MS Office XML format not so clear

Yesterday, in a meeting at school, I could clearly see what could prevent us
to consider MS Office XML file as open.

• There is a processing directive at the beginning of the Word document
  saying: “it’s a word document”. This could be interpreted by the XML
  parser to do what it want’s wihtout we know it.
• To our surprise, there are some XML namespaces where the URN is
  no. This means obviously that the format is not fully known by a
  customer.

I have an answer now for people saying me that MS Office XML is open…
XML doesn’t necessary mean open !

(Post originally written by Cedric Bosdonnat on the old Nuxeo blogs.)