Peter Gruenbaum has written a great article in the November 2010 issue of MSDN Magazine about the why and how of documenting APIs . You can read it online here: Hello World! A Coder's Guide to Writing API Documentation .

A new WPF 3.5 feature in the Annotations area is the capability to match annotations with the corresponding annotated objects. For example, you can now implement a document viewing application that has a comments pane, where the paragraph that contains the corresponding comment (a text sticky note in...