Placeholders cannot also act as fallbacks inside of amp-img tags

What’s the issue?

amp-img tags with placeholders but no fallback remove the placeholder on failed load. The documentation seems to indicate that the placeholder should be used as a fallback if none exists. (Though I’m unsure if externally loaded images constitute “dynamic content” in this context.)

There appears to be no way to get this behavior without duplicating the nested elements.

How do we reproduce the issue?

See jsbin here. Note how the placeholder texts flash in while the image request is in flight. When the image request fails, the placeholder is removed. Fallback text is then visible only if that element is not also the placeholder.

If necessary, artificially slowing the network via debugging tools can make this more apparent.

What browsers are affected?

Latest Chrome (desktop and Android), Firefox (desktop), IE 11, and Edge

Which AMP version is affected?

1515614886756

[aghassemi]

What we should fix here: I think it makes sense for amp-img to follow the same model as amp-list and essentially do:

If the image fails to load:
  If there's a fallback element, display the fallback.
  Otherwise, continue displaying the placeholder.

This will be a change in behaviour, so we should be mindful of situations this may have negative effects. Possibly keep it under an experiment flag, slowing ramping it up to 100%.

/cc @ericlindley-g

[HarveyPeachey]

What was the status of this issue? I know it’s been 3 years so a very long time. Would be very useful if this feature was included to help solve https://github.com/bbc/simorgh/issues/8811.