2 ms·

It _is_ an HTML (and CSS) subset. JavaScript is used to implement custom elements, like amp-image. That's just how custom elements work.

• TazeTSchnitzel 11y ago
  It's not a subset, it's not a superset. It lacks some HTML things and adds new ones.
  • spankalee 11y ago
    Custom elements are a part of HTML, they can be part of a subset. Disqualifying custom elements from an HTML subset would be like claiming function declarations can't be in subsets of JavaScript.
    • TazeTSchnitzel 11y ago
      That's not really the same... HTML elements are more like keywords than functions.
      • spankalee 11y ago
        Not really. To continue the analogy, in HTML doesn't really have keywords, but has syntax in the form of brackets, quotes, =, etc. Tags are like function calls, and the built in tags are like the standard library. Until custom elements you couldn't declare "functions".