diff --git a/lib/redmine/plugin.rb b/lib/redmine/plugin.rb
index 203c50881..642755761 100644
--- a/lib/redmine/plugin.rb
+++ b/lib/redmine/plugin.rb
@@ -16,8 +16,14 @@
 # Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301, USA.
 
 module Redmine
-
+  # Exception on specified plugin was not found.
+  #
+  # @since 0.8.0
   class PluginNotFound < StandardError; end
+
+  # Exception on required incompatible plugin with redmine.
+  #
+  # @since 0.8.0
   class PluginRequirementError < StandardError; end
 
   # Base class for Redmine plugins.
@@ -37,15 +43,22 @@ module Redmine
   # It must be a hash with the following keys:
   # * <tt>:default</tt>: default value for the plugin settings
   # * <tt>:partial</tt>: path of the configuration partial view, relative to the plugin <tt>app/views</tt> directory
-  # Example:
+  # @example
   #   settings :default => {'foo'=>'bar'}, :partial => 'settings/settings'
   # In this example, the settings partial will be found here in the plugin directory: <tt>app/views/settings/_settings.rhtml</tt>.
   #
   # When rendered, the plugin settings value is available as the local variable +settings+
+  #
+  # @since 0.6.0
+  # @see http://www.redmine.org/projects/redmine/wiki/Plugin_Tutorial
   class Plugin
+    # @attr [String] self.directory redmine plugin directory.
+    # @since 2.0.0
     cattr_accessor :directory
     self.directory = File.join(Rails.root, 'plugins')
 
+    # @attr [String] self.public_directory Redmine pulugin's public directory.
+    # @since 1.4.0
     cattr_accessor :public_directory
     self.public_directory = File.join(Rails.root, 'public', 'plugin_assets')
 
@@ -53,9 +66,11 @@ module Redmine
     @used_partials = {}
 
     class << self
+      # @since 0.6.0
       attr_reader :registered_plugins
       private :new
 
+      # @since 0.6.0
       def def_field(*names)
         class_eval do
           names.each do |name|
@@ -67,9 +82,23 @@ module Redmine
       end
     end
     def_field :name, :description, :url, :author, :author_url, :version, :settings, :directory
+    # @since 0.8.0
     attr_reader :id
 
     # Plugin constructor
+    # @param [String, Symbol] id plugin id.
+    # @yield Evaluates block with no block parameter. In block, self is new Redmine::Plugin object with specified id. Redmine::Plugin instance methods can call without receiver to new plugin object.
+    # @example
+    #   Redmine::Plugin.register :example do
+    #     name 'Example plugin'
+    #     author 'John Smith'
+    #     description 'This is an example plugin for Redmine'
+    #     version '0.0.1'
+    #     requires_redmine version_or_higher: '3.0.0'
+    #   end
+    #
+    # @since 0.6.0
+    # @see Redmine::Plugin#requires_redmine
     def self.register(id, &block)
       p = new(id)
       p.instance_eval(&block)
@@ -114,35 +143,49 @@ module Redmine
     end
 
     # Returns an array of all registered plugins
+    #
+    # @return [[Redmine::Plugin]] an array of plugins
+    # @since 0.8.0
     def self.all
       registered_plugins.values.sort
     end
 
     # Finds a plugin by its id
     # Returns a PluginNotFound exception if the plugin doesn't exist
+    #
+    # @param [String, Symbol] id name of the plugin
+    # @return [Redmine::Plugin] Redmine plugin
+    # @since 0.8.0
     def self.find(id)
       registered_plugins[id.to_sym] || raise(PluginNotFound)
     end
 
     # Clears the registered plugins hash
     # It doesn't unload installed plugins
+    #
+    # @since 0.8.0
     def self.clear
       @registered_plugins = {}
     end
 
     # Removes a plugin from the registered plugins
     # It doesn't unload the plugin
+    #
+    # @param [String, Symbol] id name of the plugin
+    # @since 2.6.0
     def self.unregister(id)
       @registered_plugins.delete(id)
     end
 
     # Checks if a plugin is installed
     #
-    # @param [String] id name of the plugin
+    # @param [String, Symbol] id name of the plugin
+    # @since 1.0.3
     def self.installed?(id)
       registered_plugins[id.to_sym].present?
     end
 
+    # @since 2.0.0
     def self.load
       Dir.glob(File.join(self.directory, '*')).sort.each do |directory|
         if File.directory?(directory)
@@ -159,22 +202,29 @@ module Redmine
       end
     end
 
