IE DOMContentLoaded documentElement.doScroll

Question

Is there any reason why DOMContentLoaded trick for IE by Diego Perini is implemented only when window is not in iframe in popular JS Libraries?

jQuery:

//If IE and not a frame continually check to see if the document is ready

  var toplevel = false;

  try {
    toplevel = window.frameElement == null;
  } catch(e) {}

  if ( document.documentElement.doScroll && toplevel ) {
    doScrollCheck();
  }

Prototype:

document.observe('readystatechange', checkReadyState);
if (window == top)
  timer = pollDoScroll.defer();

Both of them checks is window is equal to top and if it is the document.documentElement.doScroll('left'); is used to check ready state. But why not to use it when window != top?

Answer 1

This bug report for YUI library states that doScroll in framed document doesn't work the same way as when run on top level (doesn't throw errors when document isn't ready).