# File lib_core/rucy/document.rb, line 205
    def set_filter_option(filter_name, opt_name, opt_value)
      unless (@filter_map.include? filter_name) then
        raise "not found a filter: #{filter_name.inspect}"
      end
      @filter_map[filter_name].set_filter_option(opt_name, opt_value)
      nil
    end