h `rel=amphtml` pointing to
its matching AMP document in the same language.
* Every AMP document must have a link tag with `rel=canonical` pointing to
its matching canonical desktop document, again, in the same language.
* Every canonical document must have a link tag with `rel=alternate` and an
`hreflang` attribute for each alternative language version of the canonical document.
* Every AMP document must have a link tag with `rel=alternate` and an
`hreflang` attribute for each alternative language version 