One pattern I often see is namespaces with different versions, but an xpath query would work for any version.  For example, I would like to make an xpath query that searches any of the 5 versions of DDMS.

urn:us:mil:ces:metadata:ddms:4
urn:us:mil:ces:metadata:ddms:5


Versioning of namespaces is nearly always a mistake, but it's a rather common mistake.

Michael Kay
Saxonica