I've been asked several times, why the trellis variable (column) isn't part of the legend in DXP 1.1. One of the big usability issues is that you cannot see and delete trellis variables/columns to the "X"-drop target - which would be a major enhancement to the usability of trellis (i.e, the color variable is remove simply by dragging onto the red "X" on the drop target.)
