#version: openapi

-- schema.yaml --
components:
  schemas:
    User:
      description: "A User uses something."
      type: object
      properties:
        id:
          type: integer
        name:
          type: string
        address:
          allOf: [{$ref: "#/components/schemas/PhoneNumber"}]
          nullable: true
    PhoneNumber:
      description: "The number to dial."
      type: string

-- out/decode/extract --
// The number to dial.
#PhoneNumber: string

// A User uses something.
#User: {
	id?:   int
	name?: string
	address?:
		null | #PhoneNumber
	...
}
