ORA-DM-ORDERTOTAL

*Data Model, Section 3.2 Document order*
The first paragraph says that a document order is total.
The last two paragraphs broaden the discussion to include order between 
nodes in different documents, or not in a document at all.
Is it intended that the ordering in the latter two paragraphs is total? 
Or could a conforming implementation simply say, "I choose not to define 
an ordering between nodes in different documents, or between nodes not 
in any document. My ordering of these things is the trivial ordering, 
the one which such things simply have no ordering."?

Put another way, is there anything that breaks if an implementation is 
not able to place a collection of free-standing nodes into a stable order?