The element element defines a custom element. Note: This element has been deprecated, and is not supported by any browser. See document.register for the standard custom element definition.
Custom elements are new types of DOM elements that can be defined by authors.
Custom elements can define presentation aspects like decorators. Unlike a decorator, which can be applied or unapplied to a given element, the element’s type is fixed. So custom elements can also define new state and behavior, which decorators can’t do because of their ephemeral nature.