Hence, all button event handlers (except keyPress, which also requires a key parameter) take the form:

on (eventName) {
  statements
}

A single button handler can respond to multiple events, separated by commas. For example:

on (rollover, rollOut) {
  // Invoke a custom function in response to both the rollOver and rollOut events
  playRandomSound( );
}

All movie clip event handlers take the form:

onClipEvent (eventName) {
  statements
}

Unlike button handlers, clip handlers can respond only to a single event.

10.4. Event Handlers		10.6. Creating Event Handlers