diff --git a/docs/schema/index.md b/docs/schema/index.md
index 48f5005..c33a080 100644
--- a/docs/schema/index.md
+++ b/docs/schema/index.md
@@ -4,12 +4,13 @@
 
 ```shell
 <DATASET_ID>/
-└── <DATASET_VERSION>
-    ├── annotation    ...schema tables in JSON format
-    ├── data          ...sensor raw data
-    ├── input_bag     ...original ROS bag file
-    ├── map           ...map files
-    └── status.json   ...dataset status information
+└── <DATASET_VERSION>/
+    ├── annotation/    ...schema tables in JSON format
+    ├── data/          ...sensor raw data
+    ├── input_bag/     ...original ROS bag file
+    ├── map/           ...map files
+    ├── lidarseg/      ...[OPTIONAL] LiDAR segmentation annotation
+    └── status.json    ...dataset status information
 ```
 
 ## Schema Tables
@@ -32,8 +33,22 @@ It is structured as follows:
 
 ```shell
 map/
-├── lanelet2_map.osm
-└── pointcloud_map.pcd
+├── lanelet2_map.osm    ...lanelet2 map file
+└── pointcloud_map.pcd/ ...pointcloud map directory
+```
+
+## LiDAR Segmentation Annotation
+
+T4 dataset can include 3D LiDAR segmentation annotation optionally.
+The format is exactly the same as the [nuScenes format](https://www.nuscenes.org/nuscenes) with one additional `lidarseg.json` file.
+
+Note that every `<lidarseg_token>.bin` consists of category labels for every LiDAR pointcloud at a keyframe.
+
+```shell
+lidarseg/
+└── annotation/
+    ├── <lidarseg_token>.bin    ...category labels for every LiDAR pointcloud at a keyframe
+    ...
 ```
 
 ## status.json
diff --git a/mkdocs.yaml b/mkdocs.yaml
index 96cd127..6f27a33 100644
--- a/mkdocs.yaml
+++ b/mkdocs.yaml
@@ -64,27 +64,28 @@ plugins:
             - https://numpy.org/doc/stable/objects.inv
             - https://ipython.readthedocs.io/en/stable/objects.inv
           options:
-            # general
-            filters: ["!^_"]
-            show_bases: false
-            show_source: true
-            # headings
-            heading_level: 2
-            parameter_headings: false
-            show_root_heading: true
-            show_symbol_type_heading: true
-            show_symbol_type_toc: true
-            # members
-            inherited_members: false
-            members_order: source # The order of class members
-            # docstrings
-            docstring_style: google
-            docstring_section_style: list # list spacy table
-            merge_init_into_class: true
-            # signatures
-            separate_signature: true
-            show_signature_annotations: true
-            show_overload: true
+            extra:
+              # general
+              filters: ["!^_"]
+              show_bases: false
+              show_source: true
+              # headings
+              heading_level: 2
+              parameter_headings: false
+              show_root_heading: true
+              show_symbol_type_heading: true
+              show_symbol_type_toc: true
+              # members
+              inherited_members: false
+              members_order: source # The order of class members
+              # docstrings
+              docstring_style: google
+              docstring_section_style: list # list spacy table
+              merge_init_into_class: true
+              # signatures
+              separate_signature: true
+              show_signature_annotations: true
+              show_overload: true
 
 markdown_extensions:
   - pymdownx.highlight: