"The discriminator object is legal only when using one of the composite keywords oneOf, anyOf, allOf."

https://spec.openapis.org/oas/v3.1.0#fixed-fields-20

Author: karenetheridge

schemas/v3.1/meta/base.schema.json

@@ -22,7 +22,8 @@
                 "mapping": {
                     "type": "object",
                     "additionalProperties": {
-                        "type": "string"
+                        "type": "string",
+                        "format": "uri-reference"
                     }
                 }
             },
@@ -67,6 +68,15 @@
             },
             "unevaluatedProperties": false
     },
+    "dependentSchemas": {
+        "discriminator": {
+            "anyOf": [
+                { "required": [ "oneOf" ] },
+                { "required": [ "anyOf" ] },
+                { "required": [ "allOf" ] }
+            ]
+        }
+    },
     "$defs": {
         "extensible": {
             "patternProperties": {

schemas/v3.1/meta/base.schema.yaml

@@ -10,6 +10,7 @@ properties:
       mapping:
         additionalProperties:
           type: string
+          format: uri-reference
         type: object
       propertyName:
         type: string
@@ -47,6 +48,12 @@ properties:
         type: boolean
     type: object
     unevaluatedProperties: false
+dependentSchemas:
+  discriminator:
+    anyOf:
+    - required: [ oneOf ]
+    - required: [ anyOf ]
+    - required: [ allOf ]
 $dynamicAnchor: meta
 $id: https://spec.openapis.org/oas/3.1/meta/base
 $schema: https://json-schema.org/draft/2020-12/schema