def pop(*what)
      if what.length.zero?
        primitive 'pop graphic-context'
      else
        # to_s allows a Symbol to be used instead of a String
        primitive 'pop ' + what.map(&:to_s).join(' ')
      end
    end
def pop(*what)
      if what.length.zero?
        primitive 'pop graphic-context'
      else
        # to_s allows a Symbol to be used instead of a String
        primitive 'pop ' + what.map(&:to_s).join(' ')
      end
    end
Return to the previously-saved set of whatever
 pop('graphic-context') (the default if no arguments)
 pop('defs')
 pop('gradient')
 pop('pattern')