so I read the ampproject.org guide about iframe.
it says we should use amp-iframe.
I was wondering why https://www.ampproject.org/contact/ doesn't get validation error?
when I look at the source code of https://www.ampproject.org/contact/ , I see that it did not use to embed google forms.

I tried using just <iframe> to embed google map for the website I am making and I get a validation error.
However, I also do not get a validation error for embed <iframe> google forms.

is it because it is a google form?
thank you for your help!