Issue - XML representation of response payload and request body

[hrennau]

In the OpenAPI spec, section "XML Object",
https://github.com/OAI/OpenAPI-Specification/blob/master/versions/3.0.2.md#xmlObject

implicitly defines default rules for the XML representation of JSON properties:

• an object property is represented by an XML element with a name equal property name
• an array value is represented by repeated XML elements, one for each array item, without wrapper element

The spec does not make statements about how XML elements representing a JSON root value (the value representing the response payload, or the request body) should be represented:

• choice of element name
• handling of a JSON root value which is an array

Note: a JSON array as root value obviously requires a wrapper XML element containing the item XML elements; so there are two element names to choose.

PROPOSAL
(1) Section "Schema object", table "Fixed Fields", row "xml":

The constraint
"This MAY be used only on properties schemas. It has no effect on root schemas. "
is modified so that XML objects CAN be used for root schemas defining request bodies and response payloads. These schemas can be found at the following (informal) JSON paths:
Response payload:
/paths/{path}/(get|post|put|delete|options|head|patch)/responses/({return-code}|default)/content/{mediatype}/schema
Request body:
/paths/{path}/(get|post|put|delete)/requestBody/content/{mediatype}/schema

(2) The spec includes a text defining default rules for the XML representation of response payloads and request bodies.

[handrews]

Closing as duplicate of #1435