Affinity Google AMP Guide 1
AMP HTML is HTML with some restrictions for reliable performance and some extensions for building rich content beyond basic HTML.
Though most tags in an AMP HTML page are regular HTML tags, some HTML tags are replaced with AMP-specific tags.Affinity Google AMP Guide 2
The AMP JS library ensures the fast rendering of AMP HTML pages. The Google AMP Cache (optionally) delivers the AMP HTML pages.
AMP HTML is basically HTML extended with custom AMP properties.
Among the biggest optimizations is the fact that it makes everything that comes from external resources asynchronous, so nothing in the page can block anything from rendering.
References:
ampproject.org
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