@type t() ::
  integer()
  | :EXTERNAL_REFERENCE_TYPE_OTHER
  | :EXTERNAL_REFERENCE_TYPE_VCS
  | :EXTERNAL_REFERENCE_TYPE_ISSUE_TRACKER
  | :EXTERNAL_REFERENCE_TYPE_WEBSITE
  | :EXTERNAL_REFERENCE_TYPE_ADVISORIES
  | :EXTERNAL_REFERENCE_TYPE_BOM
  | :EXTERNAL_REFERENCE_TYPE_MAILING_LIST
  | :EXTERNAL_REFERENCE_TYPE_SOCIAL
  | :EXTERNAL_REFERENCE_TYPE_CHAT
  | :EXTERNAL_REFERENCE_TYPE_DOCUMENTATION
  | :EXTERNAL_REFERENCE_TYPE_SUPPORT
  | :EXTERNAL_REFERENCE_TYPE_DISTRIBUTION
  | :EXTERNAL_REFERENCE_TYPE_LICENSE
  | :EXTERNAL_REFERENCE_TYPE_BUILD_META
  | :EXTERNAL_REFERENCE_TYPE_BUILD_SYSTEM
  | :EXTERNAL_REFERENCE_TYPE_SECURITY_CONTACT
  | :EXTERNAL_REFERENCE_TYPE_ATTESTATION
  | :EXTERNAL_REFERENCE_TYPE_THREAT_MODEL
  | :EXTERNAL_REFERENCE_TYPE_ADVERSARY_MODEL
  | :EXTERNAL_REFERENCE_TYPE_RISK_ASSESSMENT
  | :EXTERNAL_REFERENCE_TYPE_DISTRIBUTION_INTAKE
  | :EXTERNAL_REFERENCE_TYPE_VULNERABILITY_ASSERTION
  | :EXTERNAL_REFERENCE_TYPE_EXPLOITABILITY_STATEMENT
  | :EXTERNAL_REFERENCE_TYPE_PENTEST_REPORT
  | :EXTERNAL_REFERENCE_TYPE_STATIC_ANALYSIS_REPORT
  | :EXTERNAL_REFERENCE_TYPE_DYNAMIC_ANALYSIS_REPORT
  | :EXTERNAL_REFERENCE_TYPE_RUNTIME_ANALYSIS_REPORT
  | :EXTERNAL_REFERENCE_TYPE_COMPONENT_ANALYSIS_REPORT
  | :EXTERNAL_REFERENCE_TYPE_MATURITY_REPORT
  | :EXTERNAL_REFERENCE_TYPE_CERTIFICATION_REPORT
  | :EXTERNAL_REFERENCE_TYPE_QUALITY_METRICS
  | :EXTERNAL_REFERENCE_TYPE_CODIFIED_INFRASTRUCTURE
  | :EXTERNAL_REFERENCE_TYPE_MODEL_CARD
  | :EXTERNAL_REFERENCE_TYPE_POAM
  | :EXTERNAL_REFERENCE_TYPE_LOG
  | :EXTERNAL_REFERENCE_TYPE_CONFIGURATION
  | :EXTERNAL_REFERENCE_TYPE_EVIDENCE
  | :EXTERNAL_REFERENCE_TYPE_FORMULATION