent. Having a tool that partially implements the spec does not completely document the spec.
The whole specification is indeed not public. What I claim is that a document using only word features fully understandable by openoffice might be considered as trandsparent since it use only spec available to the public: the subset of word fully understandable by openoffice is public. If a document use features that are not available to the public it is indeed not transparent. But there are very few such documents.
Olive