Keywords

The language reserves two kinds of keys: every $-prefixed key, which is a keyword, and the two structural keys type and props. The dialect defines everything else: which element types exist, and which prop names appear inside props. The keywords fall into five groups.

Coupled keywords share a row: the first keyword governs the construct, and the ones after it are only valid alongside it.

Document

Identify a schema and its dialect:

Keyword	Purpose	Reference
`$id`	Identity and revision of a document	Documents
`$schema`	Dialect identifier of a document	Documents

Expressions

Resolve a value anywhere one is expected:

Keywords	Purpose	Reference
`$data`	Reference to a data field value	Data References
`$t` `$params` `$tags`	Reference to a translatable message, with interpolated values and tags	Translation References
`$message` `$params`	Inline ICU pattern to format, with interpolated values	Inline Messages
`$arg`	Reference to a scoped argument	Scoped Arguments

Actions

Dispatch handlers on callbacks:

Keywords	Purpose	Reference
`$action` `$args`	Handler to dispatch, with the arguments passed	Actions

Control Flow

Select or repeat a value:

Keywords	Purpose	Reference
`$if` `$matches` `$then` `$else`	Binary conditional, tested by schema validation	If/Then/Else
`$switch` `$case` `$default`	Multi-case conditional, discriminated by value	Switch/Case/Default
`$map` `$each`	Iteration, applying a template to each item of an array	Maps

Form Fields

Bind a prop to a data field:

Keyword	Purpose	Reference
`$field`	Two-way binding to a data field	Form Fields

$field appears in the same value positions as expressions, but it does more than read: it resolves a value and registers a two-way binding with form state. Every other value-position keyword is a pure read.