on event clause in state machine diagrams

[malmoth]

UML defines the following clause in states :
<event> / <action>. ie, in the state owning this clause, the action <action> is being executed when the event <event> occurs.
In EA, the clause is set with an operation tagged with the action 'on event'. The result in the diagramis is the operation
+ on event / <operation name>

But I cannot see where to declare the event name. When one read this clause, one just know that <operation name> must be executed on the occurence of a certain event, but one just don't know which event is this !!!

Have I made myself clear ?