missing classes in

org.scalajs.dom.raw:

• ShadowRoot
• HTMLSlotElement
• HTMLTemplateElement

in Element:

/** Creates a shadow root for element and returns it. */
def attachShadow(init:js.Any):ShadowRoot

• CustomElementRegistry

in Window:

def customElements:CustomElementRegistry

new interface that HTMLElement should extends

interface Slotable {
    readonly assignedSlot: HTMLSlotElement | null;
}

caniuse of ShadowDom

Should I send PR or we are not interested this API until it is covered by all browsers?