allow for x- properties

Author: gregsdennis

specs/meta/meta.json

@@ -146,6 +146,9 @@
             "$comment": "Proposed keyword: https://github.com/json-schema-org/json-schema-spec/blob/main/specs/proposals/propertyDependencies.md"
         }
     },
+    "patternProperties": {
+        "^x-": true
+    },
     "$defs": {
         "anchorString": {
             "type": "string",