The none type accepts no values. Its schema is {"anyOf": []}: there are no alternatives a value can match. Reference it as {"type": "hm://hyper.media/none"}. It is a schema built from the existing union vocabulary, not a new data kind.

Unlike none, the null type and the bare literal schema null accept exactly one value: null. The any type accepts every Hypermedia value.

A list whose items schema is none can only be empty. A map whose values schema is none can only be empty. On a struct, values applies to additional fields, so setting it to none forbids fields outside properties. An optional field typed none must be absent; a required field typed none makes the struct impossible to satisfy.

The TypeScript generator emits HMNone = never. The type has no default value for editors to create. Its formal schema is attached as the schemaDefinition in this document's metadata.

See also

Union schema: a value must match at least one alternative.

Null: the type with exactly one value.

Any: the type that accepts every value.