raw_to_item_error = [
  | `header_line_not_first of int
  | `header_line_without_version of (string * string) list
  | `header_line_wrong_sorting of string
  | `invalid_header_tag of int * string
  | `invalid_tag_value_list of int * string list
  | `reference_sequence_not_found of raw_alignment
  | parse_optional_error
  | parse_cigar_error
  | `wrong_flag of raw_alignment
  | `wrong_mapq of raw_alignment
  | `wrong_pnext of raw_alignment
  | `wrong_pos of raw_alignment
  | `wrong_qname of raw_alignment
  | `wrong_tlen of raw_alignment ]