Additional Characteristics
In order to allow producers of Office Open XML to describe specific contextual conditions under which the document was created, additional characteristics can be provided within the Additional Characteristics part using the syntax defined below.
The set of additional characteristics is designed to be an extensible list, and can provide a consumer with more information on how to interpret the file. This Standard defines one set of characteristics; however, additional grammars can be created and associated with a unique URI via the @vocabulary
attribute.