code: function(options) {
          var sum = $('<tr class="sum"></tr>'),
              column = options.column,
              columnCount = column.length;
  
          if (options.selectable) {
              sum.append('<td width="24"></td>');
          }
  
          for (var i = 0; i < columnCount; i++) {
              var col = column[i];
  
              if (typeof col.visible !== 'undefined' && !col.visible) {
                  continue;
              }
  
              var td = $('<td></td>').attr({
                  align: col.align,
                  width: col.width,
                  class: col.customClass
              });
  
              if (options.flexible) {
                  td.removeAttr('width');
              }
  
              var content = col.footContent ? col.footContent.call(this, col.field).toString() : '';
              td.html((col.escapeContent === false) ? content : escapeHTML(content)).appendTo(sum);
          }
  
          return sum.prop('outerHTML');
      }
docs: 创建总计行
  @param {Object} options 参数
  @return {String}
  @private