If you are generating a placeholder serverside and replacing it clientside, there's no need to use a request parameter. You can just use the event context.
You only need a request parameter when appending to the URL in javascript rather than replacing a token. Note that if you have ValueEncoders registered for your types, you don't need to worry about String / Integer id's… you can use your domain objects / enums etc instead and let tapestry do the conversion for you.
