def default_line_items_header(params)
          html =  "#{indent*1}<tr>\n"
          html << "#{indent*2}<th class=\"tax-point\">#{   params[:line_tax_point_label]   }</th>\n" if options[:tax_point_column]
          html << "#{indent*2}<th class=\"quantity\">#{    params[:line_quantity_label]    }</th>\n" if options[:quantity_column]
          html << "#{indent*2}<th class=\"description\">#{ params[:line_description_label] }</th>\n" if options[:description_column]