User data is just a blob of string data that is associated with a Marker. It is loaded and saved with a Marker.
You can use it to store whatever string data you choose, there are no restrictions on size or content so long as it's a String type.
Examples
template.onSetUserData = function( menu, marker, programme ) { marker.userData = programme.name + " just a test of course."; app.getMarkerManager().broadcastMarkerChangeEvent(); }
String userData;