Map format (XML):

<map> - root node, no additional attributes.
Regions and effects
Regions itself can't trigger effects. However, they can be used in a condition activating a door object, which has an <effect-on-open> node. To trigger an effect, you have to use this trick:
  <!-- xml describing door without image nor animations, to make sure it's invisible -->
  <objtype code="invisible-door" file="path/to/door-without-image.xml"> 
  
  <!-- door placed outside the map (x=-5, y=-5) -->
  <obj code="invisible-door" x="-5" y="-5">
    <cond check="is">
      <type>region-triggered</type>
      <param>REGIONNAME</param>
    </cond>
  </obj>
  
  <region name="REGIONNAME" x="10" y="10" scale="1" />
See conditions page for more info regarding the <cond> node.