Scope: Pet ID Tags & Charms = functional ID tags (stamped/deep-engraved/laser metal, QR/NFC smart, Apple AirTag holders, legally-issued license/rabies tags) worn on dog/cat/small-pet collars, plus decorative non-ID collar charms. Excludes implanted microchips and standalone GPS/cellular tracker collars (different product categories, not tags).

## Seed
1. pet-tags equivalent of weave/thread-count: engraving method and depth (stamped/deep-drag vs shallow laser) is the real durability lever, not the material brand name everyone leads with.
2. Allergist persona notices first: hidden nickel in base-metal/brass tags and plated charms worn against fur/skin for years — a dose-over-time contact-dermatitis risk novices don't check.

## Sources
- [wikipedia_pet_tag] https://en.wikipedia.org/wiki/Pet_tag — UK law requires an ID tag even with a microchip; materials/engraving; silencers — fetched: "dog owners are required by law to ensure that their dog is wearing an ID tag, even if the dog has already been microchipped"
- [wikipedia_dog_licence] https://en.wikipedia.org/wiki/Dog_licence — licensing/tag requirement varies by country/state/locality — fetched: "Dog licences are mandated by state and territory legislation but are issued by local governments"
- [wikipedia_microchip] https://en.wikipedia.org/wiki/Microchip_implant_(animal) — microchip is a surgical implant, not a wearable tag — fetched: "A microchip implant is an identifying integrated circuit placed under the skin of an animal"
- [wikipedia_nickel_allergy] https://en.wikipedia.org/wiki/Nickel_allergy — nickel as common contact allergen — fetched page title/lead confirms topic exists as sourced primer
- [boomerang_spec] https://www.boomerangtags.com/stainless-steel-tags-2/ — shapes/sizes in inches, deep-diamond-engrave vs laser claim, S-hook/split ring/rivet — fetched: "small: …….. 1″ diameter... medium: … 1 1/4″ diameter... large:……… 1 1/2″ diameter" and "a laser process just burns a light image into the top few microns"
- [tag4mypet_spec] https://tag4mypet.com/pages/pet-tags-size-guide — laser-engraved 0.78–1.25in, hand-stamped 1–1.25in, slide-on/AirTag-holder as separate catalog lines — fetched: "Minimum size: 0.78 inches Maximum size: 1 1/4 inches" (laser) and "Medium: 1 inch... Large: 1 1/4 inches" (stamped)
- [barkntag_guide] https://www.barkntag.com/blogs/ratgeber/dog-tag-material-comparison — material comparison table, 316L nickel-free claim, size-by-weight guidance — fetched: "High-quality stainless steel (316L Surgical Steel) is nickel-free" and "25 mm for small dogs... 35 mm" range in use-case table
- [lucysbarkery_guide] https://lucysbarkery.com/pet-id-tags-guide-2026/ — CPDT-KA trainer guide: QR/NFC pros/cons, silencer, double-sided engraving — fetched: "QR code and NFC tags store more data online... rely on the finder having a smartphone and internet access"

## Branches
- product_type=id_tag vs charm: different judging criteria stated explicitly by wikipedia_pet_tag (info on tag) vs boomerang/tag4mypet selling charms/AirTag-holders as separate lines from ID tags.
- pet_species=cat/dog: barkntag's "25mm for small dogs/under 3kg" vs "35mm large breed" sizing by weight supports species-driven size/attachment fork.
- primary_use_environment=frequent_water_exposure: barkntag's "Dog at the beach / lots of water → Stainless Steel (saltwater-resistant)" row supports material follow-up.
- info_format=qr_code_smart/nfc_smart makes engraving_method/text_capacity irrelevant: lucysbarkery states these "store more data online... without needing to replace the physical tag," i.e. no engraving to optimize.
- info_format=license_or_rabies_tag: wikipedia_dog_licence + wikipedia_pet_tag both describe this as a distinct, authority-issued object, not a retail engraving choice.
- primary_use_environment=rugged_outdoor_active→engraving_method, primary_use_environment=everyday_light_use→attachment_style, info_format=airtag_holder→attachment_style: editorial defaults, not cited to a source — rugged/outdoor use plausibly needs an engraving-depth follow-up before a durability recommendation, light everyday use defaults to the simplest attachment question, and an AirTag holder still has to physically attach to the collar so attachment_style is a reasonable next question even though info_format already made engraving/text facets irrelevant for it.

## Noise
- Price, appearance adjectives (shiny/matte/vintage) — cosmetic, redundant with material facet, not expertise.
- Durability/rust/engraving-quality star ratings (barkntag table) — folded into tag_material's why_experts_care rather than a separate facet.
- Care/cleaning instructions (polish brass, wipe with soap) — post-purchase maintenance, not a buying-time facet.
- Replacement-check-frequency advice ("check twice a year") — maintenance habit, not a product attribute.
- GPS/cellular tracker collars (Tractive, Fi, Whistle) — a different device category (powered, subscription, not a tag/charm); out of scope.
- Implanted microchip — surgical implant, not a tag; used only for mechanism contrast (wikipedia_microchip).

## Corrections (2026-10-26)
- Rewrote `text_capacity`'s why_experts_care/backfill_note and raised backfill_cost to high: re-fetched boomerang_spec shows bone=3 lines, round=6, heart=6 — the opposite ranking from the old heart/mini-vs-round/bone claim.
- Tightened `tag_size_diameter`'s range to {min:20,max:38}mm and rewrote its why_experts_care band breakdown to boomerang_spec's real 21/25/32/38mm tiers (corroborated by barkntag_guide's 25-35mm dog range); old 18/40mm range matched no cited source.
- Removed `pet_species=cat`'s `makes_irrelevant: [text_capacity]` — no sentence in the register or these notes ever tied cat ownership to text capacity becoming irrelevant.
- Added `chain_dangle` to `attachment_style`'s values: re-fetched boomerang_spec states pet-id buyers choose between a chain and a split ring/S-hook, a real option the facet was missing.
- Removed `product_type=charm`'s `makes_irrelevant: [legal_tag_requirement]` — a charm buyer can still separately need a legally required rabies/license tag, so dropping it on a charm purchase was unsupported.
- Added vocabulary entries for "Embossed" (engraving_method) and "Breakaway collar" (pet_species), both used elsewhere in the register without a definition.
- Documented three previously-uncited branch legs (rugged_outdoor_active→engraving_method, everyday_light_use→attachment_style, airtag_holder→attachment_style) as explicit editorial defaults in the Branches section above, rather than leaving them unexplained.
- Rejected the checker's Part D note on `charm_size_small_parts_risk`'s backfill_cost (medium vs low) and the Part F slide-on collar-width constraint — checker itself marked both "not required."