I have searched my way through the different DOM level specifications and I can't find any mention of a specified(!) method named like that. Unfortunately, it also doesn't seem to be specified anywhere else and to me it looks like it's a method that every implementation seems to have, but which is not part of the underlying specification that is implemented. Not entirely surprising, knowing how mixed up all the different implementations are, and yet interesting to see that every browser supports it.
In other words: It may be part of every DOM's implementation, but it is not part of the DOM.
Just because every implementation of an interface implements another method, doesn't make this method be part of the interface.
Last edited by Airblader; 10-10-2013 at 10:37 AM..