docs: function getChildVariable() {
              var indexArr = this.options.rowIndex.split('.');
              var lastIndex = indexArr[indexArr.length - 1];
              var fieldArr = this.options.field.split('.');
              var lastField = fieldArr[fieldArr.length - 1];
              var lastDataTable = this.dataModel;
              var lastRow = null;
  
              for (var i = 0; i < fieldArr.length; i++) {
                  lastRow = lastDataTable.getRow(indexArr[i]);
                  if (!lastRow) break;
                  if (i < fieldArr.length - 1) {
                      lastDataTable = lastRow.getValue(fieldArr[i]);
                  }
              }
              return {
                  lastField: lastField,
                  lastIndex: lastIndex,
                  lastDataTable: lastDataTable,
                  lastRow: lastRow
              };
          }