diff --git a/CMakeLists.txt b/CMakeLists.txt
index 2686d95e..e65466a0 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -1130,6 +1130,7 @@ if(TINYUSDZ_BUILD_EXAMPLES)
   add_subdirectory(examples/tydra_api)
   add_subdirectory(examples/tydra_to_renderscene)
   add_subdirectory(examples/api_tutorial)
+  add_subdirectory(examples/file_format)
   if (TINYUSDZ_WITH_JSON)
     add_subdirectory(examples/usd_to_json)
   endif()
diff --git a/data/fileformat_my.usda b/data/fileformat_my.usda
new file mode 100644
index 00000000..c53b5b82
--- /dev/null
+++ b/data/fileformat_my.usda
@@ -0,0 +1,10 @@
+#usda 1.0
+
+# example USDA for fileformat example: "my" custom fileformat.
+def "muda" (
+	references = @bora.my@
+	)
+{
+
+}
+
diff --git a/examples/file_format/CMakeLists.txt b/examples/file_format/CMakeLists.txt
new file mode 100644
index 00000000..6800be66
--- /dev/null
+++ b/examples/file_format/CMakeLists.txt
@@ -0,0 +1,15 @@
+# Assume this cmake is called from tinyusdz root(../../)
+set(EXAMPLE_TARGET "file_format_example")
+
+set(TINYUSDZ_API_TUTORIAL_SOURCES
+    file-format-example.cc
+    )
+
+add_executable(${EXAMPLE_TARGET} ${TINYUSDZ_API_TUTORIAL_SOURCES})
+add_sanitizers(${EXAMPLE_TARGET})
+
+target_include_directories(${EXAMPLE_TARGET} PRIVATE ${PROJECT_SOURCE_DIR}/src)
+target_link_libraries(${EXAMPLE_TARGET} tinyusdz_static)
+
+
+set_target_properties(${EXAMPLE_TARGET} PROPERTIES RUNTIME_OUTPUT_DIRECTORY "${CMAKE_BINARY_DIR}")
diff --git a/examples/file_format/file-format-example.cc b/examples/file_format/file-format-example.cc
new file mode 100644
index 00000000..b784f031
--- /dev/null
+++ b/examples/file_format/file-format-example.cc
@@ -0,0 +1,104 @@
+// All-in-one TinyUSDZ core
+#include "tinyusdz.hh"
+
+// Import to_string() and operator<< features
+#include <iostream>
+#include "pprinter.hh"
+#include "value-pprint.hh"
+#include "prim-pprint.hh"
+
+// Tydra is a collection of APIs to access/convert USD Prim data
+// (e.g. Can get Attribute by name)
+// See <tinyusdz>/examples/tydra_api for more Tydra API examples.
+#include "tydra/scene-access.hh"
+
+std::map<std::string, float> g_map;
+
+//
+// custom File-format APIs.
+//
+static bool MyCheck(const tinyusdz::AssetInfo &asset, std::string *warn, std::string *err, void *user_data) {
+  return true;
+}
+
+static bool MyRead(const  tinyusdz::AssetInfo &asset, tinyusdz::PrimSpec &ps/* inout */, std::string *warn, std::string *err, void *user_data) {
+  std::string key = asset.identifier.GetAssetPath();
+
+  if (g_map.count(key)) {
+    float val = g_map[key];
+
+    tinyusdz::Attribute attr;
+    attr.set_value(val);
+    attr.set_name("myval");
+    attr.variability() = tinyusdz::Variability::Uniform;
+
+    ps.props()["myval"] = tinyusdz::Property(attr, /* custom */false);
+
+    return true;
+
+  } else {
+    if (err) {
+      (*err) += "`" + key + "` not found.\n";
+    }
+    return false;
+  }
+}
+
+static bool MyWrite(const  tinyusdz::AssetInfo &asset, const tinyusdz::PrimSpec &ps, std::string *err, void *user_data) {
+  // TOOD
+  return false;
+}
+
+
+int main(int argc, char **argv) {
+  g_map["bora"] = 3.14f;
+  g_map["dora"] = 6.14f;
+
+  tinyusdz::FileFormatHandler my_handler;
+  my_handler.extension = "my";
+  my_handler.description = "Custom fileformat  example.";
+  my_handler.checker = MyCheck;
+  my_handler.reader= MyRead;
+  my_handler.writer = MyWrite;
+  my_handler.userdata = nullptr;
+
+  tinyusdz::USDLoadOptions options;
+  options.fileformats["my"] = my_handler;
+
+  tinyusdz::Stage stage;  // empty scene
+
+  std::string input_usd_filepath = "../data/fileformat_my.usda";
+  if (argc > 1) {
+    input_usd_filepath = argv[1];
+  }
+
+  std::string warn, err;
+
+  tinyusdz::Layer layer;
+  bool ret = tinyusdz::LoadLayerFromFile(input_usd_filepath, &layer, &warn, &err, options);
+
+  if (warn.size()) {
+    std::cout << "WARN: " << warn << "\n";
+  }
+
+  if (!ret) {
+    std::cerr << err << "\n";
+    exit(-1);
+  }
+
+  // dummy Asset resolver.
+  tinyusdz::AssetResolutionResolver resolver;
+
+  // Do `references` composition to materialize `references = @***.my@`
+  tinyusdz::Layer composited_layer;
+  if (!tinyusdz::CompositeReferences(resolver, layer, &composited_layer, &warn, &err)) {
+    std::cerr << "Failed to composite `references`: " << err << "\n";
+    return -1;
+  }
+  
+ 
+  // Print USD scene as Ascii.
+  std::cout << composited_layer << "\n";
+
+  return EXIT_SUCCESS;
+}
diff --git a/src/tinyusdz.hh b/src/tinyusdz.hh
index 727f3254..6bf96102 100644
--- a/src/tinyusdz.hh
+++ b/src/tinyusdz.hh
@@ -98,7 +98,7 @@ struct FileFormatHandler
   FileFormatCheckFunction checker{nullptr};
   FileFormatReadFunction reader{nullptr};
   FileFormatWriteFunction writer{nullptr};
-  void *_userdata{nullptr};
+  void *userdata{nullptr};
 };
 
 struct USDLoadOptions {
@@ -153,7 +153,7 @@ struct USDLoadOptions {
 
   ///
   /// User-defined fileformat hander.
-  /// key = file(asset) extension.
+  /// key = file(asset) extension(`.` excluded. example: 'mtlx', 'obj').
   ///
   std::map<std::string, FileFormatHandler> fileformats;