It can be very useful to run a Rhino shell to learn the subtleties of the Rhino javascript syntax used by Flow.
This is explained here, but basically you can start the shell with
java -cp path-to-rhino-jar org.mozilla.javascript.tools.shell.Main |
Using Cocoon's version of rhino this becomes
java -cp lib/core/rhino1.5r4-continuations-20040228.jar org.mozilla.javascript.tools.shell.Main |