The entry in names that partName names under OPC part-name
equivalence (canonicalPartName), preferring an exact match and
otherwise the first equivalent entry in code-unit order, so the choice
does not depend on how names is ordered; undefined when no entry is
equivalent (#344, #349).
The entry in
namesthatpartNamenames under OPC part-name equivalence (canonicalPartName), preferring an exact match and otherwise the first equivalent entry in code-unit order, so the choice does not depend on hownamesis ordered;undefinedwhen no entry is equivalent (#344, #349).