code: function(options) {
          var thead = $('<thead><tr></tr></thead><tbody></tbody>'),
              column = options.column,
              columnCount = column.length;
  
          this.rowSpan = 1;
  
          for (var i = 0; i < columnCount; i++) {
              var col = column[i];
  
              if (typeof col.visible !== 'undefined' && !col.visible) {
                  continue;
              }
  
              if (!$.isArray(col.content)) {
                  col.content = [col.content];
              }
              if (col.content.length > this.rowSpan) {
                  this.rowSpan = col.content.length;
              }
  
              var th = $('<th nowrap></th>').attr({
                  width: col.width,
                  field: col.field
              });
              if (options.flexible) {
                  th.removeAttr('nowrap width');
              }
  
              var title = (col.escapeTitle === false) ? col.title : escapeHTML(col.title);
              if (col.sortable) {
                  var wrap = $('<div class="sortable"></div>').html(title);
                  if (col.currentSort) {
                      wrap.attr(col.currentSort, '');
                  }
                  title = wrap.prop('outerHTML');
              }
  
              thead.find('tr').append(th.html(title).prop('outerHTML'));
          }
  
          return thead.prop('outerHTML');
      }
docs: 创建 thead
  @param {Object} options 参数
  @return {String}
  @private