"abstract" interface

[hfmanson]

Is it possible to create an interface which only can be extended and not instantiated like WebIDL's [NoInterfaceObject]?
e.g. at dom4 idl:

[NoInterfaceObject, Exposed=Window]
interface NonElementParentNode { Element? getElementById(DOMString elementId); };
Document implements NonElementParentNode;
DocumentFragment implements NonElementParentNode;

Here it would be nice that NonElementParentNode will not be suggested when declaring a variable

[danquirk]

See #6