code: int fillBackwardFrom0(int itemIndex, double upTo) {
          double min = orientation.minY(positioner.getVisibleCell(itemIndex));
          int i = itemIndex;
          while(min > upTo && i > 0) {
              --i;
              C c = positioner.placeEndFromStart(i, min);
              min = orientation.minY(c);
          }
          return i;
      }
docs: does not re-place the anchor cell