code: public String getObjectProperty(int groupID, int objectID,
  			String propertyName, String def) {
  		if (groupID >= 0 && groupID < objectGroups.size()) {
  			ObjectGroup grp = (ObjectGroup) objectGroups.get(groupID);
  			if (objectID >= 0 && objectID < grp.objects.size()) {
  				GroupObject object = (GroupObject) grp.objects.get(objectID);
  
  				if (object == null) {
  					return def;
  				}
  				if (object.props == null) {
  					return def;
  				}
  
  				return object.props.getProperty(propertyName, def);
  			}
  		}
  		return def;
  	}
docs: Looks for a property with the given name and returns it's value. If no
  property is found, def is returned.
  
  @param groupID
  Index of a group
  @param objectID
  Index of an object
  @param propertyName
  Name of a property
  @param def
  default value to return, if no property is found
  @return The value of the property with the given name or def, if there is
  no property with that name.