18 files changed, 167 insertions, 106 deletions
diff --git a/guides/source/2_3_release_notes.md b/guides/source/2_3_release_notes.md
index 6976848e95..3f5a3c7ade 100644
--- a/guides/source/2_3_release_notes.md
+++ b/guides/source/2_3_release_notes.md
@@ -10,7 +10,7 @@ Rails 2.3 delivers a variety of new and improved features, including pervasive R
 Application Architecture
 ------------------------
 
-There are two major changes in the architecture of Rails applications: complete integration of the [Rack](http://rack.github.io/) modular web server interface, and renewed support for Rails Engines.
+There are two major changes in the architecture of Rails applications: complete integration of the [Rack](https://rack.github.io/) modular web server interface, and renewed support for Rails Engines.
 
 ### Rack Integration
 
diff --git a/guides/source/5_0_release_notes.md b/guides/source/5_0_release_notes.md
index 5f4be07351..6d53e1c2b4 100644
--- a/guides/source/5_0_release_notes.md
+++ b/guides/source/5_0_release_notes.md
@@ -55,7 +55,7 @@ information.
 ### API Applications
 
 Rails can now be used to create slimmed down API only applications.
-This is useful for creating and serving APIs similar to [Twitter](https://dev.twitter.com) or [GitHub](http://developer.github.com) API, 
+This is useful for creating and serving APIs similar to [Twitter](https://dev.twitter.com) or [GitHub](https://developer.github.com) API, 
 that can be used to serve public facing, as well as, for custom applications.
 
 You can generate a new api Rails app using:
@@ -74,11 +74,11 @@ This will do three main things:
   Controller modules that provide functionalities primarily used by browser
   applications.
 - Configure the generators to skip generating views, helpers and assets when
-  you generate a new resource. 
+  you generate a new resource.
 
-The application provides a base for APIs, 
+The application provides a base for APIs,
 that can then be [configured to pull in functionality](api_app.html) as suitable for the application's needs.  
- 
+
 See the [Using Rails for API-only Applications](api_app.html) guide for more
 information.
 
diff --git a/guides/source/active_record_callbacks.md b/guides/source/active_record_callbacks.md
index fc4f773e3c..53417f012e 100644
--- a/guides/source/active_record_callbacks.md
+++ b/guides/source/active_record_callbacks.md
@@ -429,7 +429,7 @@ end
 
 WARNING. The `after_commit` and `after_rollback` callbacks are called for all models created, updated, or destroyed within a transaction block. However, if an exception is raised within one of these callbacks, the exception will bubble up and any remaining `after_commit` or `after_rollback` methods will _not_ be executed. As such, if your callback code could raise an exception, you'll need to rescue it and handle it within the callback in order to allow other callbacks to run.
 
-WARNING. Using `after_create_commit` and `after_update_commit` both in the same model will override the callback which was registered first amongst them.
+WARNING. Using both `after_create_commit` and `after_update_commit` in the same model will only allow the last callback defined to take effect, and will override all others.
 
 ```ruby
 class User < ApplicationRecord
diff --git a/guides/source/active_record_validations.md b/guides/source/active_record_validations.md
index a086363cf1..e9157f3db1 100644
--- a/guides/source/active_record_validations.md
+++ b/guides/source/active_record_validations.md
@@ -892,7 +892,7 @@ Conditional Validation
 
 Sometimes it will make sense to validate an object only when a given predicate
 is satisfied. You can do that by using the `:if` and `:unless` options, which
-can take a symbol, a string, a `Proc` or an `Array`. You may use the `:if`
+can take a symbol, a `Proc` or an `Array`. You may use the `:if`
 option when you want to specify when the validation **should** happen. If you
 want to specify when the validation **should not** happen, then you may use the
 `:unless` option.
diff --git a/guides/source/api_app.md b/guides/source/api_app.md
index 64200ec242..5ec79de8a0 100644
--- a/guides/source/api_app.md
+++ b/guides/source/api_app.md
@@ -18,7 +18,7 @@ What is an API Application?
 
 Traditionally, when people said that they used Rails as an "API", they meant
 providing a programmatically accessible API alongside their web application.
-For example, GitHub provides [an API](http://developer.github.com) that you
+For example, GitHub provides [an API](https://developer.github.com) that you
 can use from your own custom clients.
 
 With the advent of client-side frameworks, more developers are using Rails to
@@ -94,7 +94,7 @@ Handled at the Action Pack layer:
   means not having to spend time thinking about how to model your API in terms
   of HTTP.
 - URL Generation: The flip side of routing is URL generation. A good API based
-  on HTTP includes URLs (see [the GitHub Gist API](http://developer.github.com/v3/gists/)
+  on HTTP includes URLs (see [the GitHub Gist API](https://developer.github.com/v3/gists/)
   for an example).
 - Header and Redirection Responses: `head :no_content` and
   `redirect_to user_url(current_user)` come in handy. Sure, you could manually
diff --git a/guides/source/asset_pipeline.md b/guides/source/asset_pipeline.md
index a02eebf263..f148cef24f 100644
--- a/guides/source/asset_pipeline.md
+++ b/guides/source/asset_pipeline.md
@@ -283,10 +283,10 @@ You can view the search path by inspecting
 `Rails.application.config.assets.paths` in the Rails console.
 
 Besides the standard `assets/*` paths, additional (fully qualified) paths can be
-added to the pipeline in `config/application.rb`. For example:
+added to the pipeline in `config/initializers/assets.rb`. For example:
 
