Optically, this inner differentiation led on to super-ordinate patterns.
“It is a combination of multiple grids. One grid is : formed by the regular alignment of small squares in rows and columns. This grid seems to lie in the foreground with another grid as background, formed by the overall picture behind the individual squares or ‘windows’ within which mayor may not be a grid or parts of a grid. The small squares are either blank or contain one or more line elements arranged in an arbitrary order.” (Coqart 1980/81, p. 58) 5