Re: fallback color for background-image (ISSUE-5)

Brad Kemper wrote:
> 
> There might be other styles you would want to change if the image did 
> not load, besides just background-color. Maybe we need a ": 
> resources-not-loaded" pseudo-class that could be applied to any element, 
> class, etc., which would provide fallback properties when that element 
> contained external resources that did not load (for whatever reason).

I think that's getting a little too generic. Most of the time
if decorative images don't load it's not a big deal. For
backgrounds it's a readability issue, though.

The other important one that needs fallbacks is 'content', we're
handling that by making it take a comma-separated list of values.

   content: url(hello.png), "hello";

I guess you could argue that distinguishing between the cases where
this results in a replaced element (using hello.png) vs. where it's
just text ("hello") would be useful.

~fantasai