# `A2UICore.Schema`
[🔗](https://github.com/a2ui-elixir/a2ui/blob/v0.1.1/umbrella/apps/a2ui_core/lib/a2ui_core/schema.ex#L1)

JSON Schema **Draft 2020-12** validator used by A2UI's catalog,
envelope, and payload validation.

It implements the core, applicator, unevaluated and validation
vocabularies, and passes every required test of the official
[JSON Schema Test Suite](https://github.com/json-schema-org/JSON-Schema-Test-Suite)
for draft 2020-12.

References (`$ref`, `$dynamicRef`) resolve against the base URI that
`$id` sets, to JSON pointers (percent-encoded or not), `$anchor` and
`$dynamicAnchor` names, and embedded resources. A referenced document
is looked up in the registry by its resolved URI, by the reference as
written (the protocol schemas name `"common_types.json"`, and
`"catalog.json"` is a registry key the caller binds to the active
catalog), by its `$id`, and finally by URL basename.

A `$schema` naming a meta-schema in the registry that declares its
`$vocabulary` switches off the keywords of the standard vocabularies
it leaves out; a vocabulary it requires that this module does not know
raises `ArgumentError`. Listing the format-assertion vocabulary turns
on `formats: :assert`.

`pattern` and `patternProperties` are ECMA-262 regular expressions
(`A2UICore.Schema.ECMA262`).

Annotation-only keywords (allowed, never asserted): `title`,
`description`, `default`, `deprecated`, `x-deprecated-reason`,
`examples`, `readOnly`, `writeOnly`, `format` (unless `formats: :assert`),
`content*`, `discriminator`, `$schema`, `$id`, `$anchor`,
`$dynamicAnchor`, `$vocabulary`, `$comment`, `$defs`, and the catalog
fields `catalogId`, `instructions`, `protocolVersion`, `returnType`,
`allowedCallers`, `requiresUserActivation`, `allowedParents`,
`allowedChildren`, `metadata` and `components`/`functions` (catalog
containers, entered via `$ref` only).

# `registry`
*since 0.1.0* 

```elixir
@type registry() :: %{optional(String.t()) => schema()}
```

Registry mapping `$ref` document names/URLs to schema bodies.

# `schema`
*since 0.1.0* 

```elixir
@type schema() :: map() | boolean()
```

# `validate`
*since 0.1.0* 

```elixir
@spec validate(term(), schema(), keyword()) ::
  :ok | {:error, [A2UICore.Error.Detail.t()]}
```

Validates `data` against `schema`.

Options:

* `:registry` — map of `$ref` targets to document bodies; keys may be
  the reference's href (e.g. `"catalog.json"`, `"common_types.json"`)
  or an absolute URL (`"https://a2ui.org/.../common_types.json"`).
* `:root` — the document that local `#/...` `$ref`s resolve against
  (defaults to the registry entry keyed `"catalog.json"` when present,
  otherwise to `schema` itself).
* `:formats` — `:annotate` (default) treats `format` as an annotation,
  like the reference SDK's validator; `:assert` checks the formats the
  A2UI schemas use (`uri`, `date`, `time`, `date-time`) the way ajv with
  ajv-formats does in the upstream spec test runner.

Returns `:ok` on success, or `{:error, [Detail.t()]}`.

---

*Consult [api-reference.md](api-reference.md) for complete listing*