You're exactly right on how I named things; but using 'main_game:/controller#controller doesn't seem to be working for me.
I'm sending this message from my 'loader.script':
And in main_game:/controller#controller.script I have this debug line in 'function message(self, message_id, message, sender)':
...and nothing is being printed to the console. On the plus side, using the above URL isn't throwing an error, so I must be targeting SOMETHING that exists.
I know it's got to be some stupid noob mistake...
[btw, thanks for the tip about 'embedded game objects'.]