gistfile1.js

(function(){
	function focusInHandler(e){
		Event.findElement(e).fire("focus:in");
	}
	function focusOutHandler(e){
		Event.findElement(e).fire("focus:out");
	}

	if (document.addEventListener){
		document.addEventListener("focus", focusInHandler, true);
		document.addEventListener("blur", focusOutHandler, true);
	} else {
		document.observe("focusin", focusInHandler);
		document.observe("focusout", focusOutHandler);
	}
})();
document.on('focus:in', selector, function(){
	// on focus 
});
document.on('focus:out', selector, function(){
	// on blur
});

Deprecated? Maybe. Removed? Deprecated things like Element.ClassNames, Position, $continue, Insertion, Toggle are still not removed. Why such widely used (e.g. in scriptaculous, ajaxtags, livepipe, modalbox, tablekit) method like Event.element will be removed in the (near) future?

I don't know from the docs - http://api.prototypejs.org/dom/event/prototype/element/ and from I have communicated with the Prototype Core it will be removed some day. Prototype as a whole is moving really really slow :( But I prefer my code to use the no deprecated funcs. (as for ClassNames, Position, $continue, Insertation, Toggle I use a custom build and not include those)