documenting annotation.

doc/basics.md

@@ -23,6 +23,7 @@ separate document](https://github.com/simdjson/simdjson/blob/master/doc/builder.
   * [2. Use `tag_invoke` for custom types (C++20)](#2-use-tag_invoke-for-custom-types-c20)
   * [3. Using static reflection (C++26)](#3-using-static-reflection-c26)
     + [Special cases](#special-cases)
+    + [Renaming and skipping fields with annotations](#renaming-and-skipping-fields-with-annotations)
   * [The simdjson::from shortcut (experimental, C++20)](#the-simdjsonfrom-shortcut-experimental-c20)
 - [Minifying JSON strings without parsing](#minifying-json-strings-without-parsing)
 - [UTF-8 validation (alone)](#utf-8-validation-alone)
@@ -1592,6 +1593,49 @@ You can also automatically serialize the `Car` instance to a JSON string, see
 our [Builder documentation](builder.md).
 
 
+#### Renaming fields and skipping fields with annotations
+
+C++26 annotations provide a convenient way to customize (de)serialization
+without writing `tag_invoke` functions. You can rename the JSON key that
+corresponds to a C++ data member, or skip a member entirely.
+
+The syntax is:
+
+```cpp
+// rename cppFieldName (in C++) to json_key_name (in JSON)
+[[= simdjson::rename<"json_key_name">]] std::string cppFieldName;
+// do not serialize or deserialize this field
+[[= simdjson::skip]] int internalState;
+```
+
+Full examples:
+
+```cpp
+struct RenamedFields {
+  [[= simdjson::rename<"first_name">]] std::string firstName = "";
+  [[= simdjson::rename<"last_name">]]  std::string lastName = "";
+  int age = 0;
+};
+
+struct SkippedField {
+  std::string name = "";
+  [[= simdjson::skip]] int internalCache = 0;
+};
+
+struct MixedAnnotations {
+  [[= simdjson::rename<"user_name">]] std::string userName = "";
+  [[= simdjson::skip]] int sessionToken = 0;
+  int age = 0;
+};
+```
+
+- Serialization via `simdjson::to_json(r)` or `builder << r` will use the renamed
+  keys and omit skipped fields.
+- Deserialization via `doc.get<RenamedFields>()` will map the JSON keys back
+  to the C++ fields. Skipped fields are never written during deserialization
+  (they keep their default-initialized value), and keys matching skipped fields
+  in the JSON input are ignored.
+
 
 ### The simdjson::from shortcut (experimental, C++20)
 

doc/builder.md

@@ -12,6 +12,7 @@ speed and high convenience.
   * [Overview: string_builder](#overview--string-builder)
   * [Example: string_builder](#example--string-builder)
   * [C++26 static reflection](#c--26-static-reflection)
+    + [Renaming fields and skipping fields with annotations](#renaming-fields-and-skipping-fields-with-annotations)
     + [Without `string_buffer` instance](#without--string-buffer--instance)
     + [Without `string_buffer` instance but with explicit error handling](#without--string-buffer--instance-but-with-explicit-error-handling)
     + [Pretty formatted (fractured JSON)](#pretty-formatted-fractured-json)
@@ -260,6 +261,45 @@ automatically. In most cases, it should work automatically:
 ```
 
 
+#### Renaming fields and skipping fields with annotations
+
+When using C++26 static reflection for automatic serialization (and deserialization),
+you can annotate your struct members to rename the corresponding JSON keys or to
+exclude fields from the JSON representation.
+
+
+The syntax is:
+
+```cpp
+// rename cppFieldName (in C++) to json_key_name (in JSON)
+[[= simdjson::rename<"json_key_name">]] std::string cppFieldName;
+// do not serialize or deserialize this field
+[[= simdjson::skip]] int internalState;
+```
+
+For example:
+
+```cpp
+struct Person {
+    [[= simdjson::rename<"first_name">]] std::string firstName = "";
+    [[= simdjson::rename<"last_name">]]  std::string lastName = "";
+    [[= simdjson::skip]] int internalCache = 0;
+    int age = 0;
+};
+```
+
+Serialization then produces:
+
+```cpp
+Person p{"Alice", "Smith", 999, 30};
+std::string json = simdjson::to_json(p);
+// json == R"({"first_name":"Alice","last_name":"Smith","age":30})"
+// Note: internalCache is omitted entirely.
+```
+
+The `skip` annotation also affects deserialization: the field keeps its default value
+and any corresponding key in the input JSON is ignored.
+
 ### Without `string_buffer` instance
 
 In some instances, you might want to create a string directly from your own data type.