This corresponds to the X column in the foo table of the XFoo production database. Unfortunately, it does not appear to be actually used for anything in that database. They do not have consistency checking on the data, and the sole purpose of the field, as explained by the documentation, is to appear under a specific heading. Big freaking whoop. They do have a suggestion for what you can do with the field, and, in an odd coincidence, I have a suggestion for what they could do with this field.