diff --git a/.travis.yml b/.travis.yml
index ebede58..0159545 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,3 +1,7 @@
 language: crystal
+
 script:
-  - scripts/test
+- bin/test
+
+after_success:
+- if [ "$TRAVIS_BRANCH" == "master" ]; then bin/deploy_doc; fi
diff --git a/bin/deploy_doc b/bin/deploy_doc
new file mode 100755
index 0000000..7ae8d53
--- /dev/null
+++ b/bin/deploy_doc
@@ -0,0 +1,65 @@
+#!/usr/bin/env ruby
+require "yaml"
+require "tmpdir"
+
+VERSION = /^refs\/tags\/v(\d+(\.\d+)*)$/
+
+Dir.mktmpdir do |dir|
+  cred_file = File.join(dir, ".git-credentials")
+  `touch #{cred_file}`
+  `chmod 600 #{cred_file}`
+  File.write cred_file, "https://mosop:#{ENV["MOSOP_GITHUB_ACCESS_TOKEN"]}@github.com\n"
+  Dir.mktmpdir do |dir|
+    Dir.chdir(dir) do
+      `git init`
+      `git config --local credential.helper 'store --file #{cred_file}'`
+      `git remote add origin https://github.com/mosop/optarg.git`
+      gh_pages_found = false
+      versions = []
+      `git ls-remote`.chomp.split("\n").each do |line|
+        sha, ref = line.split(/\s+/)
+        if VERSION =~ ref
+          versions << Gem::Version.new($1)
+        elsif ref == "refs/heads/gh-pages"
+          gh_pages_found = true
+        end
+      end
+      version = versions.sort.last
+      exit unless version
+      `git fetch origin v#{version}:tags/v#{version}`
+      `git checkout -b latest v#{version}`
+      `crystal deps`
+      `crystal doc`
+      doc_dir = File.join(dir, "doc")
+      Dir.mktmpdir do |dir|
+        Dir.chdir(dir) do
+          ver_dir = File.join(dir, "v#{version}")
+          if gh_pages_found
+            `git init`
+            `git config --local credential.helper 'store --file #{cred_file}'`
+            `git remote add origin https://github.com/mosop/optarg.git`
+            `git pull origin gh-pages`
+            `git checkout -b gh-pages origin/gh-pages`
+            Dir.glob("*") do |f|
+              `rm -rf #{f}` unless f.start_with?("v")
+            end
+            `rm -rf .git`
+          end
+          `cp -a #{doc_dir}/* #{dir}/`
+          `rm -rf #{ver_dir}`
+          `mkdir -p #{ver_dir}`
+          `cp -a #{doc_dir}/* #{ver_dir}/`
+          `git init`
+          `git config --local credential.helper 'store --file #{cred_file}'`
+          `git remote add origin https://github.com/mosop/optarg.git`
+          `git config --add --local user.name mosop`
+          `git config --add --local user.email mosop@users.noreply.github.com`
+          `git checkout -b gh-pages`
+          `git add .`
+          `git commit -m '#{Time.now.strftime("%Y%m%d")}'`
+          `git push -f origin gh-pages`
+        end
+      end
+    end
+  end
+end
diff --git a/scripts/test b/bin/test
similarity index 100%
rename from scripts/test
rename to bin/test
diff --git a/shard.yml b/shard.yml
index 312156b..fa00946 100644
--- a/shard.yml
+++ b/shard.yml
@@ -1,5 +1,5 @@
 name: optarg
-version: 0.5.0
+version: 0.5.1
 
 authors:
   - mosop
@@ -11,4 +11,4 @@ crystal: 0.20.5
 dependencies:
   callback:
     github: mosop/callback
-    version: ~> 0.6.0
+    version: ~> 0.6.1
diff --git a/spec/classes/argument_value_container_spec.cr b/spec/classes/argument_value_container_spec.cr
index 3f84e34..a8c6817 100644
--- a/spec/classes/argument_value_container_spec.cr
+++ b/spec/classes/argument_value_container_spec.cr
@@ -6,7 +6,7 @@ module OptargArgumentValueContainerClassFeature
 
   it "#[]" do
     model = Model.new(%w())
-    model.parser.parsed_args << "arg"
+    model.__parser.parsed_args << "arg"
     model[0].should eq "arg"
   end
 
