15.4.5  HIDE 

Controls whether hidden lines are drawn for a 3-d  mesh,  or  whether  one
plot hides the next.  You must specify HIDE for both the plot to be hidden
and the plot that is to hide it.  The plot 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