I keep forgetting the various inconsistently named properties to move between document, window, and the owner frame of each. So here's how to do it in current browsers (IE10+, fwiw)...
// window -> frame
window.frameElement;
// document -> window
document.defaultView;
// frame -> window
frame.contentWindow;
// frame -> document
frame.contentDocument;
// window -> document (duh)
window.document;
// element -> document (the doc that created it, not necessarily the doc who has el in its DOM!)
el.ownerDocument;
Le sigh.