diff --git a/spec/features/argument_array_spec.cr b/spec/features/argument_array_spec.cr
index 269e8ec..5b9935e 100644
--- a/spec/features/argument_array_spec.cr
+++ b/spec/features/argument_array_spec.cr
@@ -10,6 +10,5 @@ module OptargArgumentArrayFeature
     result = Model.parse(%w(foo bar baz))
     result.arg.should eq "foo"
     result.item.should eq ["bar", "baz"]
-    result.parsed_args.should eq %w(foo bar baz)
   end
 end
diff --git a/spec/features/detail/argument_value_container_spec.cr b/spec/features/detail/argument_value_container_spec.cr
deleted file mode 100644
index 4a4b5f4..0000000
--- a/spec/features/detail/argument_value_container_spec.cr
+++ /dev/null
@@ -1,15 +0,0 @@
-require "../../spec_helper"
-
-module OptargArgumentValueContainerFeatureDetail
-  class Model < Optarg::Model
-  end
-
-  it name do
-    result = Model.parse(%w(foo bar baz))
-    result.nameless_args.size.should eq 3
-    result.nameless_args[0].should eq "foo"
-    result.nameless_args[1].should eq "bar"
-    result.nameless_args[2].should eq "baz"
-    result.nameless_args.map{|i| "#{i}!"}.should eq %w(foo! bar! baz!)
-  end
-end
diff --git a/spec/features/detail/avoiding_overriding_methods_spec.cr b/spec/features/detail/avoiding_overriding_methods_spec.cr
deleted file mode 100644
index d774d0d..0000000
--- a/spec/features/detail/avoiding_overriding_methods_spec.cr
+++ /dev/null
@@ -1,13 +0,0 @@
-require "../../spec_helper"
-
-module OptargAvoidingOverridingMethodsFeatureDetail
-  class Model < Optarg::Model
-    string "--class"
-  end
-
-  it name do
-    result = Model.parse(%w(--class foo))
-    result.class.should eq Model
-    result[String]["--class"].should eq "foo"
-  end
-end
diff --git a/spec/features/detail/bool_option_value_accessor_spec.cr b/spec/features/detail/bool_option_value_accessor_spec.cr
deleted file mode 100644
index 3018026..0000000
--- a/spec/features/detail/bool_option_value_accessor_spec.cr
+++ /dev/null
@@ -1,15 +0,0 @@
-require "../../spec_helper"
-
-module OptargBoolOptionValueAccessorFeatureDetail
-  class Model < Optarg::Model
-    bool "-b"
-  end
-
-  it name do
-    result = Model.parse(%w(-b))
-    result.b?.should be_true
-
-    not_set = Model.parse(%w())
-    not_set.b?.should be_false
-  end
-end
diff --git a/spec/features/detail/named_argument_value_accessor_spec.cr b/spec/features/detail/named_argument_value_accessor_spec.cr
deleted file mode 100644
index 51d84b4..0000000
--- a/spec/features/detail/named_argument_value_accessor_spec.cr
+++ /dev/null
@@ -1,14 +0,0 @@
-require "../../spec_helper"
-
-module OptargNamedArgumentValueAccessorFeatureDetail
-  class Model < Optarg::Model
-    arg "arg1"
-    arg "arg2"
-  end
-
-  it name do
-    result = Model.parse(%w(foo bar))
-    result.arg1.should eq "foo"
-    result.arg2.should eq "bar"
-  end
-end
diff --git a/spec/features/detail/named_argument_value_hash_spec.cr b/spec/features/detail/named_argument_value_hash_spec.cr
deleted file mode 100644
index 5834c72..0000000
--- a/spec/features/detail/named_argument_value_hash_spec.cr
+++ /dev/null
@@ -1,13 +0,0 @@
-require "../../spec_helper"
-
-module OptargNamedArgumentValueHashFeatureDetail
-  class Model < Optarg::Model
-    arg "named"
-  end
-
-  it name do
-    result = Model.parse(%w(foo bar baz))
-    expected = {"named" => "foo"}
-    result[String].should eq expected
-  end
-end
diff --git a/spec/features/detail/nameless_argument_value_hash_spec.cr b/spec/features/detail/nameless_argument_value_hash_spec.cr
deleted file mode 100644
index 8be14c4..0000000
--- a/spec/features/detail/nameless_argument_value_hash_spec.cr
+++ /dev/null
@@ -1,13 +0,0 @@
-require "../../spec_helper"
-
-module OptargNamelessArgumentValueHashFeatureDetail
-  class Model < Optarg::Model
-    arg "named"
-  end
-
-  it name do
-    result = Model.parse(%w(foo bar baz))
-    expected = %w(bar baz)
-    result.nameless_args.should eq expected
-  end
-end
diff --git a/spec/features/detail/option_value_container_spec.cr b/spec/features/detail/option_value_container_spec.cr
deleted file mode 100644
index f39b47c..0000000
--- a/spec/features/detail/option_value_container_spec.cr
+++ /dev/null
@@ -1,31 +0,0 @@
-require "../../spec_helper"
-
-module OptargOptionValueContainerFeatureDetail
-  class Model < Optarg::Model
-    string "-s"
-    bool "-b"
-    array "-a"
-  end
-
-  it name do
-    result = Model.parse(%w(-s foo -b -a bar -a baz))
-    s = {"-s" => "foo"}
-    b = {"-b" => true}
-    a = {"-a" => ["bar", "baz"]}
-    result[String].should eq s
-    result[Bool].should eq b
-    result[Array(String)].should eq a
-  end
-
-  module KeyForMultipleName
-    class Model < Optarg::Model
-      bool %w(-f --force)
-    end
-
-    it name do
-      result = Model.parse(%w(--force))
-      result[Bool]["-f"].should be_true
-      expect_raises(KeyError) { result[Bool]["--force"] }
-    end
-  end
-end
diff --git a/spec/features/detail/parsed_argument_value_array_spec.cr b/spec/features/detail/parsed_argument_value_array_spec.cr
deleted file mode 100644
index b2cc2d8..0000000
--- a/spec/features/detail/parsed_argument_value_array_spec.cr
+++ /dev/null
@@ -1,13 +0,0 @@
-require "../../spec_helper"
-
-module OptargParsedArgumentValueArrayFeatureDetail
-  class Model < Optarg::Model
-    arg "named"
-  end
-
-  it name do
-    result = Model.parse(%w(foo bar baz))
-    expected = %w(foo bar baz)
-    result.parsed_args.should eq expected
-  end
-end
diff --git a/spec/features/detail/string_array_option_value_accessor_spec.cr b/spec/features/detail/string_array_option_value_accessor_spec.cr
deleted file mode 100644
index 080113a..0000000
--- a/spec/features/detail/string_array_option_value_accessor_spec.cr
+++ /dev/null
@@ -1,12 +0,0 @@
-require "../../spec_helper"
-
-module OptargStringArrayOptionValueAccessorFeatureDetail
-  class Model < Optarg::Model
-    array "-a"
-  end
-
-  it name do
-    result = Model.parse(%w(-a foo -a bar -a baz))
-    result.a.should eq %w(foo bar baz)
-  end
-end
diff --git a/spec/features/detail/string_option_value_accessor_spec.cr b/spec/features/detail/string_option_value_accessor_spec.cr
deleted file mode 100644
index 6ea9c2e..0000000
--- a/spec/features/detail/string_option_value_accessor_spec.cr
+++ /dev/null
@@ -1,16 +0,0 @@
-require "../../spec_helper"
-
-module OptargStringOptionValueAccessorFeatureDetail
-  class Model < Optarg::Model
-    string "-s"
-  end
-
-  it name do
-    result = Model.parse(%w(-s value))
-    result.s.should eq "value"
-
-    not_set = Model.parse(%w())
-    expect_raises(KeyError) { not_set.s }
-    not_set.s?.should be nil
-  end
-end
diff --git a/spec/features/detail/unparsed_argument_value_array_spec.cr b/spec/features/detail/unparsed_argument_value_array_spec.cr
deleted file mode 100644
index 343e82a..0000000
--- a/spec/features/detail/unparsed_argument_value_array_spec.cr
+++ /dev/null
@@ -1,13 +0,0 @@
-require "../../spec_helper"
-
-module OptargUnparsedArgumentValueArrayFeatureDetail
-  class Model < Optarg::Model
-    arg "stopper", stop: true
-  end
-
-  it name do
-    result = Model.parse(%w(foo bar baz))
-    expected = %w(bar baz)
-    result.unparsed_args.should eq expected
-  end
-end
diff --git a/spec/features/named_arguments_spec.cr b/spec/features/named_arguments_spec.cr
index 87f0981..a87d971 100644
--- a/spec/features/named_arguments_spec.cr
+++ b/spec/features/named_arguments_spec.cr
@@ -10,7 +10,6 @@ module OptargNamedArgumentsFeature
     result = Model.parse(%w(/path/to/src /path/to/build and more))
     result.src_dir.should eq "/path/to/src"
     result.build_dir.should eq "/path/to/build"
-    result.parsed_args.should eq ["/path/to/src", "/path/to/build", "and", "more"]
     result[String].should eq({"src_dir" => "/path/to/src", "build_dir" => "/path/to/build"})
     result.nameless_args.should eq ["and", "more"]
   end
diff --git a/spec/fix/inherit_definition_spec.cr b/spec/fix/inherit_definition_spec.cr
index ff4129c..28459af 100644
--- a/spec/fix/inherit_definition_spec.cr
+++ b/spec/fix/inherit_definition_spec.cr
@@ -13,31 +13,31 @@ module OptargFixInheritDefinitionFeature
   end
 
