Allow multiple fallback URLs

[domenic]

@kmiller68 suggested we should allow multiple fallback URLs, and let the browser pick among them. For example, the browser could pick the one it already has in its cache.

I'm unsure whether the semantic would be picking one among them, and failing if that one doesn't work, or the browser picking an ordering among them, and trying each in turn if the first one fails.

[dtruffaut]

Plus the pipe trick looks really cheap.

Why not a srcset attribute ?

[domenic]

That seems like a separate issue; if you'd like to discuss syntax alternatives please open a new one.

(Quick answer: that doesn't work in import statements.)