diff --git a/.dir-locals.el b/.dir-locals.el
index 0cd7ee5..cafcbc6 100644
--- a/.dir-locals.el
+++ b/.dir-locals.el
@@ -1,5 +1,6 @@
 ;;; Directory Local Variables            -*- no-byte-compile: t -*-
 ;;; For more information see (info "(emacs) Directory Variables")
 
-((nil . ((eval . (progn (add-to-list 'grep-find-ignored-directories "tmp")
+((nil . ((eval . (progn (require 'grep)
+                        (add-to-list 'grep-find-ignored-directories "tmp")
                         (add-to-list 'grep-find-ignored-directories "doc"))))))
diff --git a/.github/workflows/doc.yaml b/.github/workflows/doc.yaml
new file mode 100644
index 0000000..65414e0
--- /dev/null
+++ b/.github/workflows/doc.yaml
@@ -0,0 +1,40 @@
+name: Build and deploy documentation to GitHub Pages
+on:
+  push:
+    branches: [ "main" ]
+  pull_request:
+  workflow_dispatch:
+
+jobs:
+  build-and-deploy:
+    runs-on: ubuntu-latest
+    steps:
+      - name: Checkout
+        uses: actions/checkout@v6
+
+      - name: Install Ruby
+        uses: ruby/setup-ruby@v1
+        with:
+          ruby-version: '3.4'
+          bundler-cache: true
+
+      - name: Run RDoc
+        run: rdoc
+
+      - name: Upload Pages artifact
+        uses: actions/upload-pages-artifact@v3
+        with:
+          path: doc
+
+  deploy:
+    needs: build-and-deploy
+    runs-on: ubuntu-latest
+    steps:
+      - name: Deploy to GitHub Pages
+        uses: actions/deploy-pages@v4
+    permissions:
+      id-token: write
+      pages: write
+    environment:
+      name: github-pages
+      url: ${{ steps.deployment.outputs.page_url }}
diff --git a/.rdoc_options b/.rdoc_options
index c5c5134..e9e85cf 100644
--- a/.rdoc_options
+++ b/.rdoc_options
@@ -4,3 +4,4 @@ exclude:
   - bin
   - Rakefile
   - Gemfile
+  - vendor
diff --git a/CHANGELOG.md b/CHANGELOG.md
index 90e97e6..7cda3b7 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,7 +1,10 @@
 # Change log of Ruby GettextPO gem
 
-## [Unreleased]
+## Unreleased
 
-## [0.1.0] - 2026-03-07
+- Add libgettextpo version constant.
+- Add severities constants.
+
+## 0.1.0 - 2026-03-07
 
 - Initial release
diff --git a/ext/gettextpo/gettextpo.c b/ext/gettextpo/gettextpo.c
index 8b1fc3e..9a0246d 100644
--- a/ext/gettextpo/gettextpo.c
+++ b/ext/gettextpo/gettextpo.c
@@ -17,29 +17,9 @@
 
 #include "gettextpo.h"
 #include <gettext-po.h>
-#include <ruby/internal/anyargs.h>
+#include <ruby.h>
 #include <ruby/internal/arithmetic/int.h>
-#include <ruby/internal/core/rdata.h>
-#include <ruby/internal/core/rstring.h>
-#include <ruby/internal/core/rtypeddata.h>
-#include <ruby/internal/eval.h>
-#include <ruby/internal/globals.h>
-#include <ruby/internal/intern/array.h>
-#include <ruby/internal/intern/hash.h>
-#include <ruby/internal/intern/object.h>
-#include <ruby/internal/intern/proc.h>
-#include <ruby/internal/intern/range.h>
-#include <ruby/internal/intern/string.h>
-#include <ruby/internal/intern/vm.h>
-#include <ruby/internal/module.h>
-#include <ruby/internal/scan_args.h>
-#include <ruby/internal/special_consts.h>
-#include <ruby/internal/symbol.h>
-#include <ruby/internal/value.h>
-#include <stdbool.h>
-#include <stddef.h>
-#include <stdlib.h>
-#include <time.h>
+#include <ruby/internal/variable.h>
 
 VALUE rb_cMessage;
 VALUE rb_cMessageIterator;
@@ -845,6 +825,14 @@ RUBY_FUNC_EXPORTED void
 Init_gettextpo (void)
 {
   VALUE rb_mGettextPO = rb_define_module ("GettextPO");
+  rb_define_const (rb_mGettextPO, "LIBGETTEXTPO_VERSION",
+                   INT2NUM (libgettextpo_version));
+  rb_define_const (rb_mGettextPO, "SEVERITY_WARNING",
+                   INT2NUM (PO_SEVERITY_WARNING));
+  rb_define_const (rb_mGettextPO, "SEVERITY_ERROR",
+                   INT2NUM (PO_SEVERITY_ERROR));
+  rb_define_const (rb_mGettextPO, "SEVERITY_FATAL_ERROR",
+                   INT2NUM (PO_SEVERITY_FATAL_ERROR));
   rb_define_singleton_method (rb_mGettextPO, "header_entry_value",
                               gettextpo_m_header_entry_value, 2);
   rb_define_singleton_method (rb_mGettextPO, "header_with_updated_entry_value",
diff --git a/test/gettextpo_test.rb b/test/gettextpo_test.rb
index e4edf0b..30f6c22 100644
--- a/test/gettextpo_test.rb
+++ b/test/gettextpo_test.rb
@@ -22,6 +22,8 @@ class GettextPOTest < Test::Unit::TestCase
     assert do
       ::GettextPO.const_defined?(:VERSION)
     end
+
+    assert_compare 2944, '<=', GettextPO::LIBGETTEXTPO_VERSION
   end
 
   test "GettextPO::File.new" do