[whatwg] ALT and equivalent representation

[Shannon]

What about this as a possible solution?

<img src="part1.png" altgroup="rating">
<img src="part2.png" altgroup="rating">
<img src="part3.png" altgroup="rating">
<altgroup id="rating" value="3/5">

I don't think this would raise any serious implementation issues as the 
logic is quite simple; If all elements in an altgroup are unavailable 
then display the value of the altgroup tag. The alt attribute would then 
be optional where altgroup is defined but required in all other cases.

Shannon