static get properties() {
    return {
      /**
       * index number of the focused accordion
       */
      focusedIndex: { type: Number },
      /**
       * array of indices of the expanded accordions
       */
      expanded: { type: Array },
      /**
       * exclusive property allows only one accordion slot to be open at a time
       */
      exclusive: { type: Boolean },
    };
  }
# <lion-accordion> webcomponent

@customElement lion-accordion
@extends LitElement