code: function toggleTargetState( element ) {
    if ( element.classList.contains( this.classes.targetExpanded ) ) {
      this.ui.target.classList.add( this.classes.targetCollapsed );
      this.ui.target.classList.remove( this.classes.targetExpanded );
    } else {
      this.ui.target.classList.add( this.classes.targetExpanded );
      this.ui.target.classList.remove( this.classes.targetCollapsed );
    }
  }
docs: Toggle an expandable to open or closed.
  @param {HTMLNode} element - The expandable target HTML DOM element.