<my-custom-element itemscope>
    <button be-voke='
        Invoke someViewModel:someMethod.
    '>Click me</button>
    <span itemprop=greeting>Hello</span>
</my-custom-element>

What this does:

1. Because this enhancement is adorning the button element, assumes we would want to act on the click event. This can be overridden (see below).
2. Searches first for the closest element with an itemscope attribute. If not found, does a getRootNode().host. If that comes up empty, throws.
3. If name of element has a dash in the name, does an await whenDefined
4. Calls the method. Passes in the click event, and also the scope object, if applicable.