Scope: standalone battery-powered electronic game devices — single-game handhelds, multi-game-library handhelds, tabletop reflex/memory games, and screen-based virtual pets; excludes swappable-cartridge/app-based video game consoles (Game.com, R-Zone, Switch-class hardware) and non-screen animatronic companions (Furby), which sit in other leaves.

Seed:
1. Equivalent of treadwear grade: built_in_game_count ("220-in-1") — compares well within one maker's line, loose across brands, since many libraries reuse one engine with palette/level swaps rather than distinct designs.
2. Sommelier notices first: these devices have a lineage (Game & Watch → Tiger LCD → 90s Tamagotchi/Giga Pet → 2020s My Arcade/Tamagotchi Uni) and today's revivals mostly repackage nostalgia IP on generic hardware rather than bespoke engineering — process matters more than the spec sheet.

Sources:
[wikipedia_handheld_electronic_game] https://en.wikipedia.org/wiki/Handheld_electronic_game — LED/LCD/VFD display eras, notable lines — fetched excerpt
[wikipedia_tiger_electronics] https://en.wikipedia.org/wiki/Tiger_Electronics — segmented vs dot-matrix LCD, licensing business model, wrist games — fetched excerpt (curl, scratch/tiger.html)
[wikipedia_game_and_watch] https://en.wikipedia.org/wiki/Game_%26_Watch — segmented LCD, Multi Screen dual-LCD — fetched excerpt (curl, scratch/gamewatch.html)
[wikipedia_tamagotchi] https://en.wikipedia.org/wiki/Tamagotchi — care meters, infrared linking, mono→color screens — fetched excerpt
[wikipedia_giga_pet] https://en.wikipedia.org/wiki/Giga_Pet — palm LCD unit, neglect/death mechanic — fetched excerpt
[wikipedia_simon] https://en.wikipedia.org/wiki/Simon_(game) — lengthening light/sound sequence, 4 buttons — fetched excerpt
[wikipedia_bop_it] https://en.wikipedia.org/wiki/Bop_It — voice commands, accelerating pace, AA/AAA, Vox Bop — fetched excerpt
[wikipedia_button_cell] https://en.wikipedia.org/wiki/Button_cell — ingestion hazard, 20mm+ highest risk — fetched excerpt
[wikipedia_toy_safety] https://en.wikipedia.org/wiki/Toy_safety — ASTM F963 scope, choking-hazard age warnings — fetched excerpt
[myarcade_gamestation_go] https://myarcadegaming.com/products/atari-gamestation-go — 200+ games, 7" color screen, rechargeable, HDMI/USB-C — curl fetch, scratch/gamestation-go.html
[myarcade_tetris_pixel_pocket] https://myarcadegaming.com/products/tetris-pixel-pocket — 1.8" color screen, 3 AAA, keychain, 10 bonus games — curl fetch, scratch/tetris-pixel.html

Branches:
game_format→single_game_handheld: Tiger's standalone handhelds use fixed-image segmented LCDs for one game each.
game_format→multi_game_handheld: My Arcade Gamestation Go stores 200+ games with HDMI/USB-C output.
game_format→tabletop_reflex_game: Simon/Bop It wire buttons/knobs/levers to an escalating-speed sequence, no screen.
game_format→virtual_pet: Tamagotchi/Giga Pet spend their screen on a simulated creature with needs, not a game to win.
player_count→group_pass_around: Bop It's Vox Bop mode passes the unit between players.
battery_system→replaceable_button_cell: button cells raise the swallow-hazard check (button_battery_lock) that AA/AAA and rechargeable units skip.

Noise (spec-sheet rows not promoted to facets):
- "Pop-out stand" (Gamestation Go) — accessory, not an expert-judged spec.
- Exact product dimensions (3.88 x 0.88 x 1") (Tetris Pixel Pocket) — covered qualitatively by form_factor instead.
- UPC/item numbers — not buyer-facing.
- Cartridge-based systems (Quiz Wiz, R-Zone, Game.com) — out of scope, closer to video-game hardware.
- Furby / animatronic companions — out of scope, no screen/game mechanic; sits with plush/figures.
- Hidden test/demo mode — not a buyer-facing attribute.

Corrections (2026-10-26):
- built_in_game_count.range.max lowered 300→200 to match the only cited source's "over 200" wording; no second source reaches 300.
- display_size_in.range.min raised 0.7→1.8in to match the smallest sourced figure (Tetris Pixel Pocket's 1.8" screen); 0.7 had no source.
- screen_type gained led_display/vfd_display values, sourced to wikipedia_handheld_electronic_game's own text on LED lights and VFD (incl. color) screens.
- Added input_mechanism (new value buttons_plus_paddle_or_trackball) to multi_game_handheld's then_ask, sourced to Gamestation Go's "paddle, trak-ball, d-pad, bumpers, numeric keypad" spec line.
- single_game_handheld: moved speed_progression from makes_irrelevant to then_ask — Game & Watch-style handhelds commonly escalate speed as their core mechanic.
- multi_game_handheld: added licensed_ip to then_ask for consistency with single_game_handheld (branded "-in-1" handhelds exist).
- age_grade definition: replaced unsourced "antenna caps" example with "clip-on key rings," sourced to Giga Pet's attached key ring (wikipedia_giga_pet, added to age_grade's evidence).
- wikipedia_button_cell reference's second supports line reworded from an overgeneralized single-incident claim to the page's own general statement ("Coin cells 20mm or larger cause the most serious injuries; children aged 5 and under are most at risk").