iframes ARE part of XHTML and The Web ( -> w3.org ). JS isn't - but it's making that wall..
( ..in big part by empowering young, unexperienced or resume driven developers when making The Web painful to use - if I would like it, how you could call that relation other than.. SM ? )
iframes don't even come close to what you do with XHTML
Popovers are something completely different that only NOW come to HTML 5.