_shiftBlock(parentId, diff) {
    const progress = {};
    const shifter = (parentId) => {
      if (progress[parentId]) {
        return;
      }
      progress[parentId] = true;
      this.direction.shift(parentId, diff);

      const childRef = this.hierarchical.childrenReference[parentId];
      if (childRef !== undefined) {
        for (let i = 0; i < childRef.length; i++) {
          shifter(childRef[i]);
        }
      }
    };
    shifter(parentId);
  }
Shift a branch a certain distance
@param {Node.id} parentId
@param {number} diff
@private