code: def rotation=(val)
  			permissible = [0, 90, 180, 270]
  			fail ArgumentError, "invalid rotation, permissible: #{permissible.join(', ')}" unless permissible.include?(val % 360)
  			@rotation = val % 360
  			push_all_pixels
  		end
docs: Set rotation of the Unicorn HAT to +val+
  
   Permissible values for rotation are [0, 90, 180, 270] (mod 360).
  
   You still have to call +show+ to make the changes visible.