+------------------+
|                  |
|      Div         |
+------------------+
|         |        |
| section | section|
+---------|--------+

function onScroll(e){
    if(scollMarginToTop > marginTop_of_box1){
      e.preventDefault();
      if(marginTop_of_box1 < height_of_box1)
        marginTop_of_box1 - scrolledPixels (only if scrolled down otherwise + scrolledPixels)
      else
        start scrolling of box 2
    }
  }