Clarify roles of patternProperties/patternKeys vs propertyNames/keyNames

draft-vasters-json-structure-validation.md

@@ -364,10 +364,14 @@ Example:
 
 ### `patternProperties` and `patternKeys` {#patternProperties-and-patternKeys}
 
-This keyword applies schemas to properties whose names match specified regular
-expressions. For each property in the object instance, if its name matches a
-regular expression defined in `patternProperties`, then its value MUST validate
-against the corresponding schema. The property names used as keys in
+This keyword applies validation schemas to the **values** of properties whose
+names match specified regular expressions. It does not define or declare
+properties; rather, it constrains the values of any properties that happen to
+match the given patterns.
+
+For each property in the object instance, if its name matches a regular
+expression defined in `patternProperties`, then its value MUST validate against
+the corresponding schema. The property names used as keys in
 `patternProperties` MUST be strings representing valid regular expressions
 conforming to the {{ECMA_262_2022}} standard. The `patternKeys` keyword applies
 equivalently to `map` types.
@@ -389,10 +393,12 @@ Example:
 
 ### `propertyNames` and `keyNames` {#propertyNames-and-keyNames}
 
-The `propertyNames` keyword validates the names of all properties in an object
-against a `string`-typed schema. An object is valid if every property name in
-the object is valid. The schema MUST be of type `string`. The `keyNames` keyword
-applies equivalently to `map` types.
+The `propertyNames` keyword constrains the **names** of all properties in an
+object. Unlike `patternProperties`, which validates property values based on
+name patterns, `propertyNames` validates the names themselves against a
+`string`-typed schema. An object is valid only if every property name in the
+object satisfies the given schema. The schema MUST be of type `string`. The
+`keyNames` keyword applies equivalently to `map` types.
 
 Example: