Scope: Diving, Snorkeling & Swim = masks, snorkels, fins, dive computers, and swim goggles. Excludes wetsuits/drysuits (own leaf "wetsuits"), life jackets/PFDs (own leaf "flotation"), pool floats/toys ("pool-accessories"), and watercraft ("watercrafts").

Seed:
1. Diving equivalent of treadwear grade: a mask/snorkel's certification to EN 16805 / EN 1972 (tempered glass, dead-space volume) — a spec that only means something once you know the standard behind it, like UTQG only compares within a brand.
2. Allergist persona would notice first: snorkel dead-space volume (re-breathed CO2) and silicone vs rubber/PVC skirt material for skin contact — exposure/dose framing most buyers never consider.

Sources:
- [wikipedia_diving_mask] https://en.wikipedia.org/wiki/Diving_mask — lens config, skirt material, internal volume, EN 16805/ANSI Z87.11, tempered glass — fetched and grepped verbatim.
- [wikipedia_snorkel] https://en.wikipedia.org/wiki/Snorkel_(swimming) — EN 1972 length/volume classes, valve types, mounting, BS 8647 — fetched and grepped verbatim.
- [wikipedia_swim_fin] https://en.wikipedia.org/wiki/Swim_fin — foot pocket types, blade material, split-fin study, stiffness/leg-power study — fetched and grepped verbatim.
- [wikipedia_dive_computer] https://en.wikipedia.org/wiki/Dive_computer — Bühlmann/RGBM/VPM algorithm families, wireless tank-pressure transmitter — fetched and grepped verbatim; confirmed no EN13319 mention, so no standard claimed for computers.
- [en_standard_en1972] en-standard.eu BS EN 1972:2015 product page — standard title and scope (snorkel safety requirements) — fetched and grepped verbatim.
- [en_standard_en16805] en-standard.eu BS EN 16805:2015 product page — standard title and scope (diving mask eye protection, excludes full-face) — fetched and grepped verbatim.
- [suunto_dive_computers] suunto.com dive computer product listing — "view tank pressure on your dive computer" air-integration language — fetched and grepped verbatim.
- [speedo_goggles] speedo.com goggles catalog — shop-by-lens (coloured/anti-fog/polarised/mirrored) and shop-by-type (training/racing/recreation) nav categories — fetched and grepped verbatim.

Branches: Split 1 "activity" (scuba/snorkel/pool) makes irrelevant the gear facets the other activities don't touch (e.g. pool swimming drops all snorkel and dive-computer facets). Split 2 "gear_type" (mask/snorkel/fins/dive_computer/goggles) routes to each type's own facet set per the coverage test's "bundle" rule.

Noise (spec rows seen but not made facets):
- Mask strap/buckle style (quick-release vs plain) — minor, not a buying decision driver in sources.
- Dive computer screen color vs monochrome — cosmetic, not covered by any sourced comparison.
- Goggle strap material (silicone vs latex) — not distinct enough from skirt-material logic already covered for masks; no dedicated source.
- Price, brand, star rating — never facets per rule.
- Full regulator/BCD specs — out of scope; no separate facet set built since the leaf label names mask/snorkel/swim gear, not scuba life-support hardware, and no catalog sibling covers it either; flagged as a gap rather than guessed.

WebSearch was exhausted for this session; all research used WebFetch (orientation) cross-checked with direct curl+grep of the same URLs in scratch/diving/, plus en-standard.eu and brand pages reached via curl.

Corrections (2026-10-26):
- mask_certification.listing_field_hint said to search for "ANSI Z87.1"; fixed to "ANSI Z87.11" to match the diving-specific standard the facet actually cites.
- dc_algorithm_family.backfill_note now folds the Thalmann VVAL18 family (named in wikipedia_dive_computer alongside Bühlmann/RGBM/VPM) into proprietary_blend so it isn't left uncoded.
- snorkel_mount_style.source changed from listing to derived; its own listing_field_hint described image-based inference, not a stated listing text field.
- snorkel_certification's BS 8647 claim now has a second citation, en_standard_bs8647 (en-standard.eu BS 8647:2024 product page, fetched to scratch/fix-diving/bs8647_product.html), matching the two-source pattern used for EN 16805 and EN 1972.
- vocabulary gained "RGBM" and "VPM" entries; both appear in dc_algorithm_family's values and were previously undefined, though already supported by wikipedia_dive_computer.
- Added a regulator facet set (regulator_first_stage_balance, regulator_connection_type, regulator_cold_water_rated, regulator_octopus_included; evidence wikipedia_diving_regulator, fetched to scratch/check-diving/wiki_regulator_text.txt) and a BCD facet set (bcd_style, bcd_weight_integration, bcd_lift_capacity_class; evidence scubadiverlife_bcd, scratch/check-diving/sdl_bcd_text.txt), gated behind two new gear_type values ("regulator", "bcd"), closing the life-support-gear coverage gap the checker flagged. No numeric lift-capacity figures were found in the fetched source, so bcd_lift_capacity_class stays qualitative (standard_recreational vs. higher_lift_technical) rather than inventing a lbs/kg range.