 ```ruby
-config.assets.paths << Rails.root.join("lib", "videoplayer", "flash")
+Rails.application.config.assets.paths << Rails.root.join("lib", "videoplayer", "flash")
 ```
 
 Paths are traversed in the order they occur in the search path. By default,
@@ -1069,7 +1069,7 @@ Customizing the Pipeline
 ### CSS Compression
 
 One of the options for compressing CSS is YUI. The [YUI CSS
-compressor](http://yui.github.io/yuicompressor/css.html) provides
+compressor](https://yui.github.io/yuicompressor/css.html) provides
 minification.
 
 The following line enables YUI compression, and requires the `yui-compressor`
diff --git a/guides/source/command_line.md b/guides/source/command_line.md
index 9fddbf76b6..2cd8e02a77 100644
--- a/guides/source/command_line.md
+++ b/guides/source/command_line.md
@@ -102,6 +102,7 @@ Please choose a generator below.
 
 Rails:
   assets
+  channel
   controller
   generator
   ...
@@ -241,6 +242,8 @@ $ bin/rails generate scaffold HighScore game:string score:integer
     invoke    jbuilder
     create      app/views/high_scores/index.json.jbuilder
     create      app/views/high_scores/show.json.jbuilder
+    invoke  test_unit
+    create    test/system/high_scores_test.rb
     invoke  assets
     invoke    coffee
     create      app/assets/javascripts/high_scores.coffee
@@ -642,13 +645,16 @@ $ cat config/database.yml
 # Configure Using Gemfile
 # gem 'pg'
 #
-development:
+default: &default
   adapter: postgresql
   encoding: unicode
+  # For details on connection pooling, see Rails configuration guide
+  # http://guides.rubyonrails.org/configuring.html#database-pooling
+  pool: <%= ENV.fetch("RAILS_MAX_THREADS") { 5 } %>
+
+development:
+  <<: *default
   database: gitapp_development
-  pool: 5
-  username: gitapp
-  password:
 ...
 ...
 ```
diff --git a/guides/source/contributing_to_ruby_on_rails.md b/guides/source/contributing_to_ruby_on_rails.md
index 2f2962a3e6..959cd3ea1c 100644
--- a/guides/source/contributing_to_ruby_on_rails.md
+++ b/guides/source/contributing_to_ruby_on_rails.md
@@ -164,7 +164,7 @@ NOTE: The instructions are for Rails > 4. The Redcarpet Gem doesn't work with JR
 Translation efforts we know about (various versions):
 
 * **Italian**: [https://github.com/rixlabs/docrails](https://github.com/rixlabs/docrails)
-* **Spanish**: [http://wiki.github.com/gramos/docrails](http://wiki.github.com/gramos/docrails)
+* **Spanish**: [https://wiki.github.com/gramos/docrails](https://wiki.github.com/gramos/docrails)
 * **Polish**: [https://github.com/apohllo/docrails/tree/master](https://github.com/apohllo/docrails/tree/master)
 * **French** : [https://github.com/railsfrance/docrails](https://github.com/railsfrance/docrails)
 * **Czech** : [https://github.com/rubyonrails-cz/docrails/tree/czech](https://github.com/rubyonrails-cz/docrails/tree/czech)
@@ -324,7 +324,7 @@ file.
 
