Strange ?proprietary? inclusions in MSOfficeXML?
While reading an article from Doug Mahugh on MSOfficeXML packaging/file structure, I noticed a troubling section entitled "Alternative Format Import Parts: AFChunks". His description makes them sound like they are necessary for backward compatiblity, but that they will not be fully documented.
It also talks about "conforming" producers and consumers, and that a "conforming" producer will never create a file with these. I can't imagine that any of Microsoft's own producers will be "non-conforming", so who would use it?
This just seems like a real can of worms where implementations can radically differ and cause conversion and preservation to fail.
The full quote, so you can draw your own conclusions:
During the transition from binary document formats to Office Open XML, there are going to be a lot of hybrid documents that contain embedded sections and objects that are in older formats: HTML, RTF, earlier versions of WordProcessingML, and so on. To allow for this inevitable complexity, the Office Open XML formats allow for alternative format chunks that may be in one of these older formats.
AFChunks are handled in essentially the same manner as embedded objects. The document part contains a relationship tag, and the separate definition of that relationship tag in the corresponding .rels part tells where to get the chunk.
Note that the intent of AFChunks is for support of the migration of content to Office Open XML. A conforming consumer should read AFChunks and dynamically insert them in the appropriate places as defined by the relationships, but a conforming producer of Office Open XML should never write AFChunks in its output. See section 10.3.1, "Alternative Format Import part," for more information.
File Formats: MSOfficeXML