   it name do
-    Sub.definitions.all.size.should eq 5
-    Sub.definitions.arguments.size.should eq 1
-    Sub.definitions.options.size.should eq 3
-    Sub.definitions.value_options.size.should eq 2
-    Sub.definitions.values.size.should eq 3
-    Sub.definitions.handlers.size.should eq 1
-    Sub.definitions.terminators.size.should eq 1
-    Sub.definitions.argument_list.size.should eq 1
+    Sub.__klass.definitions.all.size.should eq 5
+    Sub.__klass.definitions.arguments.size.should eq 1
+    Sub.__klass.definitions.options.size.should eq 3
+    Sub.__klass.definitions.value_options.size.should eq 2
+    Sub.__klass.definitions.values.size.should eq 3
+    Sub.__klass.definitions.handlers.size.should eq 1
+    Sub.__klass.definitions.terminators.size.should eq 1
+    Sub.__klass.definitions.argument_list.size.should eq 1
 
-    Sub.definitions.all["arg"]?.should_not be_nil
-    Sub.definitions.all["-s"]?.should_not be_nil
-    Sub.definitions.all["-b"]?.should_not be_nil
-    Sub.definitions.all["-h"]?.should_not be_nil
-    Sub.definitions.all["--"]?.should_not be_nil
-    Sub.definitions.arguments["arg"]?.should_not be_nil
-    Sub.definitions.options["-s"]?.should_not be_nil
-    Sub.definitions.options["-b"]?.should_not be_nil
-    Sub.definitions.options["-h"]?.should_not be_nil
-    Sub.definitions.value_options["-s"]?.should_not be_nil
-    Sub.definitions.value_options["-b"]?.should_not be_nil
-    Sub.definitions.values["arg"]?.should_not be_nil
-    Sub.definitions.values["-s"]?.should_not be_nil
-    Sub.definitions.values["-b"]?.should_not be_nil
-    Sub.definitions.handlers["-h"]?.should_not be_nil
-    Sub.definitions.terminators["--"]?.should_not be_nil
-    Sub.definitions.argument_list[0]?.should_not be_nil
+    Sub.__klass.definitions.all["arg"]?.should_not be_nil
+    Sub.__klass.definitions.all["-s"]?.should_not be_nil
+    Sub.__klass.definitions.all["-b"]?.should_not be_nil
+    Sub.__klass.definitions.all["-h"]?.should_not be_nil
+    Sub.__klass.definitions.all["--"]?.should_not be_nil
+    Sub.__klass.definitions.arguments["arg"]?.should_not be_nil
+    Sub.__klass.definitions.options["-s"]?.should_not be_nil
+    Sub.__klass.definitions.options["-b"]?.should_not be_nil
+    Sub.__klass.definitions.options["-h"]?.should_not be_nil
+    Sub.__klass.definitions.value_options["-s"]?.should_not be_nil
+    Sub.__klass.definitions.value_options["-b"]?.should_not be_nil
+    Sub.__klass.definitions.values["arg"]?.should_not be_nil
+    Sub.__klass.definitions.values["-s"]?.should_not be_nil
+    Sub.__klass.definitions.values["-b"]?.should_not be_nil
+    Sub.__klass.definitions.handlers["-h"]?.should_not be_nil
+    Sub.__klass.definitions.terminators["--"]?.should_not be_nil
+    Sub.__klass.definitions.argument_list[0]?.should_not be_nil
   end
 end
diff --git a/spec/internal/argument_display_name_spec.cr b/spec/internal/argument_display_name_spec.cr
index 237619c..ea56af7 100644
--- a/spec/internal/argument_display_name_spec.cr
+++ b/spec/internal/argument_display_name_spec.cr
@@ -21,8 +21,8 @@ module OptargInternalArugmentDisplayNameFeature
   end
 
   it name do
-    Model.definitions.arguments["arg"].metadata.display_name.should eq "arg"
-    Upcase.definitions.arguments["arg"].metadata.display_name.should eq "ARG"
-    Upcase.definitions.options["--option"].metadata.display_name.should eq "--option"
+    Model.__klass.definitions.arguments["arg"].metadata.display_name.should eq "arg"
+    Upcase.__klass.definitions.arguments["arg"].metadata.display_name.should eq "ARG"
+    Upcase.__klass.definitions.options["--option"].metadata.display_name.should eq "--option"
   end
 end
diff --git a/spec/internal/raise_unknown_option_if_concatenated_options_not_matched_spec.cr b/spec/internal/raise_unknown_option_if_concatenated_options_not_matched_spec.cr
index 2e3a420..3ba9e69 100644
--- a/spec/internal/raise_unknown_option_if_concatenated_options_not_matched_spec.cr
+++ b/spec/internal/raise_unknown_option_if_concatenated_options_not_matched_spec.cr
@@ -6,6 +6,6 @@ module OptargInternalRaiseUnknownOptionIfConcatenatedOptionsNotMatchedFeature
 
   it name do
     model = Model.new(%w(-ab))
-    expect_raises(Optarg::UnknownOption, Optarg::UnknownOption.new(model.__parser, "-a").message) { model.parse }
+    expect_raises(Optarg::UnknownOption, Optarg::UnknownOption.new(model.__parser, "-a").message) { model.__parse }
   end
 end
diff --git a/spec/internal/raise_unsupported_concatenation_spec.cr b/spec/internal/raise_unsupported_concatenation_spec.cr
index 1f6e8aa..9787ec2 100644
--- a/spec/internal/raise_unsupported_concatenation_spec.cr
+++ b/spec/internal/raise_unsupported_concatenation_spec.cr
@@ -8,6 +8,6 @@ module OptargInternalRaiseUnsupportedConcatenationFeature
 
