Passing Parameters to Event Handlers

I've tried passing parameters to my event handlers using the same method
that is used for check commands:  command!arg1!arg2.  However, I receive an
error stating that the handler command!arg1!arg2 does not exist when I check
the configuration using the -v switch.

I then tried using command;arg1, which did not produce any errors, but that
parameter is not being passed.

What am I missing?

TIA

Mike