TVBOX is used to show the boundaries of a box on the television. You can show a box defined in the command BOX, or show a region centered on a given point. You must specify EITHER the box number with BOX=, or the size AND the location with SIZE= and PIX=.
There must be an image already in the TV for this command to work. The displayed box will be clipped at the edge of the image if the box extends over the bounds of the image.