_calendarTemplate() {
    return html`
      <lion-calendar
        slot="content"
        .selectedDate="${
          /** @type {typeof LionInputDatepicker} */ (this.constructor).__getSyncDownValue(
            this.modelValue,
          )
        }"
        .minDate="${this.__calendarMinDate}"
        .maxDate="${this.__calendarMaxDate}"
        .disableDates="${ifDefined(this.__calendarDisableDates)}"
        @user-selected-date-changed="${this._onCalendarUserSelectedChanged}"
      ></lion-calendar>
    `;
  }
Subclassers can replace this with their custom extension of
LionCalendar, like `<my-calendar id="calendar"></my-calendar>`