Custom element extended built-in support and special `is` attribute

document.createElement support additional options, namely is for custom elements that are extended. You can see that no additional arguments are sent to document.createElement.

Since custom elements are a goto solution for when limitations of Elm are crossed, allowing more support for them would be worthwhile. I tried in vain both using Html.Attributes.property and Html.Attributes.attribute because it must be set on element creation .

I would suggest similar to _VirtualDom_nodeNS, to have _VirtualDom_nodeIs or _VirtualDom_extendedNode that takes a string is like the namespace variable that applies it to document.createElement(tag, { is: is }). It could then be exposed in Html as a special case for Html.Attributes.is or Html.extendedNode.

This is related to Html issue https://github.com/elm/html/issues/192

[rlefevre]

@enjoythelive1 According to https://discourse.elm-lang.org/t/calling-dom-methods-from-elm/5701/15 and https://caniuse.com/#search=custom elements, it’s not possible to customize built-in elements with the is syntax in Safari. If confirmed, this would lower significantly the interest of adding support for it.

[boccato]

On the discussion about the Safari issue it is recomended to use a polyfill (https://github.com/ungap/custom-elements) which not only makes it work on Safari but also on older versions of other browsers.

https://bugs.webkit.org/show_bug.cgi?id=182671