code: function autoScroll(tree, event) {
  		var spOfs,
  			scrollTop,
  			delta,
  			dndOpts = tree.options.dnd5,
  			sp = tree.$scrollParent[0],
  			sensitivity = dndOpts.scrollSensitivity,
  			speed = dndOpts.scrollSpeed,
  			scrolled = 0;
  
  		if (sp !== document && sp.tagName !== "HTML") {
  			spOfs = tree.$scrollParent.offset();
  			scrollTop = sp.scrollTop;
  			if (spOfs.top + sp.offsetHeight - event.pageY < sensitivity) {
  				delta =
  					sp.scrollHeight -
  					tree.$scrollParent.innerHeight() -
  					scrollTop;
  				// console.log ("sp.offsetHeight: " + sp.offsetHeight
  				// 	+ ", spOfs.top: " + spOfs.top
  				// 	+ ", scrollTop: " + scrollTop
  				// 	+ ", innerHeight: " + tree.$scrollParent.innerHeight()
  				// 	+ ", scrollHeight: " + sp.scrollHeight
  				// 	+ ", delta: " + delta
  				// 	);
  				if (delta > 0) {
  					sp.scrollTop = scrolled = scrollTop + speed;
  				}
  			} else if (scrollTop > 0 && event.pageY - spOfs.top < sensitivity) {
  				sp.scrollTop = scrolled = scrollTop - speed;
  			}
  		} else {
  			scrollTop = $(document).scrollTop();
  			if (scrollTop > 0 && event.pageY - scrollTop < sensitivity) {
  				scrolled = scrollTop - speed;
  				$(document).scrollTop(scrolled);
  			} else if (
  				$(window).height() - (event.pageY - scrollTop) <
  				sensitivity
  			) {
  				scrolled = scrollTop + speed;
  				$(document).scrollTop(scrolled);
  			}
  		}
  		if (scrolled) {
  			tree.debug("autoScroll: " + scrolled + "px");
  		}
  		return scrolled;
  	}
docs: /* Implement auto scrolling when drag cursor is in top/bottom area of scroll parent.