New Features Awaiting Implementation Interest

There are features that have been requested, but for which we are lacking implementor interest. Without two or more vendors interested in implementing the feature, they are unlikely to get added to the specs.

Feature	Interest indicated by...						Comments
	Mozilla (Firefox)	Opera	Microsoft (IE)	Apple (Safari)	Google (Chrome)	Others
Cross-origin seamless iframes	Boris Zbarsky				Adam Barth		Pending input on this thread
HTMLCanvasElement.printCallback API	Julian Viereck
Metadata API for media elements	Ralph Giles						Also needs a spec for the metadata schema
Adding defer/async to inline scripts	Jonas Sicking
<meta name="referrer">					Adam Barth
Location.ancestorOrigins					Already implemented		Negative feedback from Tobie Langel
A method to trigger autofill					Elliott Sprehn, Peter Kasting
Prerendering APIs					Gavin Peters		Needs detailed specification work to describe what happens with scripts running in the prerender context (since normally scripts can't run in non-active documents, and normally there's only one active document per session history).
APIs for 'palpable' content (at the bottom)					Ojan Vofai
Some way to add files to <input type=file>	Jonas Sicking				Nico Weber
Appcache: More detail in error events					Michael Nordman
Making drawImage() have a mode to clamp at source rectangle					Justin Novosad
Appcache: Interceptor Worker							Needs use cases as well
FormData
Canvas: Stroke alignment
Canvas: Page flipping for the 2D context					James Robinson
Canvas: control over when shadows paint
<img srcset>: a mechanism to enable adaptive images
locale=""
<video> currentTime and seek using rational numbers				Jer Noble			Would expose the video's timebase, too, assuming it's constant. See also next line.
video source material metrics (e.g. frame rate for fixed-frame-rate video data)
Exception object as fifth argument to onerror		zcorpan?
Cross-origin workers			Travis Leithead?		Ojan Vafai
Deferring <img> loads until the image is needed
API to request Web Worker latency guarantees (in exchange for guaranteeing low CPU usage)
SearchBox API					Tony Gentilcore

See also: Who to ask about stuff