[whatwg] Simplified <picture> element draft

[Kornel Lesiński]

I've written down proposal for the simplified source selection algorithm:

http://geekhood.net/picture-element.html

This also includes variant of the idea from the recent "<picture> redux"  
proposal to use an actual <img> element as the basis for the <picture>  
element definition.

This draft doesn't include all features of src-N *yet*, but I expect this  
to be added either via extended srcset syntax to something like <source  
sizes> once there's consensus how to approach this.

To simplify implementation even further I've allowed UAs to flatten  
fallback DOM to a plaintext string (in case they need to emulate <img alt>  
for existing screen readers or accessibility APIs).

I've dropped usemap. It could be added, but I'm not sure if there is need  
for it.

I've specified very few IDL attributes. This area may need to be extended.

-- 
regards, Kornel