function docjslib_moveVertically(id, increment) {
  if (NS4) eval(id).top += increment
  else eval(id).style.pixelTop += increment;
}

Let's see a typical example. The moveUp() function moves up two pages, firstPage and secondPage, and then switches between the pages when the top value of lowerPage becomes negative:

function moveUp() {
    docjslib_moveVertically(firstPage, -Gincrement);
    docjslib_moveVertically(secondPage, -Gincrement);
    if (docjslib_getElementTop(lowerPage) <= 0) { 
       docjslib_moveVertically(upperPage, docjslib_getElementHeight(upperPage) * 2);
       rotateThePages();
     }
}

Notice that there is not a single check for the browser identification. All browser-dependent stuff is handled by DOCJSLIB. To learn more about DOCJSLIB library and its usage in implementing a scroller, read Column33, DOCJSLIB Version 4.0: Scrollers, Watermarks, and Games.

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