code: function lastRefreshInsertionPoint() {
                      var slotNext = refreshEnd;
                      while (!slotNext.firstInSequence) {
                          slotNext = slotNext.prev;
  
                          if (slotNext === refreshStart) {
                              return null;
                          }
                      }
  
                      return slotNext;
                  }
docs: Returns the slot after the last insertion point between sequences