According to https://swagger.io/specification/#fixed-fields-51 towards

the end of the section, a Parameter Object MUST contain either a
'schema' property or a 'content' property (but not both).

Author: jfinkhaeuser

openapi_spec_validator/resources/schemas/v3.0.0/schema.json

@@ -433,7 +433,15 @@
           "content": {
             "$ref": "#/definitions/mediaTypes"
           }
-        }
+        },
+        "oneOf": [
+          {
+            "required": [ "schema" ]
+          },
+          {
+            "required": [ "content" ]
+          }
+        ]
       },
       "requestBody": {
         "type": "object",
@@ -1250,4 +1258,4 @@
         ]
       }
     }
-  }
+  }