add comment to explain the code block

Author: lucy66hw

modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/ProtobufSchemaCodegen.java

@@ -1053,6 +1053,21 @@ public GeneratorLanguage generatorLanguage() {
         return GeneratorLanguage.PROTOBUF;
     }
 
+
+/**
+ * Handles additionalProperties defined in composed schemas (e.g., allOf) by injecting into the model's properties.
+ * Example:
+ *  components:
+ *    schemas:
+ *      Dog:
+ *        allOf:
+ *          - $ref: '#/components/schemas/DogBase'
+ *          - type: object
+ *            additionalProperties:
+ *              title: pet
+ *              $ref: '#/components/schemas/Pet'
+ * In this case, the second allOf that defines a map with string keys and Pet values will be part of model's property.
+ */
     @Override
     protected void addProperties(Map<String, Schema> properties, List<String> required, Schema schema, Set<Schema> visitedSchemas){
         super.addProperties(properties, required, schema, visitedSchemas);
@@ -1072,5 +1087,4 @@ protected void addProperties(Map<String, Schema> properties, List<String> requir
             properties.put(addtionalPropertiesName, schema);
         }
     }
-
 }