Found another one:
When you use a custom descriptor, the XML output gives you:
<descriptors>
<descriptor name="- Custom Descriptor -"/>
</descriptors>
Of course the data is in the internal file:
<pick thing="pdsOther" index="490" batchindex="245" refcount="0" fieldcount="1" source="pwDescs">
<field id="pdsUserNm" text="My super special descriptor"></field>
</pick>
You just can't get it from the XML unless you parse the summary attribute.