A 2d group mask enables to compute and blend some masks together during an intermediary rendering pass.
				Once masks are grouped, the overall 
Opacity of the group can be modulated or inverted.
                    A 2d group mask can be creating by selecting 
                    2D TextureMask
                    Define a 2D Mask applicable on any 2D Renderer or 2D Modifier
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                     and pressing the "Create Group" shortcut: 
                    
                      [CTRL] + [SHIFT] + [G]
                    .
  
