Javadoc
Like
#retract(), this removes the "on" cells that are 4-way-adjacent to any "off" cell, but unlike that
method it keeps a fraction of those surface cells, quasi-randomly selecting them. This can be thought of as
running
#surface() on a copy of this GreasedRegion, running
#quasiRandomRegion(double) on that
surface with the given fractionKept, taking the original GreasedRegion and removing its whole surface with
#retract(), then inserting the quasi-randomly-removed surface into this GreasedRegion to replace its
surface with a randomly "damaged" one.