code: function _LayoutCommon_getGroupInfo(groupIndex) {
                      var group = this._site.groupFromIndex(groupIndex),
                          groupInfo = this._groupInfo,
                          margins = this._sizes.containerMargins,
                          adjustedInfo = { enableCellSpanning: false };
  
                      groupInfo = (typeof groupInfo === "function" ? groupInfo(group) : groupInfo);
                      if (groupInfo) {
                          if (groupInfo.enableCellSpanning && (+groupInfo.cellWidth !== groupInfo.cellWidth || +groupInfo.cellHeight !== groupInfo.cellHeight)) {
                              throw new _ErrorFromName("WinJS.UI.GridLayout.GroupInfoResultIsInvalid", strings.groupInfoResultIsInvalid);
                          }
                          adjustedInfo = {
                              enableCellSpanning: !!groupInfo.enableCellSpanning,
                              cellWidth: groupInfo.cellWidth + margins.left + margins.right,
                              cellHeight: groupInfo.cellHeight + margins.top + margins.bottom
                          };
                      }
  
                      return adjustedInfo;
                  }
docs: Can only be called after measuring has been completed