Scope: Stationary pet containment at home — dog crates/indoor kennels, outdoor dog houses/kennels, bird cages, and small-animal cages (hamster/gerbil/guinea pig/rabbit). Excludes soft travel/airline carriers (leaf: pet-carriers), exercise pens (leaf: pet-playpens), aquariums/terrariums (separate leaves), cat trees/scratching furniture (leaf: pet-furniture-activity), and pet doors/barriers (separate leaf).

Seed:
1. Cages equivalent of thread-count-is-a-trap: listings lead with overall crate/cage size (inches, litres), but the real expert split is floor type and bar/wire spacing matching the specific pet's feet and head — size alone doesn't prevent injury.
2. A nurse would notice first: wire floors causing pressure injuries on small animals' feet (bumblefoot/ulcerative pododermatitis), the direct animal analog of a human pressure ulcer from unrelieved contact on a hard surface.

Sources:
[wiki_dog_crate] https://en.wikipedia.org/wiki/Dog_crate — crate material types (wire, plastic, aluminum, hybrid, soft-sided, decorative) and their trade-offs — fetched excerpt
[hsus_crate] https://www.humanesociety.org/resources/crate-training-101 — crate must let dog "stand up and turn around in" — fetched excerpt
[rspca_dog_env] https://www.rspca.org.uk/adviceandwelfare/pets/dogs/environment — crate/container must allow dog to "sit and stand up at full height, turn around easily and lie down in a natural position" — fetched excerpt
[wiki_doghouse] https://en.wikipedia.org/wiki/Doghouse — SPCA standard: outdoor shelter must be "structurally sound, weatherproof, insulated, of adequate size"; smart dog houses add temperature control — fetched excerpt
[wiki_birdcage] https://en.wikipedia.org/wiki/Birdcage — wrought iron/powder-coat vs stainless steel; wingspans (budgie ~30cm, cockatiel ~41cm, macaw 91–122cm); bars spaced so birds can't stick heads out; rectangular vs round; perch diameter — fetched excerpt
[rspca_bird] https://www.rspca.org.uk/adviceandwelfare/pets/birds/environment — aviary must be ≥4x largest bird's wingspan in each dimension; +20% per added bird; +5–10% per bird over two by weight class — fetched excerpt
[wiki_guineapig] https://en.wikipedia.org/wiki/Guinea_pig — wire mesh floors cause bumblefoot; solid-bottom cages preferred; C&C (cubes and coroplast) modular style — fetched excerpt
[wiki_hamstercage] https://en.wikipedia.org/wiki/Hamster_cage — min 100x50x50cm (Syrian)/100x50x40cm (dwarf), ~775 sq in floor; wire-top bar spacing ~12mm (Syrian) / ~8mm (dwarf), max ~1cm; wire floors cause bumblefoot; wire-top/plastic-tank/bin/aquarium styles — fetched excerpt
[pdsa_hamster] https://www.pdsa.org.uk/pet-help-and-advice/looking-after-your-pet/small-pets/hamsters-as-pets — min cage 100x50cm (cites German veterinary welfare association); bedding depth ≥25cm/10in — fetched excerpt
[rspca_rabbit_env] https://www.rspca.org.uk/adviceandwelfare/pets/rabbits/environment — min living space 3m x 2m x 1m for two rabbits; must stand on hind legs without ears touching roof; solid non-wire floor required — fetched excerpt

Branches:
- enclosure_type -> dog_crate branch: "A dog crate's defining spec is its frame material and size-to-fit" (wiki_dog_crate, hsus_crate, rspca_dog_env)
- enclosure_type -> outdoor_dog_house branch: governed by weatherproof/insulated/adequate-size standard (wiki_doghouse)
- enclosure_type -> bird_cage branch: governed by bar spacing and wingspan-scaled size (wiki_birdcage, rspca_bird)
- enclosure_type -> small_animal_cage branch: routes to small_animal_species, then floor type and minimum floor space dominate (wiki_guineapig, wiki_hamstercage, pdsa_hamster, rspca_rabbit_env)

Noise: price, brand, and star rating left out per rule. "Antique/decorative birdcage styling" (wiki_birdcage) left out — décor, not a functional facet. Exact IATA airline-crate certification left out — that governs travel carriers (leaf: pet-carriers), not stationary home cages.

Corrections (2026-10-26):
- wiki_hamstercage reference's first `supports` line corrected from "100x50x50cm Syrian / 100x50x40cm dwarf" to "110x50x50cm Syrian / 100x50x50cm dwarf" to match the source's actual text.
- `crate_size_fit.backfill_note` reworded: the inch-to-weight band mapping is now described as a sizing convention, not a number drawn from hsus_crate/rspca_dog_env, which support only the stand/turn/lie-down minimum.
- `house_size_fit.backfill_note` reworded the same way: the weight cutoffs are a convention, not a figure from wiki_doghouse, which supports only the qualitative "adequate size" standard.
- `crate_material.why_experts_care` softened "tested safer in vehicle crashes" to "may be safer in vehicle crashes" to match wiki_dog_crate's own hedge ("might also be safer in a car accident").
- `crate_material` now states in its `definition` and `why_experts_care` that wiki_dog_crate's "hybrid" (aluminum frame/coated-wire-mesh/plastic) type folds into the `heavy_duty_aluminum_steel` value, with the stated reason being shared durability; no new value added since no separate source distinguishes its fit/safety profile from that value.