Element Failure Mode

	Hello, everyone - first time poster here, so please be gentle.  :)
I did talk to one guy on the IE team who suggested I post this here as it
may make more sense as a change to HTTP, so here goes:

	One thing that has recently become a really big deal for UI
integrity is the failure of external resources to load.  One of the primary
reasons people use external resources is to limit the amount of development
they have to do and/or to reduce their bandwidth needs.  However, when an
external resource fails there is no practical way for them to be alerted to
that fact without creating some pretty hacky JS that is usually resource
specific.  As there could be half a dozen or more external resources on a
modern widget-heavy webpage, that's a lot of dev work today that's not very
portable.  Given that a huge percentage of sites are using external
resources, I keep thinking it would be really helpful to have a fallback
mechanism when external resources fail to load.  Here are some examples of
what I was thinking:

	<link rel="stylesheet" type="text/css"
href="http://remote.host/css.css" alternate="/css/css.css"
alert="/alert.aspx?error=css_load_failure" >
	<script type="text/javascript" src="http://remote.host/js.js"
alternate="/js/js.js" alert="/alert.aspx?error=js_load_failure"></script>
	<img src="http://remote.host/image/img.jpg" alternate="/img/img.jpg"
alert="/alert.aspx?error=image_load_failure">
	...

	The "alternate" tag (or whatever you want to call it) defines the
local resource that should be loaded if the remote resource fails to load.
That way at least there is some fallback mechanism that is browser agnostic,
and doesn't rely on additional hacky JavaScript.  I also had the idea that
it should allow for an alert mechanism to alert webmasters that third party
content failed to load which could have all kinds of adverse effects on the
page load time, UI integrity and even site functionality, so they can take
action.  Maybe another option would to be to provide a parameter for sending
an alert when it takes more than a certain amount of time to load - so
webmasters know when the 3rd party is responding too slowly?  For some
reference please read the recent article
http://www.troyhunt.com/2012/03/browsing-broken-web-software-developer.html
where sites have all sorts of bizarre failure modes when external resources
are unavailable.  Just because a webserver can reach the 3rd party doesn't
mean the client can, so this could be a nice way to provide a sane and
ubiquitous failure mode to web developers.

	Yes, this could leak some information across domains, but that is
already possible due to onerror event handlers, detecting certain attributes
in CSS and variables in JavaScript, so I don't think this adds much
additional in the way of security problems, but it's worth thinking about
anyway.  I would appreciate any thoughtful responses.  Thank you!

Robert Hansen, CISSP
CEO, Falling Rock Networks
Cell: (530) 521-2542
FAX: (512) 628-6299