Customized built-in elements aren't supported

• Component: DOM
• Status: RESOLVED DUPLICATE

[Andreas Deuschlinger]

The HTML Living Standard for Custom Elements specifies support to extend existing built-in elements, by:
- the `is="my-button"` attribute
  https://html.spec.whatwg.org/multipage/custom-elements.html#attr-is
- the `document.createElement('button', { is: 'my-button' })` second argument
  https://dom.spec.whatwg.org/#dom-elementcreationoptions-is

Example:
https://html.spec.whatwg.org/multipage/custom-elements.html#custom-elements-customized-builtin-example

The Webkit Status page gives incorrect information claiming that Custom Elements V1 are supported,
though in fact only "autonomous custom elements" are supported.
https://webkit.org/status/#feature-custom-elements

Caniuse informs about this incomplete implementation correctly:
https://caniuse.com/#feat=custom-elementsv1

Previous discussion about this on Github https://github.com/w3c/webcomponents/issues/509#issuecomment-222860736

[Ryosuke Niwa]

Our position has been that this feature shouldn't exist in the spec in the first place. I really don't understand how we ended up allowing Google to keep this feature in the HTML5 spec despite of our repeated objections.

*** This bug has been marked as a duplicate of bug 182671 ***

[Andreas Deuschlinger]

Thanks  a lot for your quick feedback:)

Meanwhile i came across element behaviors a the suggested has attributes:
https://www.npmjs.com/package/element-behaviors

Which is what I would really need:) But gies beyond this ticket...