Rule explainer

Français · Type: reference · Audience: author · Context: local Studio · Status: ready · Applies from: 4.2.1

The local Studio · contract: stable · verified by CI (support matrix of 4.4.0, 2026-10-23): Chromium end to end (the Studio's checks); Windows: the unit suite only · automated checks: jobs e2e, windows; CI plan e2e, windows; 2 test files · people's passes: studio-hero-matrix not run (#238) · known limits: explainer-live-state-only

The Play tab's Why? panel answers "what happens if the player does this, now?": pick a verb, an item and a target, and it lists every rule that could answer, each condition evaluated against the live state of the game in the frame, and which answer wins.

Where it is

In the Studio's Play tab, under the game's live state (Play and replay a session). Its heading reads "Why? — the rules that could answer, first ✓ wins". It reads the game running in the frame, so it follows what you play. Local Studio only: on a hosted Studio the game is on another origin and the panel is left out.

Inputs

Field	Values	Default
Verb	The game's verbs	The first verb
Item	An item in the bag now, or `(no item)`	`(no item)`
Target	What the action is on: a target of the current room, or an item in the bag (`bag: <id>`)	`(target)`: the panel says "Pick a target."

With an item, the action is "verb item → target" (use key on door); without one, "verb target".

Which rules are listed

The room's rules (on of the current room) first, then the game's rules (rules.on of the game), in their written order. A rule is listed when its verb includes the verb picked and its targets match: a is the target (or the item when there is one) and b the target when there is an item. For two items, the rule also matches the other way round (item and target swapped).

What each line shows

The mark: ▶ the rule that wins (the first whose condition holds), ✓ a rule whose condition holds but comes after the winner, ✗ a rule whose condition does not hold.
The rule's id, or <room>.on[<n>] / game.on[<n>] when it has none, and "(exit)" for an exit rule.
The verb and targets it answers, then its condition, each part evaluated ✓ / ✗ against the live state, nested as the condition is.

When no rule answers

The panel says which answer the engine falls back to: "No rule answers: …"

Action	Fallback named
look at a target, which has a look line (in the room or on the item)	the look line
look at a target without one	the look fallback
talk to a target with conversation topics in the room	the conversation topics
talk to the game's hint item	the hints
talk otherwise	the talk fallback
anything else	a kind reaction, a refusal or the fallback line

Limit · explainer-live-state-only The panel judges the state in the frame now: it does not search for a state where a rule would hold (that is the solver's job, Check), and it does not run the rule. Rules a script or a listener answers outside a verb are not listed.

Reactions, Conditions.
src/studio/play.ts (the panel, explainCond).