I have purchased the book Tomcat: The Definitive Guide. (Tomcat 6.0 2nd Edition)
I believe it is missing mention of a useful Tomcat configuration setting:
It does not mention the use of the crossContext="true/false" switch which can be used in the Tomcat server.xml file Host Context, to allow cross-context use of resources. For instance, crossContext must be set to "true" if you need to specify an external context in the c:import JSTL tag used in JSP pages.