code: function _class_labeler(ce){
  	var ret = ce.class_label();
  	// Optional ID.
  	var cid = ce.class_id();
  	if( cid && cid !== ret ){
  	    ret = '[' + cid + '] ' + ret;
  	}
  	return ret;
      }
docs: Class label is main, but prepend class ID if available and different.