Allow a site to express the need to be 100% AMP

[felixarntz]

Feature description

Related to #1235 and google/site-kit-wp#2998, it looks like currently it is impossible for a third-party to really know whether the AMP plugin is truly using AMP-only, since even in Standard Mode there are ways to opt out e.g. on a per-post basis. While this makes sense to most end users of the AMP plugin, for users (arguably with enough technical knowledge) that want to be a 100% AMP-only, this results in sub-optimal UX, for example in Site Kit:

• For our Tag Manager module, we have to prompt users to set up a "web" and "amp" container separately, based on their AMP configuration.
• Per Ensure a Web container is available for selection during Tag Manager module setup if using Standard mode AMP - when not all URLs are AMP google/site-kit-wp#2998, we now always require them to set up both as soon as the AMP plugin is active - which is unnecessary complexity if a user wants their site to be 100% AMP at all cost.
• A user that wants their site to be 100% AMP with no exceptions should not be required to set up a non-AMP version of the Tag Manager container, since it's useless for them.

To avoid the need for the above, it should be possible to indicate somehow that the site should be 100% AMP, so that other plugins can act accordingly with their integrations - essentially some sort of "strict" Standard Mode. I see this might be more of an edge-case, so maybe this could even be a configuration only controllable via filter.

In such a strict mode, I would envision no opt-out UI being displayed anywhere, and any non-AMP compatible URLs continuing with validation errors until the user resolves them.

cc @westonruter

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[westonruter]

See also prior discussion in google/site-kit-wp#2998 (comment):

@westonruter Given the above, it would be great to somehow indicate to the AMP plugin that you really only want AMP, everywhere. Almost like "strict mode". That may be a good enhancement, potentially just as a simple filter initially which would prevent any opt-outs, as it would give certain guarantees which would result in better UX for cases like ours here.

Yeah, it's something we've thought about. We had an issue for it: #2314. But we decided against it. The reality is that the majority of sites need the ability for AMP to be turned off in certain cases. Given that the AMP-compatible ecosystem of themes and plugins are not complete, the number of sites that run in Standard mode is still small in relation to sites in a paired mode (Reader/Transitional). And then among the Standard mode sites, there is a need to often turn off AMP for individual posts/pages (e.g. shopping cart), or to only have AMP enabled for certain templates (singular). So even if we added the ability for a site to only ever serve AMP pages no matter what without any ability to turn it off, the number would likely be very small who would access this streamlined analytics screen in Site Kit. It's not a scenario that is yet common enough to worry about, IMO.

See also #1864 and #2724 (comment).

We'll likely be revisiting this with Bento because a site would be able to serve all pages using AMP/Bento components without the need to disable AMP selectively for certain templates. When the least-restrictive sandboxing enforcement enabled (L1, #5549 (comment)) custom scripts would not be sanitized from AMP pages. So if you have custom JS on your shopping cart page, it could remain and live alongside Bento components on the same page (e.g. amp-analytics).

L2 sandboxing means only Bento components are allowed, and L3 sandboxing means only “AMP-certified” components are allowed.

So instead of there being a option to opt-out of AMP for a template, it's likely that what this instead could look like is to opt-out of L3 enforcement. This would likely be a power user feature and may not even be relevant to show in the UI.

The intention is that if a user has selected L1 sandboxing, but a page has no markup that would make it violate L3 sandboxing, that we'd automatically upgrade that page to be marked as a valid AMP page. The L1 sandboxing thus would break no pages out of the box. If you want to be more strict, then you'd select L2 or L3 for your site. Only in this latter more-technical case, would you potentially need to opt-out of sanitization on a per-post basis.

In any case, if amp-analytics were made available as a Bento component, then it could be used exclusively in Site Kit because it would work on AMP and non-AMP pages alike. But I don't believe amp-analytics is going to be made available to Bento soon.