+@code{dataset} is the name of the dataset analyzed to produce the
+output, e.g.@: @code{DataSet1}, and @code{datafile} the name of the
+file it was read from, e.g.@: @file{C:\Users\foo\bar.sav}. The latter
+is sometimes the empty string.
+
+@code{date} is a date, as seconds since the epoch, i.e.@: since
+January 1, 1970. Pivot tables within an SPV files often have dates a
+few minutes apart, so this is probably a creation date for the tables
+rather than for the file.
+
+Sometimes @code{dataset}, @code{datafile}, and @code{date} are present
+and other times they are absent. The reader can distinguish by
+assuming that they are present and then checking whether the
+presumptive @code{dataset} contains a null byte (a valid string never
+will).
+