Expl Cols

Key Expl Cols of function Parse in Setrefers to an optional 1D-array of - not necessarily increasing - integers starting with 1.
They define the columns in the final filtered set that correspond to the N explicit types supplied in Expl Types
Note, a non-index-based column specification may be alternatively defined through the optional entry Expl Top Labels
If omitted, the supplied N explicit types apply on the first (leftmost) N columns of the final filtered set in sequence.
If suppled, the number of integers should equal N.

For example, assume the entry Expl Types defines the two explicit types Integer and Date
Then assume the entry here contains the two integers 1 and 3.
This would mean that the first explicit type Integer applies on the first column and the second explicit type Date applies on the third column of the final filtered set.