  Do not click on the page with the left mouse button!
  If you do, Down-arrow and Page-down will work OK.
  Autoscroll will still work unexpectedly though.
  Mouse-wheel roll works as expected regardless.

  Try Autoscroll / Page-down / Arrow-down

  Try Autoscroll / Page-down / Arrow-down

  Try Autoscroll / Page-down / Arrow-down

  Try Autoscroll / Page-down / Arrow-down

  Try Autoscroll / Page-down / Arrow-down

  Try Autoscroll / Page-down / Arrow-down

  Try Autoscroll / Page-down / Arrow-down

  Try Autoscroll / Page-down / Arrow-down

  Try Autoscroll / Page-down / Arrow-down

  Try Autoscroll / Page-down / Arrow-down

  Try Autoscroll / Page-down / Arrow-down

  Try Autoscroll / Page-down / Arrow-down

  Try Autoscroll / Page-down / Arrow-down

  Try Autoscroll / Page-down / Arrow-down

  Try Autoscroll / Page-down / Arrow-down

  Try Autoscroll / Page-down / Arrow-down

<html>
<body style="overflow: hidden; margin: 0px;">
<div style="overflow: auto; height: 100%;">
.. some black text to scroll ..
...
</div>

--> This red DIV (document structure display) should be clipped and BODY should be non-scrollable <--
</body>
</html>