code: function _normalizePrevViewSequence(scrollOffset) {
          var count = 0;
          var normalizedScrollOffset = scrollOffset;
          var normalizeNextPrev = false;
          var node = this._nodes.getStartEnumNode(false);
          while (node) {
              if (!node._invalidated || !node._viewSequence) {
                  break;
              }
              if (normalizeNextPrev) {
                  this._viewSequence = node._viewSequence;
                  normalizedScrollOffset = scrollOffset;
                  normalizeNextPrev = false;
              }
              if ((node.scrollLength === undefined) || node.trueSizeRequested || (scrollOffset < 0)) {
                  break;
              }
              scrollOffset -= node.scrollLength;
              count++;
              if (node.scrollLength) {
                  if (this.options.alignment) {
                      normalizeNextPrev = (scrollOffset >= 0);
                  }
                  else {
                      if (Math.round(scrollOffset) >= 0) {
                          this._viewSequence = node._viewSequence;
                          normalizedScrollOffset = scrollOffset;
                      }
                  }
              }
              node = node._prev;
          }
          return normalizedScrollOffset;
      }
docs: Normalizes the view-sequence node so that the view-sequence is near to 0.