API Evangelist enhancements for the ATF eRegulations API

overlay: 1.0.0
info:
  title: API Evangelist enhancements for the ATF eRegulations API
  version: 1.0.0
extends: ../openapi/bureau-of-alcohol-tobacco-firearms-and-explosives-atf--eregulations-openapi.yml
x-generated: '2026-09-05'
x-method: generated
x-source: >-
  Records the runtime behaviour API Evangelist observed on 2026-09-05 that a
  consumer cannot learn from the endpoint shapes alone. Applied as an Overlay so
  the base description stays a plain statement of what the endpoints are.
actions:
  - target: $.info
    update:
      x-soft-404-warning: >-
        An unknown CFR part, version or notice id returns HTTP 200 with the
        eRegulations HTML site page, not 404. Clients MUST branch on Content-Type.
      x-rate-limits: >-
        None published; no X-RateLimit-*, RateLimit-* or Retry-After header is
        returned. Cache aggressively — regulation text changes at Federal Register
        cadence.
      x-status-page: none
      x-deprecation-policy: none
      x-sdks: none published
  - target: $.paths['/search'].get
    update:
      x-pagination:
        style: page-number
        param: page
        zero_based: true
        total_field: total_hits
        note: >-
          No next/prev link is returned and page size is undocumented; derive page
          count from total_hits and an observed page length.
      x-observed:
        q_firearm_total_hits: 1596
        q_firearm_scoped_478_2026_01141_total_hits: 50
  - target: $.paths['/regulation'].get
    update:
      x-observed-parts:
        - part: '447'
          versions: 10
          latest_effective: '2022-08-24'
        - part: '478'
          versions: 24
          latest_effective: '2026-01-22'
        - part: '479'
          versions: 8
          latest_effective: '2023-01-31'
        - part: '555'
          versions: 12
          latest_effective: '2019-12-26'
        - part: '646'
          versions: 2
          latest_effective: '2014-08-11'
        - part: '771'
          versions: 1
          latest_effective: '2019-12-26'
      x-freshness-warning: >-
        Coverage is uneven. 27 CFR 646 has not been reloaded since 2014; do not
        present it as current law without saying so.
  - target: $.paths['/diff/{part}/{older}/{newer}'].get
    update:
      x-empty-response-meaning: >-
        An empty object means no diff is stored for that pair, NOT that the two
        versions are identical. Observed on 478 between 2025-04872 and 2026-01141.
  - target: $.paths['/notice/{documentNumber}'].get
    update:
      x-join-key: >-
        documentNumber is the SAME string as the version id in
        /regulation/{part}/{version}. A text lookup and a rulemaking lookup join on
        it directly.