XML Events Question

Hi all!
 
I searched the web and didnt find any answer..could anybody pls. explain
the difference between
EventListener and EventHandler in context of XML Events.
 
XForms Example:
 
<trigger>
  <label>Click me</label>
  <action ev:event="xforms-activate">
    <reset model="thismodel"/>
    <setvalue ref="."/>
  </action>
</trigger>
 
Element action is the EventListener for Events occurring on target
Element trigger but it also the default handler for this event. Is there
a difference between listener and handler?? And what is the relation
between element action  (EventListener and EventHandler for target
trigger) and the concret subactions (reset,setvalue) in terms of the XML
Events spec.?? 
 
Many thanks
 
mc