A recent thread on the dita-users list discussed specialization as an extension of the DITA OT by restrictive substitution. This is best done by creating a DITA-OT plugin.

Plugins are overrides to the OT code that add functionality. Plugins are used to add new specializations to the OT and to define new specialization targets for output processing of the specialized elements. If they are designed properly, plugins can be added to an upgraded version of the OT and still run properly.

I decided to create a new Tutorials section on the DITA Users site for Plugins.

http://www.ditausers.org/tutorials/plug-ins/

It includes tutorials plus references to contributed plugins on SourceForge and the Yahoo! dita-users files area.

If you have any suggestions for more material on Plugins, please send it to me or leave a comment here.