ORA-DM-A-ORDER

*Data Model, Section 3.2 Document order* First para, last sentence 
"There is precisely one document order and it satisfies the following 
constraints...". The preceding definition defines "a document order". 
Note the article "a", implying that there can be more than one. Indeed, 
the constraints acknowledge that there is more than one way to order 
namespace declarations or attributes. So what does "there is precisely 
one document order" mean ?

Perhaps you mean "For a particular implementation of this data model, 
and for each document considered by that implementation, there is 
precisely one document order..."