To use general topics, the LispWorks application must define one or more subclasses of dde-topic. If an application supports only a single type of document, it will typically require only one topic class. If several different types of document are supported, it may be convenient to define a different topic class for each type of document.
If the application uses general topics, it should define a method on the dde-server-topics generic function, specializing on the application's server class.
LispWorks User Guide and Reference Manual - 21 Dec 2011