Glossary

The vocabulary of the Screenplay language, defined once. For the underlying event-sourcing terms these build on — event, event source, read model, projection, reducer, reactor, observer — see the shared Cratis glossary; this page defines what is specific to Screenplay.

Structure

• .play file — a Screenplay source file. Describes one bounded context, top to bottom, in one declarative document.
• Module — the top-level namespace of a .play file; maps to a bounded context. One module per file by convention.
• Feature — a vertical grouping of related slices inside a module. Nests arbitrarily deep for sub-features.
• Slice — the atomic unit of behavior, aligned with Event Modeling. Has a type and a name and contains the constructs that implement one behavior.
• Construct — a declaration inside a slice: event, command, query, projection, capture, constraint, reactor, or screen.
• Offside rule — the indentation rule that defines structure: a construct owns everything indented beneath it. There are no braces.

Slice types

• StateChange — a command → events flow; something that changes the system.
• StateView — a query + projection + screen; something that reads the system.
• Automation — a reactor or reducer; something that reacts to events.
• Translate — a capture; converts external data into events.

Constructs

• Concept — a formalized value type that wraps a primitive (concept InvoiceId : Uuid) and carries compliance attributes; every usage inherits them.
• Policy — a named authorization rule (role-based, claim-based, or custom) that commands and queries reference by name via authorize.
• Command — an imperative intent with properties, authorize, validate, and a produces block declaring the events it appends.
• Event — a past-tense fact declaration: a named type and its properties.
• Query — a read-side entry point mapping identifying and filter parameters to a read-model return type (=> ReadModel[]).
• Projection — a declaration, written in PDL, that builds a read model by folding events (from EventType key ...).
• Capture — a declaration, written in CDL, that turns polled or pushed external data into events.
• Constraint — a server-side invariant (such as uniqueness) enforced in the Chronicle kernel before an event is committed.
• Reactor — a rule that observes events and produces side effects — notifications, follow-up events, or commands.
• Screen — a UI declaration inside a StateView slice, expressible at three levels from pure intent to layout with inline React.
• Layout — a reusable screen template with named slots, declared at module level and referenced by screens.

Sub-languages

• Sub-language — a named grammar embedded inside a construct’s body, parsed by a registered sub-parser. PDL and CDL are the built-ins; more can be registered.
• PDL (Projection Declaration Language) — the embedded sub-language for projection bodies.
• CDL (Change Data Capture Language) — the embedded sub-language for capture bodies.
• Embedded code block — an inline csharp, typescript, react, or html block (between triple backticks) or a file reference — the escape hatch any construct can drop into.
• Context variables — values the runtime supplies inside expressions: $context (event context), $env (environment), $eventContext, and $. (the current capture item).

Tools and runtime

• Stage — the runtime that interprets a .play file and runs it as a live application.
• Studio — the tool that reads the same .play file to visualize and generate.
• @cratis/screenplay-language — the Monaco language service: highlighting, completions, hover, and diagnostics for .play files.
• Screenplay editor — the standalone browser editor host that embeds the language service.
• Screenplay VS Code extension — the extension bringing the same language support to VS Code.