Note that at some point we will not need to capture the required_parent_name in the error. We could instead capture the spec_name alone. Then the spec_name could be looked up to obtain the required_parent_name (or other properties depending on the error). This will be made possible by #3817. However, that is not yet available, so what you are doing here is the perfect approach in the time being.

Yep I initially was retrieving it by looking up the tag spec in AMP_Allowed_Tags_Generated::class, but I realized it was available in the sanitizer so I took it from there.

This will be made possible by #3817.

Awesome, made a note of that.

Not sure what to do here if the scheme could not be parsed, defaulting to an empty string for now.

Maybe null would be more appropriate?

Oh I see, it's used in a string. Yeah, an empty string seems fine for now.

Actually, since code is now being used as opposed to quotes, then I think something else is needed:

I've went ahead and removed the DISALLOWED_TAG_MULTIPLE_CHOICES error code as I don't see a meaningful way of displaying the multiple validation errors on the page. Instead, each error will be sanitized separately which allows for each to be viewed.

I'm removing any other keys that could potentially make the validation error unique (but it should not). Take for example this HTML element:

<stop offset="5%" stop-color="gold" />

This would raise two separate MANDATORY_TAG_ANCESTOR validation errors, but each would have its own required_ancestor_name (lineargradient and radialgradient), making each validation error unique.

Actually, since code is now being used as opposed to quotes, then I think something else is needed:

Given a Custom HTML block with the following markup:

<amp-accordion id="my-accordion" disable-session-states="">
  <section>
    <h2>Section 1</h2>
    <p>Content in section 12.</p>
  </section>
  <section>
    <h2>Section 2</h2>
    <div>Content in section 2.</div>
  </section>
  <section expanded="">
    <!--<h2>Section 3</h2>-->
    <amp-img src="/static/inline-examples/images/squirrel.jpg" width="320" height="256"></amp-img>
  </section>
</amp-accordion>

This is invalid because of the h2 being commented out. The amp-accordion component requires an h2 followed by a div or a p. The validation errors for this are not expected, however:

Notice the amp-img lacks the expected Custom HTML source.

I've fixed this here in feababc by breaking the loop of validation error reporting once a markup causing validation error is removed.

This will probably make this code no longer necessary:

Though it doesn't hurt to have it in there.

Notice the amp-img lacks the expected Custom HTML source.

Good catch!

This will probably make this code no longer necessary:

In this context yes, but it could potentially prevent an error being thrown when attempting to remove a node multiple times.