# File control/DocumentTable/DocumentTable.rb, line 167
  def add_filter
    mask = @entry[:params].mask
    case (mask)
    when NilClass
      mask_value = 'nil'
    when Regexp
      mask_value = 'regexp:' + Rucy::MaskUtil.regexp_to_suffix(mask)
    when String
      mask_value = 'string:' + mask
    else
      raise "unknown mask object: #{mask.inspect}"
    end

    query = {
      'filter' => @entry[:filter_selected],
      'pos' => @src.add_filter_pos.to_s,
      'path' => @entry[:params].path,
      'mask' => mask_value,
      'vhost' => @entry[:params].virtual_host.to_s
    }
    driver = self.driver
    driver.redirect('SetupFilter', query)

    nil
  end