Which is true with regards to XPages Event Handlers? 

Event Handlers must be attached to an XPage control event. 

Event Handlers can be used to execute client-side and server-side JavaScript in the same event. 

When an Event Handler event is complete, client-side JavaScript can be inserted through the onCompleted property. 

It is not possible to use client-side JavaScript to specifically call server-side JavaScript code without using a partial refresh.