Selectors

I tried to write a unit test that puts ten Integer objects (0 - 9) into a space, and then create a second space with the same destination, but with a filter to only get values > 5, but after doing some reading, it looks like the selector's in JMS are based on the Message headers, not the body.  So ActiveSpace probably needs a way to set headers (or call them attributes) on an object. Or I could be missing something that is already there?