gcardosi pointed out that as of PMML 4.2 "predicted" MiningFields can be taken to be synonmyous with "target" MiningFields. Therefore the rule we have in selection of OutputField targets can be widened.

We also need to check on gcardosi comment regarding "targetField" only being mandatory for OutputField's with feature "predictedValue" as I was unable to find mention of this in the specification.

It may refer also to a "predicted" MiningField (my understanding is they are synonymous). Beside that, OutputField target may also refer to other field described in Targets element (not supported by the UI). Last, I'm not sure about "targetField is required if the model has multiple target fields.": my understanding is that is true only for OutputField's with feature="predictedValue".