The Batch dialog has a File Name choice for a Data Sets source, starting
with File + Number (`source001`), as well as File + Data Set Name
(`source_Alpha`) and Data Set Name (`Alpha`). `action.batch` takes it as
`datasetFileNaming`; a call without it keeps File + Data Set Name, and a
folder source ignores it. An unknown value is an error.
A data set output whose name already exists in the destination folder
now takes the next free `-2`, `-3` suffix instead of replacing the file,
and a Windows device name under Data Set Name gets a trailing `-`.
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