code: func validateBlockSequence(bs []*Block) error {
  	if len(bs) <= 1 {
  		return nil
  	}
  
  	var metas []BlockMeta
  	for _, b := range bs {
  		metas = append(metas, b.meta)
  	}
  
  	overlaps := OverlappingBlocks(metas)
  	if len(overlaps) > 0 {
  		return errors.Errorf("block time ranges overlap: %s", overlaps)
  	}
  
  	return nil
  }
docs: // validateBlockSequence returns error if given block meta files indicate that some blocks overlaps within sequence.