Code
aspectxml
An Aspect-Oriented XML Weaving Engine (AXLE)
To learn more about the engine and the intricacies of its usage, please see the following overview and tutorials published to XML.com in August and September of 2005.
Original Idea
http://www.oreillynet.com/xml/blog/2005/08/assets_atom_feeds_and_aspectxm.html
Code Overview :: High Level
http://www.oreillynet.com/xml/blog/2005/09/part_3_assets_atom_feeds_and_a.html
Code Overview :: Low Level
http://www.oreillynet.com/xml/blog/2005/08/part_2_assets_atom_feeds_and_a.html