     y = @_top_from_row_nr me, row_nr
     yield [ 'tex', "\\draw[sDebugCellgrid] (#{left},#{y}) -- (#{right},#{y});\n", ]
   #.........................................................................................................
+  yield [ 'tex', "\\end{scope}\n", ]
+  #.........................................................................................................
   yield return
 
 #-----------------------------------------------------------------------------------------------------------
 @_walk_debug_fieldgrid_events = ( me ) ->
   unless @_should_debug me
     yield return
+  #.........................................................................................................
+  yield [ 'tex', "\\begin{scope}[on background layer]\n", ]
   #.........................................................................................................
   for designation, d of me.field_dimensions
     ### TAINT use fixed size like 1mm ###

                 + " -- (#{right},#{bottom});", ]
    yield [ 'tex', "\n", ]
  #.........................................................................................................
  yield return

#-----------------------------------------------------------------------------------------------------------

  unless @_should_debug me
    yield return
  #.........................................................................................................
  yield [ 'tex', "\\begin{scope}[on background layer]\n", ]
  #.........................................................................................................
  ### TAINT use fixed size like 1mm ###
  top       = ( @_top_from_row_nr     me, 1             ) - 3
  bottom    = ( @_bottom_from_row_nr  me, me.gridheight ) + 3