   it name do
     model = Model.new(%w(-sa))
-    expect_raises(Optarg::UnsupportedConcatenation, Optarg::UnsupportedConcatenation.new(model.__parser, Model.definitions.options["-s"]).message) { model.__parse}
+    expect_raises(Optarg::UnsupportedConcatenation, Optarg::UnsupportedConcatenation.new(model.__parser, Model.__klass.definitions.options["-s"]).message) { model.__parse}
   end
 end
diff --git a/spec/internal/required_argument_error_preserves_object_spec.cr b/spec/internal/required_argument_error_preserves_object_spec.cr
index ce6c29e..64dbf35 100644
--- a/spec/internal/required_argument_error_preserves_object_spec.cr
+++ b/spec/internal/required_argument_error_preserves_object_spec.cr
@@ -13,6 +13,6 @@ module OptargInternalRequiredArgumentErrorPreservesObjectFeature
       error = ex
     ensure
     end
-    error.as(Optarg::Definitions::StringArgument::Validations::Existence::Error).definition.should be Model.definitions.arguments["arg1"]
+    error.as(Optarg::Definitions::StringArgument::Validations::Existence::Error).definition.should be Model.__klass.definitions.arguments["arg1"]
   end
 end
diff --git a/spec/internal_spec.cr b/spec/internal_spec.cr
index 3996dbc..ca0a30e 100644
--- a/spec/internal_spec.cr
+++ b/spec/internal_spec.cr
@@ -15,14 +15,14 @@ module OptargInternalFeature
     result.s.should eq "v"
     result.s?.should eq "v"
     result.b?.should be_true
-    result.parsed_args.should eq %w(arg parsed)
+    result.__parser.parsed_args.should eq %w(arg parsed)
     result[String].should eq({"-s" => "v", "arg" => "arg"})
     result.nameless_args.should eq %w(parsed)
     result.unparsed_args.should eq %w(unparsed)
-    result.__parsed_nodes[0].should eq Optarg::Parser.new_node(%w(-s v), ParseModel.definitions.options["-s"])
-    result.__parsed_nodes[1].should eq Optarg::Parser.new_node(%w(-b), ParseModel.definitions.options["-b"])
-    result.__parsed_nodes[2].should eq Optarg::Parser.new_node(%w(arg), ParseModel.definitions.arguments["arg"])
-    result.__parsed_nodes[3].should eq Optarg::Parser.new_node(%w(parsed))
+    result.__parser.parsed_nodes[0].should eq Optarg::Parser.new_node(%w(-s v), ParseModel.__klass.definitions.options["-s"])
+    result.__parser.parsed_nodes[1].should eq Optarg::Parser.new_node(%w(-b), ParseModel.__klass.definitions.options["-b"])
+    result.__parser.parsed_nodes[2].should eq Optarg::Parser.new_node(%w(arg), ParseModel.__klass.definitions.arguments["arg"])
+    result.__parser.parsed_nodes[3].should eq Optarg::Parser.new_node(%w(parsed))
   end
 
   it "parses nothing" do
@@ -32,9 +32,9 @@ module OptargInternalFeature
     result.s?.should be_nil
     result.b?.should be_false
     result.nameless_args.should eq %w()
-    result.parsed_args.should eq %w()
+    result.__parser.parsed_args.should eq %w()
     result.unparsed_args.should eq %w()
-    result.__parsed_nodes.should eq [] of Array(String)
+    result.__parser.parsed_nodes.should eq [] of Array(String)
   end
 
   class Supermodel < Optarg::Model
@@ -167,12 +167,12 @@ module OptargInternalFeature
 
   describe "Metadata" do
     it "preserves metadata" do
-      MetadataModel.definitions.options["-s"].metadata.as(MetadataModel::Metadata).data.should eq "string"
-      MetadataModel.definitions.options["-b"].metadata.as(MetadataModel::Metadata).data.should eq "bool"
-      MetadataModel.definitions.options["-a"].metadata.as(MetadataModel::Metadata).data.should eq "array"
-      MetadataModel.definitions.arguments["arg"].metadata.as(MetadataModel::Metadata).data.should eq "arg"
-      MetadataModel.definitions.handlers["--help"].metadata.as(MetadataModel::Metadata).data.should eq "handler"
-      MetadataModel.definitions.terminators["--"].metadata.as(MetadataModel::Metadata).data.should eq "terminator"
+      MetadataModel.__klass.definitions.options["-s"].metadata.as(MetadataModel::Metadata).data.should eq "string"
+      MetadataModel.__klass.definitions.options["-b"].metadata.as(MetadataModel::Metadata).data.should eq "bool"
+      MetadataModel.__klass.definitions.options["-a"].metadata.as(MetadataModel::Metadata).data.should eq "array"
+      MetadataModel.__klass.definitions.arguments["arg"].metadata.as(MetadataModel::Metadata).data.should eq "arg"
+      MetadataModel.__klass.definitions.handlers["--help"].metadata.as(MetadataModel::Metadata).data.should eq "handler"
+      MetadataModel.__klass.definitions.terminators["--"].metadata.as(MetadataModel::Metadata).data.should eq "terminator"
     end
   end
 end
diff --git a/src/lib/completion.cr b/src/lib/completion.cr
index 404e170..ec4a5c0 100644
--- a/src/lib/completion.cr
+++ b/src/lib/completion.cr
@@ -1,4 +1,5 @@
 module Optarg
+  # :nodoc:
   class Completion
     getter type : Symbol
     getter model : ModelClass
diff --git a/src/lib/completion_generators.cr b/src/lib/completion_generators.cr
index 3807b8f..377e9ac 100644
--- a/src/lib/completion_generators.cr
+++ b/src/lib/completion_generators.cr
@@ -1,2 +1,6 @@
+# :nodoc:
+module Optarg::CompletionGenerators
+end
+
 require "./completion_generators/base"
 require "./completion_generators/*"
diff --git a/src/lib/completion_generators/base.cr b/src/lib/completion_generators/base.cr
index f9fff82..ada345a 100644
--- a/src/lib/completion_generators/base.cr
+++ b/src/lib/completion_generators/base.cr
@@ -1,4 +1,4 @@
-class Optarg::CompletionGenerators
+module Optarg::CompletionGenerators
   abstract class Base
     include Completion::TextFormatter
 
