I think you should study the form of portal URL first (URL in 3.1.0 follows a quite simple pattern) to configure rewrite syntax (relevant tutorial exists on Apache)
Thank you for your answer!
My question was, and is, how to achieve any kind of rewrite, also tomcat is runnning standalone, so mod_rewrite isn't available.
Ofcourse I will figure out the specific rewrite rules out myself, if I can figure out how to get rewrite.properties to work.
I tried to configure a valve in server.xml. But I don't seem to know the right class name, which seems to differ from JBOSS (org.jboss.web.rewrite.RewriteValve).
If I have missed somewhere the description of this feature in the documentation, could you point me in the right direction?