+    # @since 0.8.0
     def initialize(id)
       @id = id.to_sym
     end
 
+    # @since 2.0.0
     def public_directory
       File.join(self.class.public_directory, id.to_s)
     end
 
+    # @since 2.3.0
     def to_param
       id
     end
 
+    # plugin assets directory
+    #
+    # @since 2.0.0
     def assets_directory
       File.join(directory, 'assets')
     end
 
+    # @since 0.8.0
     def <=>(plugin)
       self.id.to_s <=> plugin.id.to_s
     end
@@ -182,7 +232,7 @@ module Redmine
     # Sets a requirement on Redmine version
     # Raises a PluginRequirementError exception if the requirement is not met
     #
-    # Examples
+    # @example
     #   # Requires Redmine 0.7.3 or higher
     #   requires_redmine :version_or_higher => '0.7.3'
     #   requires_redmine '0.7.3'
@@ -198,6 +248,8 @@ module Redmine
     #   # Requires a Redmine version within a range
     #   requires_redmine :version => '0.7.3'..'0.9.1'     # >= 0.7.3 and <= 0.9.1
     #   requires_redmine :version => '0.7'..'0.9'         # >= 0.7.x and <= 0.9.x
+    #
+    # @since 0.8.0
     def requires_redmine(arg)
       arg = { :version_or_higher => arg } unless arg.is_a?(Hash)
       arg.assert_valid_keys(:version, :version_or_higher)
@@ -228,6 +280,7 @@ module Redmine
       true
     end
 
+    # @since 2.2.0
     def compare_versions(requirement, current)
       requirement = requirement.split('.').collect(&:to_i)
       requirement <=> current.slice(0, requirement.size)
@@ -237,7 +290,7 @@ module Redmine
     # Sets a requirement on a Redmine plugin version
     # Raises a PluginRequirementError exception if the requirement is not met
     #
-    # Examples
+    # @example
     #   # Requires a plugin named :foo version 0.7.3 or higher
     #   requires_redmine_plugin :foo, :version_or_higher => '0.7.3'
     #   requires_redmine_plugin :foo, '0.7.3'
@@ -245,6 +298,8 @@ module Redmine
     #   # Requires a specific version of a Redmine plugin
     #   requires_redmine_plugin :foo, :version => '0.7.3'              # 0.7.3 only
     #   requires_redmine_plugin :foo, :version => ['0.7.3', '0.8.0']   # 0.7.3 or 0.8.0
+    #
+    # @since 0.9.0
     def requires_redmine_plugin(plugin_name, arg)
       arg = { :version_or_higher => arg } unless arg.is_a?(Hash)
       arg.assert_valid_keys(:version, :version_or_higher)
@@ -276,12 +331,16 @@ module Redmine
     #
     # +name+ parameter can be: :top_menu, :account_menu, :application_menu or :project_menu
     #
+    # @since 0.6.0
     def menu(menu, item, url, options={})
       Redmine::MenuManager.map(menu).push(item, url, options)
     end
+    # @since 0.8.0
     alias :add_menu_item :menu
 
     # Removes +item+ from the given +menu+.
+    #
+    # @since 0.8.0
     def delete_menu_item(menu, item)
       Redmine::MenuManager.map(menu).delete(item)
     end
@@ -297,7 +356,7 @@ module Redmine
     # * :require => can be set to one of the following values to restrict users the permission can be given to: :loggedin, :member
     # * :read => set it to true so that the permission is still granted on closed projects
     #
-    # Examples
+    # @example
     #   # A permission that is implicitly given to any user
     #   # This permission won't appear on the Roles & Permissions setup screen
     #   permission :say_hello, { :example => :say_hello }, :public => true, :read => true
@@ -310,6 +369,8 @@ module Redmine
     #
     #   # A permission that can be given to project members only
     #   permission :say_hello, { :example => :say_hello }, :require => :member
+    #
+    # @since 0.6.0
     def permission(name, actions, options = {})
       if @project_module
         Redmine::AccessControl.map {|map| map.project_module(@project_module) {|map|map.permission(name, actions, options)}}
@@ -325,6 +386,8 @@ module Redmine
     #     permission :view_contacts, { :contacts => [:list, :show] }, :public => true
     #     permission :destroy_contacts, { :contacts => :destroy }
     #   end
+    #
+    # @since 0.6.0
     def project_module(name, &block)
       @project_module = name
       self.instance_eval(&block)
@@ -339,7 +402,7 @@ module Redmine
     #
     # A model can provide several activity event types.
     #
-    # Examples:
+    # @example
     #   register :news
     #   register :scrums, :class_name => 'Meeting'
     #   register :issues, :class_name => ['Issue', 'Journal']
@@ -353,6 +416,8 @@ module Redmine
     #   Meeting.find_events('scrums', User.current, 5.days.ago, Date.today, :project => foo) # events for project foo only
     #
     # Note that :view_scrums permission is required to view these events in the activity view.
+    #
+    # @since 0.8.0
     def activity_provider(*args)
       Redmine::Activity.register(*args)
     end
@@ -367,18 +432,22 @@ module Redmine
     # * +options+ - a Hash of options (optional)
     #   * :label - label for the formatter displayed in application settings
     #
-    # Examples:
+    # @example
     #   wiki_format_provider(:custom_formatter, CustomFormatter, :label => "My custom formatter") 
     #
+    # @since 0.8.0
     def wiki_format_provider(name, *args)
       Redmine::WikiFormatting.register(name, *args)
     end
 
