handleBlur (event) {
      if (
        this._isOpen &&
        this.closeOnBlur &&
        this.contentNode &&
        this.triggerNode &&
        !this.contentNode.contains(event.relatedTarget) &&
        !this.triggerNode.contains(event.relatedTarget)
      ) {
        this.closePopover()
      }
    }
Handles blur event
@param {Event} e `blur` event object