merge.yaml

openapi: 3.0.1
info:
  title: Yeah
  description: Foobar
  version: "1.0.0"
servers:
  - url: https://example.com

paths:
  /foo:
    post:
      operationId: foo-post
      requestBody:
        content:
          application/json:
            schema:
              $ref: "#/components/schemas/SomeSchema"
          application/xml:
            schema:
              $ref: "#/components/schemas/SomeOtherSchema"
        required: true
      responses:
        "201":
          description: "201"
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/SomeSchema"
            application/xml:
              schema:
                $ref: "#/components/schemas/SomeOtherSchema"
        "200":
          description: "200"
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/SomeSchema"
            application/xml:
              schema:
                $ref: "#/components/schemas/SomeOtherSchema"
        "5XX":
          description: "5XX"
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/SomeSchema"
            application/xml:
              schema:
                $ref: "#/components/schemas/SomeOtherSchema"
        "4XX":
          description: "4XX"
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/SomeSchema"
            application/xml:
              schema:
                $ref: "#/components/schemas/SomeOtherSchema"
        "404":
          description: "Not found"         
        default:
          description: "You do not have necessary permissions for the resource"
          content:
            application/json:
              schema:
                $ref: "#/components/schemas/SomeSchema"

components:
  schemas:
    SomeSchemaEnum:
      type: string
      enum:
        - email
        - phone
    SomeSchemaBase:
      properties:
        type:
          allOf:
            - $ref: "#/components/schemas/SomeSchemaEnum"
        value:
          type: string
          maxLength: 255
      required:
        - type
    SomeSchema:
      allOf:
        - $ref: "#/components/schemas/SomeSchemaBase"        
        - type: object
          properties:
            schemas:
              - $ref: "#/components/schemas/SomeSchema"
        - type: object
          required:
            - value
    SomeOtherSchema:
      # yes, empty objects are valid
      type: object