docs: function (position, size, base) {
              var viewportSize = this._getViewportSize();
              var documentScroll = this._getDocumentScroll(base);
  
              if (position.top < documentScroll.scrollTop || position.left < documentScroll.scrollLeft
                      || position.top + size.height > documentScroll.scrollTop + viewportSize.height
                      || position.left + size.width > documentScroll.scrollLeft + viewportSize.width) {
                  return false;
              } else {
                  return true;
              }
          }