diff --git a/src/lib/completion_generators/bash.cr b/src/lib/completion_generators/bash.cr
index 8bdb1eb..548ec3c 100644
--- a/src/lib/completion_generators/bash.cr
+++ b/src/lib/completion_generators/bash.cr
@@ -1,4 +1,4 @@
-class Optarg::CompletionGenerators
+module Optarg::CompletionGenerators
   class Bash < Base
   end
 end
diff --git a/src/lib/completion_generators/zsh.cr b/src/lib/completion_generators/zsh.cr
index 7f3b966..56d73ff 100644
--- a/src/lib/completion_generators/zsh.cr
+++ b/src/lib/completion_generators/zsh.cr
@@ -1,4 +1,4 @@
-class Optarg::CompletionGenerators
+module Optarg::CompletionGenerators
   class Zsh < Base
   end
 end
diff --git a/src/lib/definition_mixins.cr b/src/lib/definition_mixins.cr
index e8c5a1e..8f72a85 100644
--- a/src/lib/definition_mixins.cr
+++ b/src/lib/definition_mixins.cr
@@ -1 +1,5 @@
+# :nodoc:
+module Optarg::DefinitionMixins
+end
+
 require "./definition_mixins/*"
diff --git a/src/lib/definition_set.cr b/src/lib/definition_set.cr
index c8b9854..7e679f7 100644
--- a/src/lib/definition_set.cr
+++ b/src/lib/definition_set.cr
@@ -1,4 +1,5 @@
 module Optarg
+  # :nodoc:
   class DefinitionSet
     macro __set(types, list, array = nil)
       {%
diff --git a/src/lib/definitions.cr b/src/lib/definitions.cr
index 9648e4f..525ef27 100644
--- a/src/lib/definitions.cr
+++ b/src/lib/definitions.cr
@@ -1,2 +1,6 @@
+# :nodoc:
+module Optarg::Definitions
+end
+
 require "./definitions/base"
 require "./definitions/*"
diff --git a/src/lib/exceptions.cr b/src/lib/exceptions.cr
index 7c37da2..c97f9fa 100644
--- a/src/lib/exceptions.cr
+++ b/src/lib/exceptions.cr
@@ -1,18 +1,22 @@
 module Optarg
   class ParsingError < Exception
+    # :nodoc:
     getter parser : Parser
 
+    # :nodoc:
     def initialize(@parser, message)
       super message
     end
   end
 
+  # :nodoc:
   class UnknownOption < ParsingError
     def initialize(parser, name)
       super parser, "The #{name} option is unknown."
     end
   end
 
+  # :nodoc:
   class MissingValue < ParsingError
     getter option : DefinitionMixins::Option
 
@@ -21,6 +25,7 @@ module Optarg
     end
   end
 
+  # :nodoc:
   class UnsupportedConcatenation < ParsingError
     getter option : DefinitionMixins::Option
 
@@ -31,6 +36,7 @@ module Optarg
   end
 
   class ValidationError < ParsingError
+    # :nodoc:
     def initialize(parser, message)
       super parser, message
     end
diff --git a/src/lib/metadata.cr b/src/lib/metadata.cr
index 3a2b6a2..9630789 100644
--- a/src/lib/metadata.cr
+++ b/src/lib/metadata.cr
@@ -1,4 +1,5 @@
 module Optarg
+  # :nodoc:
   class Metadata
     @definition : Definitions::Base?
     def definition=(value)
diff --git a/src/lib/model.cr b/src/lib/model.cr
index 185a5c3..505f947 100644
--- a/src/lib/model.cr
+++ b/src/lib/model.cr
@@ -1,4 +1,5 @@
 module Optarg
+  # The base of model classes.
   abstract class Model
     macro inherited
       {% if @type.superclass == ::Optarg::Model %}
@@ -18,42 +19,23 @@ module Optarg
         %}
       {% end %}
 
-      {%
-        class_id = @type.name.underscore.split("::").join("__").id
-        last_concrete_id = "LastConcrete_#{class_id}".id
-      %}
-
-      {% if @type.abstract? %}
-        {%
-          last_concrete = superlast_concrete
-        %}
-      {% else %}
-        {%
-          last_concrete = @type
-        %}
-      {% end %}
-
-      {% if last_concrete %}
-        alias {{last_concrete_id}} = ::{{last_concrete}}
-      {% end %}
-
       @@__klass = ::Optarg::ModelClass.new(
         supermodel: {{ is_root ? nil : "::#{@type.superclass}.__klass".id }},
         name: {{@type.name.split("::")[-1].underscore}},
         abstract: {{@type.abstract?}}
       )
+      # :nodoc:
       def self.__klass; @@__klass; end
-      def self.klass; @@__klass; end
-
-      def self.__definitions; @@__klass.definitions; end
-      def self.definitions; @@__klass.definitions; end
 
       {% unless is_root %}
-        ::{{@type.superclass}}.__definitions.all.each do |kv|
-          __definitions << kv[1].subclassify(::{{@type}})
+        ::{{@type.superclass}}.__klass.definitions.all.each do |kv|
+          @@__klass.definitions << kv[1].subclassify(::{{@type}})
         end
       {% end %}
 
+      # A dedicated Optarg::Parser subclass for the model class.
+      #
+      # This class is automatically defined by the optarg library.
       {% if @type.abstract? %}
         abstract class Parser < ::{{superparser}}
           inherit_callback_group :validate, ::Proc(::{{@type}}, ::Nil)
@@ -62,7 +44,8 @@ module Optarg
         class Parser < ::{{superparser}}
           inherit_callback_group :validate, ::Proc(::{{@type}}, ::Nil)
 
-          def data
+          # Returns a target model instance.
+          def data : ::{{@type}}
             @data.as(::{{@type}})
           end
         end
@@ -71,6 +54,7 @@ module Optarg
           (@__parser.var ||= Parser.new(self)).as(Parser)
         end
 
+        # :nodoc:
         class DefinitionContext
           @definition : ::Optarg::Definitions::Base
 
@@ -86,74 +70,85 @@ module Optarg
           end
         end
 
+        # :nodoc:
         def self.__with_definition(df)
           yield DefinitionContext.new(df)
         end
       {% end %}
     end
 
+    # :nodoc:
+    def __klass; self.class.__klass; end
+
     @__parser = Util::Var(Parser).new
 
+    # :nodoc:
     getter __argv : Array(String)
 
+    # :nodoc:
     def initialize(@__argv)
     end
 
+    # :nodoc:
     def self.__parse(argv, *args)
       new(argv, *args).tap do |o|
         o.__parse
       end
     end
 
+    # Creates a new model instance and parses the *argv* arguments.
+    #
+    # Returns the created instance.
+    def self.parse(argv : Array(String), *args)
+      __parse(argv, *args)
+    end
+
+    # :nodoc:
     def __parse
       __parser.parse
     end
 
