def default_line_item(params)
          html =  "#{indent*1}<tr>\n"
          html << "#{indent*2}<td class=\"tax-point\">#{   params[:line_tax_point]   }</td>\n" if options[:tax_point_column]
          html << "#{indent*2}<td class=\"quantity\">#{    params[:line_quantity]    }</td>\n" if options[:quantity_column]
          html << "#{indent*2}<td class=\"description\">#{ params[:line_description] }</td>\n" if options[:description_column]