function init() {
    if ( !atomicHelpers.setInitFlag( _dom ) ) {
      return standardType.UNDEFINED;
    }

    _isAccordion = _dom.classList.contains( BASE_CLASS + '__accordion' );

    var child;
    var len = _domChildren.length;

    for ( var i = 0; i < len; i++ ) {
      child = new Expandable( _domChildren[i] ).init();
      child.addEventListener( 'expandBegin', _childBeginExpand );
    }

    return this;
  }
/**
   * @returns {ExpandableGroup|undefined} An instance,
   *   or undefined if it was already initialized.
   */
@returns {ExpandableGroup|undefined} An instance,
or undefined if it was already initialized.
@returns { ExpandableGroup|undefined } An instance or undefined if it was already initialized .
function init() {
    if ( !atomicHelpers.setInitFlag( _dom ) ) {
      return standardType.UNDEFINED;
    }
    _isAccordion = _dom.classList.contains( BASE_CLASS + '__accordion' );
    var child;
    var len = _domChildren.length;
    for ( var i = 0; i < len; i++ ) {
      child = new Expandable( _domChildren[i] ).init();
      child.addEventListener( 'expandBegin', _childBeginExpand );
    }
    return this;
  }
function init ( ) { if ( ! atomicHelpers . setInitFlag ( _dom ) ) { return standardType . UNDEFINED ; } _isAccordion = _dom . classList . contains ( BASE_CLASS + '__accordion' ) ; var child ; var len = _domChildren . length ; for ( var i = 0 ; i < len ; i ++ ) { child = new Expandable ( _domChildren [ i ] ) . init ( ) ; child . addEventListener ( 'expandBegin' , _childBeginExpand ) ; } return this ; }
@returns {ExpandableGroup|undefined} An instance,
   or undefined if it was already initialized.
@returns { ExpandableGroup|undefined } An instance or undefined if it was already initialized .