-    def self.klass; __klass; end
-    def self.parse(argv, *args); __parse(argv, *args); end
-
-    def parse; __parse; end
-    def parser; __parser; end
-
-    def __nameless_args; __parser.nameless_args; end
-    def nameless_args; __nameless_args; end
-
-    def __parsed_args; __parser.parsed_args; end
-    def parsed_args; __parsed_args; end
-
-    def __unparsed_args; __parser.unparsed_args; end
-    def unparsed_args; __unparsed_args; end
-
-    def __parsed_nodes; __parser.parsed_nodes; end
+    # Returns an array that contains nameless argument values.
+    def nameless_args; __parser.nameless_args; end
 
-    def __definitions; self.class.__definitions; end
+    # Returns an array that contains unparsed argument values.
+    def unparsed_args; __parser.unparsed_args; end
 
+    # Returns a value hash for String-type options and arguments.
     def [](klass : String.class)
       __parser.args[klass]
     end
 
+    # Returns a value hash for Bool-type options and arguments.
     def [](klass : Bool.class)
       __parser.args[klass]
     end
 
+    # Returns a value hash for Array(String)-type options and arguments.
     def [](klass : Array(String).class)
       __parser.args[klass]
     end
 
+    # Returns an argument value at the *index*.
     def [](index : Int32)
       __parser.parsed_args[index]
     end
 
+    # Returns an argument value at the *index*.
+    #
+    # Returns nil if the *index* is out of range.
     def []?(index : Int32)
       __parser.parsed_args[index]?
     end
 
+    # Iterates argument values.
     def each
       __parser.parsed_args.each do |i|
         yield i
       end
     end
 
+    # :nodoc:
     def self.__with_self(*args)
       with self yield *args
     end
diff --git a/src/lib/model/dsl/arg.cr b/src/lib/model/dsl/arg.cr
index 477b827..15864ab 100644
--- a/src/lib/model/dsl/arg.cr
+++ b/src/lib/model/dsl/arg.cr
@@ -1,9 +1,10 @@
 module Optarg
   class Model
+    # Defines a String argument model item.
     macro arg(names, metadata = nil, stop = nil, default = nil, required = nil, any_of = nil, complete = nil, _mixin = nil, &block)
-      define_static_value :argument, :nilable, ::Optarg::Definitions::StringArgument, {{names}}, nil, {{_mixin}} do |klass|
+      __define_static_value :argument, :nilable, ::Optarg::Definitions::StringArgument, {{names}}, nil, {{_mixin}} do |klass|
         arg = klass.new({{names}}, metadata: {{metadata}}, stop: {{stop}}, required: {{required}}, default: {{default}}, any_of: {{any_of}}, complete: {{complete}})
-        __definitions << arg
+        @@__klass.definitions << arg
         {% if block %}
           __with_definition(option) {{block}}
         {% end %}
diff --git a/src/lib/model/dsl/arg_array.cr b/src/lib/model/dsl/arg_array.cr
index e3fcfff..b097658 100644
--- a/src/lib/model/dsl/arg_array.cr
+++ b/src/lib/model/dsl/arg_array.cr
@@ -1,9 +1,10 @@
 module Optarg
   class Model
+    # Defines an Array(String) argument model item.
     macro arg_array(names, metadata = nil, default = nil, min = nil, any_item_of = nil, complete = nil, _mixin = nil, &block)
-      define_static_value :argument, :nilable, ::Optarg::Definitions::StringArrayArgument, {{names}}, nil, {{_mixin}} do |klass|
+      __define_static_value :argument, :nilable, ::Optarg::Definitions::StringArrayArgument, {{names}}, nil, {{_mixin}} do |klass|
         option = klass.new({{names}}, metadata: {{metadata}}, default: {{default}}, min: {{min}}, any_item_of: {{any_item_of}}, complete: {{complete}})
-        __definitions << option
+        @@__klass.definitions << option
         {% if block %}
           __with_definition(option) {{block}}
         {% end %}
diff --git a/src/lib/model/dsl/array.cr b/src/lib/model/dsl/array.cr
index cbb2b68..d44ad64 100644
--- a/src/lib/model/dsl/array.cr
+++ b/src/lib/model/dsl/array.cr
@@ -1,9 +1,10 @@
 module Optarg
   class Model
+    # Defines an Array(String) option model item.
     macro array(names, metadata = nil, default = nil, min = nil, any_item_of = nil, complete = nil, _mixin = nil, &block)
-      define_static_value :option, :nilable, ::Optarg::Definitions::StringArrayOption, {{names}}, nil, {{_mixin}} do |klass|
+      __define_static_value :option, :nilable, ::Optarg::Definitions::StringArrayOption, {{names}}, nil, {{_mixin}} do |klass|
         option = klass.new({{names}}, metadata: {{metadata}}, default: {{default}}, min: {{min}}, any_item_of: {{any_item_of}}, complete: {{complete}})
-        __definitions << option
+        @@__klass.definitions << option
         {% if block %}
           __with_definition(option) {{block}}
         {% end %}
diff --git a/src/lib/model/dsl/bool.cr b/src/lib/model/dsl/bool.cr
index 6730939..632d8a9 100644
--- a/src/lib/model/dsl/bool.cr
+++ b/src/lib/model/dsl/bool.cr
@@ -1,12 +1,13 @@
 module Optarg
   class Model
+    # Defines a Bool option model item.
     macro bool(names, metadata = nil, stop = nil, default = nil, not = nil, _mixin = nil, &block)
-      define_static_value :option, :predicate, ::Optarg::Definitions::BoolOption, {{names}}, nil, {{_mixin}} do  |klass|
+      __define_static_value :option, :predicate, ::Optarg::Definitions::BoolOption, {{names}}, nil, {{_mixin}} do  |klass|
         option = klass.new({{names}}, metadata: {{metadata}}, stop: {{stop}}, default: {{default}})
-        __definitions << option
+        @@__klass.definitions << option
         {% if not %}
           not = ::Optarg::Definitions::NotOption.new({{not}}, option, metadata: nil, stop: {{stop}})
-          __definitions << not
+          @@__klass.definitions << not
         {% end %}
         {% if block %}
           __with_definition(option) {{block}}
diff --git a/src/lib/model/dsl/handler.cr b/src/lib/model/dsl/handler.cr
index 6e9e854..360d29d 100644
--- a/src/lib/model/dsl/handler.cr
+++ b/src/lib/model/dsl/handler.cr
@@ -1,9 +1,10 @@
 module Optarg
   class Model
+    # Defines a handler model item.
     macro on(names, metadata = nil, stop = nil, &block)
-      define_static_handler nil, {{names}} {{block}}
-      %handler = create_static_handler({{names}}, metadata: {{metadata}}, stop: {{stop}})
-      __definitions << %handler
+      __define_static_handler nil, {{names}} {{block}}
+      %handler = __create_static_handler({{names}}, metadata: {{metadata}}, stop: {{stop}})
+      @@__klass.definitions << %handler
     end
   end
 end
diff --git a/src/lib/model/dsl/string.cr b/src/lib/model/dsl/string.cr
index 79edd63..ccc89b7 100644
--- a/src/lib/model/dsl/string.cr
+++ b/src/lib/model/dsl/string.cr
@@ -1,9 +1,10 @@
 module Optarg
   class Model
+    # Defines a String option model item.
     macro string(names, metadata = nil, stop = nil, default = nil, required = nil, any_of = nil, complete = nil, _mixin = nil, &block)
-      define_static_value :option, :nilable, ::Optarg::Definitions::StringOption, {{names}}, nil, {{_mixin}} do |klass|
+      __define_static_value :option, :nilable, ::Optarg::Definitions::StringOption, {{names}}, nil, {{_mixin}} do |klass|
         option = klass.new({{names}}, metadata: {{metadata}}, stop: {{stop}}, default: {{default}}, required: {{required}}, any_of: {{any_of}}, complete: {{complete}})
-        __definitions << option
+        @@__klass.definitions << option
         {% if block %}
           __with_definition(option) {{block}}
         {% end %}
diff --git a/src/lib/model/dsl/terminator.cr b/src/lib/model/dsl/terminator.cr
index ed3967f..e1f5cc8 100644
--- a/src/lib/model/dsl/terminator.cr
+++ b/src/lib/model/dsl/terminator.cr
@@ -1,8 +1,9 @@
 module Optarg
   class Model
+    # Defines a terminator model item.
     macro terminator(names, metadata = nil)
       %term = ::Optarg::Definitions::Terminator.new({{names}}, metadata: {{metadata}})
-      __definitions << %term
+      @@__klass.definitions << %term
     end
   end
 end
diff --git a/src/lib/model/macros/handler.cr b/src/lib/model/macros/handler.cr
index 22d2b0d..89ee043 100644
--- a/src/lib/model/macros/handler.cr
+++ b/src/lib/model/macros/handler.cr
@@ -1,6 +1,7 @@
 module Optarg
   class Model
-    macro define_static_handler(type, names, &block)
+    # :nodoc:
+    macro __define_static_handler(type, names, &block)
       {%
         names = [names] unless names.class_name == "ArrayLiteral"
         method_names = names.map{|i| i.split("=")[0].gsub(/^-*/, "").gsub(/-/, "_")}
@@ -8,10 +9,12 @@ module Optarg
         df_class = "Handler__#{name}".id
       %}
 
