looks good for validator changes. ping me when you've submitted it.

Nice—excited to get this enhancement out!

Thanks! When should we see this in production?

After Jan 5th. Please see https://github.com/ampproject/amphtml/releases

Oh, so still slated for release...
As the documentation for this change is already updated here, I was trying... to no avail and getting error Response must be {items: []} object. Would appretiate is documentation includes a nested navigation example (or may be at https://www.ampbyexample.com).

(feature request is somewhat referenced here too: #3554 )

@jalajc This feature should be already on PROD (via #6745). Do you have an example you tried with? It should work, so if not - please send it to me and I'll debug.

@dvoytenko, Yups it was in prod the next day I wrote here. Nested list is perfect now.

I didn't update here as I was facing some issue with cliping of content (in terms of visibility on ui) which was not happening earlier and I was trying to figure out if my config/html layout is faulty.

One thing I notice is for nested list item, you still have to specify the src mandatorily and even src url is same that url endpoint is called as many times as you specify it.

To elaborate consider the following snippet for which mustache template is already defined as relatedLy

<amp-list width=300 height=75 layout=responsive template="relatedLy" src='https://suraurgeet_com/json/testrel.json' items="items1"></amp-list>
<amp-list width=300 height=75 layout=responsive template="relatedLy" src='https://suraurgeet_com/json/testrel.json' items="items2"></amp-list>
<amp-list width=300 height=75 layout=responsive template="relatedLy" src='https://suraurgeet_com/json/testrel.json' items="items3.items4"></amp-list>

Notice that

1. src attribute is same in all three and its response contains objects items1/2/3/4
2. items attribute is different in all three

Now whats happening is src, the CORS endpoint, is called three times!!

Can some configuration be done to avoid unnecessary repeated call to CORS end point.
Can src be not made optional, in that case use url specified in template and issue a warning in console in dev mode; but call that end point only once in a session as its not a live-list.

(Its like I am billed 3x for api that actually owe 1x 😃, plus more processing and latency )

@cramforce Would this be solved by the datasource idea that you had?

This will be handled by #7562.

Yes #7562 will do this.