get isInDST() {
    if (this.isOffsetFixed) {
      return false;
    } else {
      return (
        this.offset > this.set({ month: 1, day: 1 }).offset ||
        this.offset > this.set({ month: 5 }).offset
      );
    }
  }
Get whether the DateTime is in a DST.
@type {boolean}