@type t() ::
  integer()
  | :EVIDENCE_FIELD_NULL
  | :EVIDENCE_FIELD_GROUP
  | :EVIDENCE_FIELD_NAME
  | :EVIDENCE_FIELD_VERSION
  | :EVIDENCE_FIELD_PURL
  | :EVIDENCE_FIELD_CPE
  | :EVIDENCE_FIELD_SWID
  | :EVIDENCE_FIELD_HASH