diff --git a/.gitignore b/.gitignore
index 4b26743a7..e22705bb4 100644
--- a/.gitignore
+++ b/.gitignore
@@ -17,6 +17,7 @@
 /docker/ubuntu20.04/src/
 
 # Temporary working dirs
+/oss
 /src-*
 /src_*
 
diff --git a/CONTRIBUTING.md b/CONTRIBUTING.md
index ca1ce81e4..c4ea7bb8d 100644
--- a/CONTRIBUTING.md
+++ b/CONTRIBUTING.md
@@ -2,7 +2,13 @@ Contributing Guide
 ==================
 
 ## Pull Requests
-**Mozc team is not accepting pull requests for files under src/.**
+**Pull requests to the Mozc project are limited to the specific directories.**
+
+Files and directories we may accept pull requests.
+* files in the top directory
+* docker/
+* docs/
+* src/data/test/quality_regression/test/
 
 Although Google company policy certainly allows Mozc team to accept pull
 requests, to do so Mozc team needs to move all Mozc source files into
diff --git a/PULL_REQUEST_TEMPLATE.md b/PULL_REQUEST_TEMPLATE.md
index a66d51077..490f46e24 100644
--- a/PULL_REQUEST_TEMPLATE.md
+++ b/PULL_REQUEST_TEMPLATE.md
@@ -1,4 +1,10 @@
-**Mozc team is not accepting pull requests for files under src/.**
+**Pull requests to the Mozc project are limited to the specific directories.**
+
+Files and directories we may accept pull requests.
+* files in the top directory
+* docker/
+* docs/
+* src/data/test/quality_regression/test/
 
 Although Google company policy certainly allows Mozc team to accept pull
 requests, to do so Mozc team needs to move all Mozc source files into
diff --git a/docs/configurations.md b/docs/configurations.md
new file mode 100644
index 000000000..6bca60135
--- /dev/null
+++ b/docs/configurations.md
@@ -0,0 +1,88 @@
+# Configurations
+
+## IBus
+
+IBus specific configurations are customizable in `~/.config/mozc/ibus_config.textproto`.
+
+The file path may be `~/.mozc/ibus_config.textproto` if `~/.mozc` directry already exists.
+
+
+Here is the default configuration.
+```
+engines {
+  name : "mozc-jp"
+  longname : "Mozc"
+  layout : "default"
+  layout_variant : ""
+  layout_option : ""
+  rank : 80
+}
+active_on_launch: False
+```
+
+The variables of `engines` are mapped to the same named variables of IBus.
+
+**Note:**
+After modification of `ibus_config.textproto`,
+`ibus write-cache; ibus restart` might be necessary to apply changes.
+
+
+### Specify the keyboard layout
+
+`layout` represents the keyboard layout (e.g. JIS keyboard, US keyboard, etc.).
+
+Sample configuration
+```
+engines {
+  name : "mozc-jp"
+  longname : "Mozc"
+  layout : "ja"  # or "us"
+  layout_variant : ""
+  layout_option : ""
+  rank : 80
+}
+active_on_launch: False
+```
+
+
+### Activate Mozc on launch
+
+`active_on_launch` represents the default input.
+If it's True, Hiragana input is the default mode.
+
+Sample configuration
+```
+engines {
+  name : "mozc-jp"
+  longname : "Mozc"
+  layout : "default"
+  layout_variant : ""
+  layout_option : ""
+  rank : 80
+}
+active_on_launch: True  # default is False.
+```
+
+### Multiple engines with different keyboard layouts
+
+`engines` can be multiple entries.
+
+```
+engines {
+  name : "mozc-jp"
+  longname : "Mozc"
+  layout : "ja"
+  layout_variant : ""
+  layout_option : ""
+  rank : 80
+}
+engines {
+  name : "mozc-us"
+  longname : "Mozc US"
+  layout : "us"
+  layout_variant : ""
+  layout_option : ""
+  rank : 80
+}
+active_on_launch: False
+```