Custom elements are part of the HTML spec now, but the API and semantics are different to the early draft Chrome implemented. We should investigate deprecating and removing the old implementation.
I've created a negative test for this in https://github.com/w3c/web-platform-tests/pull/7580
At https://webengineshackfest.org/ I've also learned that YouTube sends code using document.registerElement if the UA identifies as Chrome.
Is there a roadmap doc for how Custom Elements v0 will get deprecated and removed? Is it blocked on removing Shadow DOM v0?
Comment 1 by dominicc@chromium.org
, Feb 15 2017