 #### Testing Active Record
 
-First, create the databases you'll need. You can find a list of the required 
+First, create the databases you'll need. You can find a list of the required
 table names, usernames, and passwords in `activerecord/test/config.example.yml`.
 
 For MySQL and PostgreSQL, running the SQL statements `create database
diff --git a/guides/source/debugging_rails_applications.md b/guides/source/debugging_rails_applications.md
index 58aab774b3..99bc7c5fb5 100644
--- a/guides/source/debugging_rails_applications.md
+++ b/guides/source/debugging_rails_applications.md
@@ -162,41 +162,41 @@ class ArticlesController < ApplicationController
   # ...
 
   def create
-    @article = Article.new(params[:article])
+    @article = Article.new(article_params)
     logger.debug "New article: #{@article.attributes.inspect}"
     logger.debug "Article should be valid: #{@article.valid?}"
 
     if @article.save
-      flash[:notice] =  'Article was successfully created.'
       logger.debug "The article was saved and now the user is going to be redirected..."
-      redirect_to(@article)
+      redirect_to @article, notice: 'Article was successfully created.'
     else
-      render action: "new"
+      render :new
     end
   end
 
   # ...
+
+  private
+    def article_params
+      params.require(:article).permit(:title, :body, :published)
+    end
 end
 ```
 
 Here's an example of the log generated when this controller action is executed:
 
 ```
-Processing ArticlesController#create (for 127.0.0.1 at 2008-09-08 11:52:54) [POST]
-  Session ID: BAh7BzoMY3NyZl9pZCIlMDY5MWU1M2I1ZDRjODBlMzkyMWI1OTg2NWQyNzViZjYiCmZsYXNoSUM6J0FjdGl
-vbkNvbnRyb2xsZXI6OkZsYXNoOjpGbGFzaEhhc2h7AAY6CkB1c2VkewA=--b18cd92fba90eacf8137e5f6b3b06c4d724596a4
-  Parameters: {"commit"=>"Create", "article"=>{"title"=>"Debugging Rails",
- "body"=>"I'm learning how to print in logs!!!", "published"=>"0"},
- "authenticity_token"=>"2059c1286e93402e389127b1153204e0d1e275dd", "action"=>"create", "controller"=>"articles"}
-New article: {"updated_at"=>nil, "title"=>"Debugging Rails", "body"=>"I'm learning how to print in logs!!!",
- "published"=>false, "created_at"=>nil}
+Started POST "/articles" for 127.0.0.1 at 2017-08-20 20:53:10 +0900
+Processing by ArticlesController#create as HTML
+  Parameters: {"utf8"=>"✓", "authenticity_token"=>"xhuIbSBFytHCE1agHgvrlKnSVIOGD6jltW2tO+P6a/ACjQ3igjpV4OdbsZjIhC98QizWH9YdKokrqxBCJrtoqQ==", "article"=>{"title"=>"Debugging Rails", "body"=>"I'm learning how to print in logs!!!", "published"=>"0"}, "commit"=>"Create Article"}
+New article: {"id"=>nil, "title"=>"Debugging Rails", "body"=>"I'm learning how to print in logs!!!", "published"=>false, "created_at"=>nil, "updated_at"=>nil}
 Article should be valid: true
-  Article Create (0.000443)   INSERT INTO "articles" ("updated_at", "title", "body", "published",
- "created_at") VALUES('2008-09-08 14:52:54', 'Debugging Rails',
- 'I''m learning how to print in logs!!!', 'f', '2008-09-08 14:52:54')
+   (0.1ms)  BEGIN
+  SQL (0.4ms)  INSERT INTO "articles" ("title", "body", "published", "created_at", "updated_at") VALUES ($1, $2, $3, $4, $5) RETURNING "id"  [["title", "Debugging Rails"], ["body", "I'm learning how to print in logs!!!"], ["published", "f"], ["created_at", "2017-08-20 11:53:10.010435"], ["updated_at", "2017-08-20 11:53:10.010435"]]
+   (0.3ms)  COMMIT
 The article was saved and now the user is going to be redirected...
-Redirected to # Article:0x20af760>
-Completed in 0.01224 (81 reqs/sec) | DB: 0.00044 (3%) | 302 Found [http://localhost/articles]
+Redirected to http://localhost:3000/articles/1
+Completed 302 Found in 4ms (ActiveRecord: 0.8ms)
 ```
 
 Adding extra logging like this makes it easy to search for unexpected or unusual behavior in your logs. If you add extra logging, be sure to make sensible use of log levels to avoid filling your production logs with useless trivia.
@@ -542,7 +542,7 @@ command later in this guide).
    9
 => 10       respond_to do |format|
    11         format.html # index.html.erb
-   12        format.json { render json: @articles }
+   12         format.json { render json: @articles }
    13      end
    14    end
    15
diff --git a/guides/source/development_dependencies_install.md b/guides/source/development_dependencies_install.md
index c57efd6362..5a9729bb0f 100644
--- a/guides/source/development_dependencies_install.md
+++ b/guides/source/development_dependencies_install.md
@@ -21,24 +21,25 @@ The easiest and recommended way to get a development environment ready to hack i
 The Hard Way
 ------------
 
-In case you can't use the Rails development box, see section below, these are the steps to manually build a development box for Ruby on Rails core development.
+In case you can't use the Rails development box, see the steps below to manually
+build a development box for Ruby on Rails core development.
 
 ### Install Git
 
-Ruby on Rails uses Git for source code control. The [Git homepage](http://git-scm.com/) has installation instructions. There are a variety of resources on the net that will help you get familiar with Git:
+Ruby on Rails uses Git for source code control. The [Git homepage](https://git-scm.com/) has installation instructions. There are a variety of resources on the net that will help you get familiar with Git:
 
-* [Try Git course](http://try.github.io/) is an interactive course that will teach you the basics.
-* The [official Documentation](http://git-scm.com/documentation) is pretty comprehensive and also contains some videos with the basics of Git.
-* [Everyday Git](http://schacon.github.io/git/everyday.html) will teach you just enough about Git to get by.
-* [GitHub](http://help.github.com) offers links to a variety of Git resources.
-* [Pro Git](http://git-scm.com/book) is an entire book about Git with a Creative Commons license.
+* [Try Git course](https://try.github.io/) is an interactive course that will teach you the basics.
+* The [official Documentation](https://git-scm.com/documentation) is pretty comprehensive and also contains some videos with the basics of Git.
+* [Everyday Git](https://schacon.github.io/git/everyday.html) will teach you just enough about Git to get by.
+* [GitHub](https://help.github.com/) offers links to a variety of Git resources.
+* [Pro Git](https://git-scm.com/book) is an entire book about Git with a Creative Commons license.
 
 ### Clone the Ruby on Rails Repository
 
 Navigate to the folder where you want the Ruby on Rails source code (it will create its own `rails` subdirectory) and run:
 
