clarify other prohibited combinations of query+querystring

That is, these are also prohibited:

- "query" appearing in the path-item's parameters and "querystring" in
the operation's parameters
- "querystring" appearing in the path-item's parameters and "query" appearing
in the operation's parameters

Author: karenetheridge

src/oas.md

@@ -766,8 +766,8 @@ See [Appendix E](#appendix-e-percent-encoding-and-form-media-types) for a detail
 There are five possible parameter locations specified by the `in` field:
 
 * path - Used together with [Path Templating](#path-templating), where the parameter value is actually part of the operation's URL. This does not include the host or base path of the API. For example, in `/items/{itemId}`, the path parameter is `itemId`.
-* query - Parameters that are appended to the URL. For example, in `/items?id=###`, the query parameter is `id`; MUST NOT appear in the same operation as an `in: "querystring"` parameter.
-* querystring - A parameter that treats the entire URL query string as a value which MUST be specified using the `content` field, most often with media type `application/x-www-form-urlencoded` using [Encoding Objects](#encoding-object) in the same way as with request bodies of that media type; MUST NOT appear more than once, and MUST NOT appear in the same operation as any `in: "query"` parameters.
+* query - Parameters that are appended to the URL. For example, in `/items?id=###`, the query parameter is `id`; MUST NOT appear in the same operation (or in the operation's path-item) as an `in: "querystring"` parameter.
+* querystring - A parameter that treats the entire URL query string as a value which MUST be specified using the `content` field, most often with media type `application/x-www-form-urlencoded` using [Encoding Objects](#encoding-object) in the same way as with request bodies of that media type; MUST NOT appear more than once, and MUST NOT appear in the same operation (or in the operation's path-item) as any `in: "query"` parameters.
 * header - Custom headers that are expected as part of the request. Note that [RFC9110](https://www.rfc-editor.org/rfc/rfc9110.html#section-5.1) states header names are case insensitive.
 * cookie - Used to pass a specific cookie value to the API.