MDN URL: https://developer.mozilla.org/en-US/docs/Glossary/Site

What information was incorrect, unhelpful, or incomplete?

This page says that "scheme and port are not relevant" to sites.

Specific section or headline?

In the Examples section.

What did you expect to see?

Whether scheme is considered part of the definition of site is inconsistent across different specs. It's unfortunately incorrect to say it's not relevant.

According to the HTML standard, scheme is included: https://html.spec.whatwg.org/multipage/origin.html#sites
It literally says "A site is an opaque origin or a scheme-and-host".

This is a problem because the MDN page directly references the Cross-Origin Resource Policy, whose page references the HTML spec.

Did you test this? If so, how?

No.