I'm not sure how this was implemented, but I'm trying to do the same thing and in the context of a "Select In Field" button, neither this
work at all in the button. Are you sure this is exactly what must be pasted in the search string area? I've got "Select In Field" for the button, and "=add_date" in the Field area (no quotations). Any help? I'd rather not post a duplicate question if I can avoid it.