Define preferred partition method for complete sets of part values

6.1.3 Part
...
Note: The attributes of Part are also referred to as <glossary ref> ‘partition keys’</glossary ref> .

6.1.3.3 Multiple Part Elements in One Resource
A ResourceSet MAY contain one or more Resource elements that MAY respectively contain zero or more Part elements.
Each Resource represents one entity, regardless of the number of Part elements. If a Resource contains more than one
Part element, this Resource is applicable to any of the contained Part elements. For instance a set of plates for a versioned
CMYK sheet with black change for English and French versions could have 5 plates. The Cyan, Magenta and Yellow would
each contain 2 Part elements with both English and French whereas the two individual Resource elements for the Black
plates would contain the respective individual @PartVersion.
The Part elements SHOULD be as sparsely defined as possible.
Example: A sheet typically has both a front and a back side. If a partition applies to the entire sheet, the resource SHOULD be specified as:
<Resource>
<Part SheetName="Sheet1"/>
</Resource>
and not as:
<Resource>
<Part SheetName="Sheet1" Side="Front"/>
<Part SheetName="Sheet1" Side="Back"/>
</Resource>