15.40.7  HIDE 

Controls whether hidden lines are drawn for a 3-d  mesh,  or  whether  one
histogram hides the next.  You must specify HIDE for both the histogram to
be hidden and the histogram that is to hide it.  The  histogram  which  is
drawn  first  will  hide the second one.  HIDE=OFF draws the hidden lines,
while HIDE=ON omits them.
(Default:HIDE=ON for mesh, HIDE=OFF for data)

                                  example
Assume  you  have 2 data sets where you want set 1 to hide elements in set
2.  Also you would like to fill data set 2.
     TD:JOIN SET=1 HIDE
     TD:JOINS SET=2 HIDE FILL

You  can  produce a drawing of a mesh with hidden lines as dotted lines by
doing the histogram twice:
     TD:HISTOGRAM
     TD:HISTOGRAM HIDE=OFF DOTTED