This flag may be used to indicate that the layout of the answer array is the same as that of the data array. The main limitation is that it does not support drag/drop or multi-selection. (It may be extended in the future to the more general case). The current primary motivation is to permit the use of same array (or identically formatted ones) for both the answer and data in trees involving checkboxes. (You were already allowed to use the same array for both parameters, but it wouldn't have worked with checkboxes due to the normal rule requiring checkboxes to be placed at the start of each row in the answer array.)
The flag is set automatically when you pass the same variable for both the answer and data parameters.
History
2011 September, A-Shell 5.1.1231: XTF2_ANSEQDATA can now be used even when the array contains fields that are not editable, or possibly not even defined. Previously, if the array width didn't match the sum of the widths of the editable columns, the data layout got out of sync with the tree layout.
2011 January, A-Shell 5.1.1202: Flag to A-Shell