I found that the HTMLOptionsCollection object inherits properties and methods from an HTMLCollection.
HTMLOptionsCollections->HTMLCollection->Object->null
Is there another type that also inherits HTMLCollection?
You will find other DOM interfaces that should inherit from the HTMLCollection in the HTML5 specification:
http://www.whatwg.org/specs/web-apps/current-work/multipage/common-dom-interfaces.html#collections-0
However, these objects are not necessarily implemented in modern browsers.