# File lib/loofah/scrubber.rb, line 64
    def initialize(options = {}, &block)
      direction = options[:direction] || :top_down
      unless [:top_down, :bottom_up].include?(direction)
        raise ArgumentError, "direction #{direction} must be one of :top_down or :bottom_up" 
      end
      @direction, @block = direction, block
    end