+      # :nodoc:
       def __call_handler_for__{{name}}
         {{block.body}}
       end
 
+      # :nodoc:
       class {{df_class}} < ::Optarg::Definitions::Handler
         def visit(parser)
           if data = parser.data.as?(::{{@type}})
@@ -26,7 +29,8 @@ module Optarg
       end
     end
 
-    macro create_static_handler(names, metadata, stop)
+    # :nodoc:
+    macro __create_static_handler(names, metadata, stop)
       {%
         names = [names] unless names.class_name == "ArrayLiteral"
         method_names = names.map{|i| i.split("=")[0].gsub(/^-*/, "").gsub(/-/, "_")}
diff --git a/src/lib/model/macros/value.cr b/src/lib/model/macros/value.cr
index 79a951b..eba432c 100644
--- a/src/lib/model/macros/value.cr
+++ b/src/lib/model/macros/value.cr
@@ -1,6 +1,7 @@
 module Optarg
   class Model
-    macro define_static_value(kind, access_type, metaclass, names, value_key, _mixin, &block)
+    # :nodoc:
+    macro __define_static_value(kind, access_type, metaclass, names, value_key, _mixin, &block)
       {%
         kind = kind.id
         metaclass = metaclass.resolve
@@ -16,11 +17,13 @@ module Optarg
 
       {% if kind == :argument %}
         {%
+          value_name = key.upcase
           container_method = "self".id
           df_getter = "#{method_names[0]}_arg".id
         %}
       {% else %}
         {%
+          value_name = key
           container_method = "self".id
           df_getter = "#{method_names[0]}_option".id
         %}
@@ -29,18 +32,29 @@ module Optarg
       {% for method_name, index in method_names %}
         {% if access_type == :predicate %}
           {% unless model_reserved.includes?("#{method_name}?".id) %}
+            # Returns the {{value_name}} {{kind.id}} value.
+            #
+            # This method is automatically defined by the optarg library.
             def {{method_name}}?
               !!{{container_method}}[::{{metaclass}}::Typed::Type][{{value_key}}]?
             end
           {% end %}
         {% elsif access_type == :nilable %}
           {% unless model_reserved.includes?(method_name) %}
+            # Returns the {{value_name}} {{kind.id}} value.
+            #
+            # This method is automatically defined by the optarg library.
             def {{method_name}}
               {{container_method}}[::{{metaclass}}::Typed::Type][{{value_key}}]
             end
           {% end %}
 
           {% unless model_reserved.includes?("#{method_name}?".id) %}
+            # Returns the {{value_name}} {{kind.id}} value.
+            #
+            # Returns nil, if the value is undefined.
+            #
+            # This method is automatically defined by the optarg library.
             def {{method_name}}?
               {{container_method}}[::{{metaclass}}::Typed::Type][{{value_key}}]?
             end
diff --git a/src/lib/model_class.cr b/src/lib/model_class.cr
index 6cb9a13..7d09cf9 100644
--- a/src/lib/model_class.cr
+++ b/src/lib/model_class.cr
@@ -1,4 +1,5 @@
 module Optarg
+  # :nodoc:
   class ModelClass
     property name : String
     getter? abstract : Bool
diff --git a/src/lib/parser.cr b/src/lib/parser.cr
index 7f497db..f62dc35 100644
--- a/src/lib/parser.cr
+++ b/src/lib/parser.cr
@@ -3,28 +3,46 @@ module Optarg
     ::Callback.enable
     define_callback_group :validate, Proc(Model, Nil)
 
+    # :nodoc:
     alias Node = NamedTuple(args: Array(String), definitions: Array(Definitions::Base))
 
+    # Returns a target model instance.
     getter data : Model
 
+    # :nodoc:
     getter parsed_nodes = [] of Node
-    getter! args : ValueContainer
+
+    # :nodoc:
     getter nameless_args = %w()
+
+    # :nodoc:
     getter parsed_args = %w()
+
+    # :nodoc:
     getter unparsed_args = %w()
 
