Shadow DOM and Fallback contents for images

Hi, 

  I am interested in using UserAgent shadow DOM to represent alternate text
for images (fallback content) on Blink. I am posting it here as the dev list
on blink felt this was more a specification issue. Here is a sample code
that closely describes the use case:  Jsfiddle.net/sQWHz/3/ 

We can see couple of issues with User interaction

1. Selections - Which the specification is clear. It will not allow the
selection range cannot span across different node trees. This again would
hinder seamless experience with selection.

2. Editing - The spec says that the contenteditable attribute should not be
propagated from the shadow host to the shadow root. Does this mean that and
Shadow DOM cannot participate in editing? This I find is limiting to use
shadow DOM to represent fallback content   

3. Accessibility - Since we will be changing the final composition of the
DOM, should accessibility be affected by it?

     for ex

                       <img alt="car" title="car.png"/> 

                                             The final composition would
look like

                                             <img ...>

                                                <Text>car 

                                                

Would like to hear about your opinions on this.

 

Regards

Sudarshan