As a first-time implementer of the DOM 4 specification, I was confused about the purpose of a transient registered observer. It is not clear at all from the text what it does, so it hampered my ability to implement the feature.

This archived w3c email thread helped out my understanding of the transient observer a lot when I read it:

http://lists.w3.org/Archives/Public/www-dom/2012JanMar/0069.html 

The text needs to have some sort of an explanation as to what a transient observer does. Something similar to the archived email I cited above.  I think it would help future implementers.