All user created messages must be trapped?

Richard Gaskin ambassador at
Thu Dec 8 17:03:07 EST 2005

Björnke von Gierke wrote:
> yes you got that right, from the docs:
> Unhandled messages:
> If a built-in message, a setProp trigger, or a getProp call passes 
> through the entire message path without finding a handler, it is ignored 
> by the engine (the last stop in the message path).
> If a message corresponding to a custom command or a custom function call 
> reaches the end of the message path without finding a handler, it causes 
> an execution error.

This behavior is in most cases what you want, since it indicates that 
what you were trying to do didn't work.

But if you do need to send messages which may or may not be handled, you 
can do that without error by making stub handlers in a backscript:

on MyMessage
end MyMessage

That was the message is technically handled, even though nothing happened.

For more info on backScripts see the Transcript Dictionary entry for the 
"insert" and "remove" commands.  Backscripts can be very handy.

  Richard Gaskin
  Managing Editor, revJournal
  Rev tips, tutorials and more:

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