The kind of data.
OptionalmodalityDICOM Modality (0008,0060), when the header says.
OptionalreaderThe version of the reader that wrote them: a newer reader reads a feed again rather than trust an older one's answer.
OptionalreasonWhy the format is unknown or other, in words.
OptionalseriesDICOM SeriesDescription (0008,103E), when it says.
OptionalsourceThe feed whose output this feed's data is, when it began from another feed's work.
What a feed's data is, read once from the first file its root produced: the format, and for DICOM the modality and series description.