     # Returns +true+ if the plugin can be configured.
+    #
+    # @since 0.6.0
     def configurable?
       settings && settings.is_a?(Hash) && !settings[:partial].blank?
     end
 
+    # @since 2.0.0
     def mirror_assets
       source = assets_directory
       destination = public_directory
@@ -421,6 +490,8 @@ module Redmine
     end
 
     # Mirrors assets from one or all plugins to public/plugin_assets
+    #
+    # @since 2.0.0
     def self.mirror_assets(name=nil)
       if name.present?
         find(name).mirror_assets
@@ -432,23 +503,31 @@ module Redmine
     end
 
     # The directory containing this plugin's migrations (<tt>plugin/db/migrate</tt>)
+    #
+    # @since 2.0.0
     def migration_directory
       File.join(directory, 'db', 'migrate')
     end
 
     # Returns the version number of the latest migration for this plugin. Returns
     # nil if this plugin has no migrations.
+    #
+    # @since 2.0.0
     def latest_migration
       migrations.last
     end
 
     # Returns the version numbers of all migrations for this plugin.
+    #
+    # @since 2.0.0
     def migrations
       migrations = Dir[migration_directory+"/*.rb"]
       migrations.map { |p| File.basename(p).match(/0*(\d+)\_/)[1].to_i }.sort
     end
 
     # Migrate this plugin to the given version
+    #
+    # @since 2.0.0
     def migrate(version = nil)
       puts "Migrating #{id} (#{name})..."
       Redmine::Plugin::Migrator.migrate_plugin(self, version)
@@ -460,6 +539,7 @@ module Redmine
     #   Plugin.migrate('sample_plugin')
     #   Plugin.migrate('sample_plugin', 1)
     #
+    # @since 2.0.0
     def self.migrate(name=nil, version=nil)
       if name.present?
         find(name).migrate(version)
@@ -470,18 +550,24 @@ module Redmine
       end
     end
 
+    # @since 2.0.0
     class Migrator < ActiveRecord::Migrator
       # We need to be able to set the 'current' plugin being migrated.
+      #
+      # @since 2.0.0
       cattr_accessor :current_plugin
 
       class << self
         # Runs the migrations from a plugin, up (or down) to the version given
+        #
+        # @since 2.0.0
         def migrate_plugin(plugin, version)
           self.current_plugin = plugin
           return if current_version(plugin) == version
           migrate(plugin.migration_directory, version)
         end
 
+        # @since 2.0.0
         def current_version(plugin=current_plugin)
           # Delete migrations that don't match .. to_i will work because the number comes first
           sm_table = ::ActiveRecord::SchemaMigration.table_name
@@ -491,6 +577,7 @@ module Redmine
         end
       end
 
+      # @since 2.0.0
       def migrated
         sm_table = ::ActiveRecord::SchemaMigration.table_name
         ::ActiveRecord::Base.connection.select_values(
@@ -498,6 +585,7 @@ module Redmine
         ).delete_if{ |v| v.match(/-#{current_plugin.id}$/) == nil }.map(&:to_i).sort
       end
 
+      # @since 2.0.0
       def record_version_state_after_migrating(version)
         super(version.to_s + "-" + current_plugin.id.to_s)
       end