     @argument_index = 0
+    # :nodoc:
     getter index = 0
 
+    # :nodoc:
     def initialize(data)
       @data = data
       @args = ValueContainer.new(self)
     end
 
+    @args : ValueContainer?
+    # :nodoc:
+    def args
+      @args.not_nil!
+    end
+
+    # :nodoc:
     def input_args
       data.__argv
     end
 
+    # :nodoc:
     def self.new_node(args = %w(), *definitions)
       node = {args: args, definitions: [] of Definitions::Base}
       definitions.each do |df|
@@ -34,10 +52,12 @@ module Optarg
     end
 
     @definitions : DefinitionSet?
+    # :nodoc:
     def definitions
-      @definitions ||= data.__definitions
+      @definitions ||= data.__klass.definitions
     end
 
+    # :nodoc:
     def stopped?
       return false if parsed_nodes.size == 0
       return parsed_nodes.last[:definitions].any?{|i| i.stops? || i.terminates?}
@@ -49,6 +69,7 @@ module Optarg
       end
     end
 
+    # :nodoc:
     def parse
       definitions.all.each do |kv|
         kv[1].initialize_before_parse(self)
@@ -61,10 +82,12 @@ module Optarg
       end
     end
 
+    # :nodoc:
     def eol?
       @index == input_args.size
     end
 
+    # :nodoc:
     def resume
       until eol? || stopped?
         visit
@@ -74,6 +97,7 @@ module Optarg
       @index = input_args.size
     end
 
+    # :nodoc:
     def visit
       arg = self[0]
       if visit_terminator
@@ -86,6 +110,7 @@ module Optarg
       end
     end
 
+    # :nodoc:
     def visit_terminator
       name = self[0]
       if node = find_with_def(definitions.terminators, self[0]){|df| df.visit(self)}
@@ -94,6 +119,7 @@ module Optarg
       end
     end
 
+    # :nodoc:
     def find_with_def(dfs, name)
       dfs.each do |kv|
         next unless kv[1].matches?(name)
@@ -103,6 +129,7 @@ module Optarg
       nil
     end
 
+    # :nodoc:
     def visit_concatenated_options
       names = self[0][1..-1].split("").map{|i| "-#{i}"}
       node = Parser.new_node([self[0]])
@@ -117,6 +144,7 @@ module Optarg
       @index += 1
     end
 
+    # :nodoc:
     def visit_option
       name = self[0]
       if node = find_with_def(definitions.options, name){|df| df.visit(self)}
@@ -127,6 +155,7 @@ module Optarg
       end
     end
 
+    # :nodoc:
     def visit_argument
       while @argument_index < definitions.arguments.size
         df = definitions.argument_list[@argument_index]
@@ -146,18 +175,22 @@ module Optarg
       @index += 1
     end
 
+    # :nodoc:
     def [](*args)
       input_args[@index..-1][*args]
     end
 
+    # :nodoc:
     def left
       input_args.size - @index
     end
 
+    # Creates and raises a new `ValidationError` with the *message*.
     def invalidate!(message : String)
       invalidate! ValidationError.new(self, message)
     end
 
+    # :nodoc:
     def invalidate!(ex : ValidationError)
       raise ex
     end
diff --git a/src/lib/util.cr b/src/lib/util.cr
index 2551595..8d719d8 100644
--- a/src/lib/util.cr
+++ b/src/lib/util.cr
@@ -1 +1,5 @@
+# :nodoc:
+module Optarg::Util
+end
+
 require "./util/*"
diff --git a/src/lib/validation_context.cr b/src/lib/validation_context.cr
index e1fff56..71b1aba 100644
--- a/src/lib/validation_context.cr
+++ b/src/lib/validation_context.cr
@@ -1,4 +1,5 @@
 module Optarg
+  # :nodoc:
   class ValidationContext
     @parser : Parser
     @definition : Definitions::Base
diff --git a/src/lib/value.cr b/src/lib/value.cr
index e3230af..7d82633 100644
--- a/src/lib/value.cr
+++ b/src/lib/value.cr
@@ -1,4 +1,5 @@
 module Optarg
+  # :nodoc:
   abstract class Value(T)
     include ::Comparable(Value(T))
 
diff --git a/src/lib/value_container.cr b/src/lib/value_container.cr
index af33755..44723bc 100644
--- a/src/lib/value_container.cr
+++ b/src/lib/value_container.cr
@@ -1,4 +1,5 @@
 module Optarg
+  # :nodoc:
   class ValueContainer
     getter strings : ValueTypes::String::ValueHash
     getter bools : ValueTypes::Bool::ValueHash
diff --git a/src/lib/value_hash.cr b/src/lib/value_hash.cr
index 0c24792..de7e37c 100644
--- a/src/lib/value_hash.cr
+++ b/src/lib/value_hash.cr
@@ -1,4 +1,5 @@
 module Optarg
+  # :nodoc:
   abstract class ValueHash(V) < Hash(String, V)
     @fallbacked = {} of String => Bool
     @parser : Parser
diff --git a/src/lib/value_metadata.cr b/src/lib/value_metadata.cr
index 903861a..a210706 100644
--- a/src/lib/value_metadata.cr
+++ b/src/lib/value_metadata.cr
@@ -1,4 +1,5 @@
 module Optarg
+  # :nodoc:
   class ValueMetadata(T)
     @value : Value(T)?
 
diff --git a/src/lib/value_types.cr b/src/lib/value_types.cr
index f52a2d2..739e8bf 100644
--- a/src/lib/value_types.cr
+++ b/src/lib/value_types.cr
@@ -1 +1,5 @@
+# :nodoc:
+module Optarg::ValueTypes
+end
+
 require "./value_types/*"
diff --git a/src/lib/value_types/base.cr b/src/lib/value_types/base.cr
index c4481a7..fd33a81 100644
--- a/src/lib/value_types/base.cr
+++ b/src/lib/value_types/base.cr
@@ -53,6 +53,7 @@ module Optarg::ValueTypes
                 Error.new(parser, df, self, message)
               end
 
+              # :nodoc:
               class Error < ::Optarg::ValidationError
                 getter definition : ::{{type}}
                 getter validation : ::\{{@type}}
diff --git a/src/lib/value_validation.cr b/src/lib/value_validation.cr
index 1002d9f..a172903 100644
--- a/src/lib/value_validation.cr
+++ b/src/lib/value_validation.cr
@@ -1,4 +1,5 @@
 module Optarg
+  # :nodoc:
   abstract class ValueValidation
   end
 end