 ```bash
-$ git clone git://github.com/rails/rails.git
+$ git clone https://github.com/rails/rails.git
 $ cd rails
 ```
 
@@ -62,7 +63,7 @@ $ sudo apt-get install sqlite3 libsqlite3-dev
 If you are on Fedora or CentOS, you're done with
 
 ```bash
-$ sudo yum install libsqlite3x libsqlite3x-devel 
+$ sudo yum install libsqlite3x libsqlite3x-devel
 ```
 
 If you are on Arch Linux, you will need to run:
@@ -96,7 +97,7 @@ This command will install all dependencies except the MySQL and PostgreSQL Ruby
 
 NOTE: If you would like to run the tests that use memcached, you need to ensure that you have it installed and running.
 
-You can use [Homebrew](http://brew.sh/) to install memcached on OS X:
+You can use [Homebrew](https://brew.sh/) to install memcached on macOS:
 
 ```bash
 $ brew install memcached
@@ -181,7 +182,7 @@ The Active Record test suite requires a custom config file: `activerecord/test/c
 To be able to run the suite for MySQL and PostgreSQL we need their gems. Install
 first the servers, their client libraries, and their development files.
 
-On OS X, you can run:
+On macOS, you can run:
 
 ```bash
 $ brew install mysql
@@ -190,7 +191,7 @@ $ brew install postgresql
 
 Follow the instructions given by Homebrew to start these.
 
-In Ubuntu just run:
+On Ubuntu, just run:
 
 ```bash
 $ sudo apt-get install mysql-server libmysqlclient-dev
@@ -260,34 +261,34 @@ with your development account, on Linux or BSD, you just have to run:
 $ sudo -u postgres createuser --superuser $USER
 ```
 
-and for OS X:
+and for macOS:
 
 ```bash
 $ createuser --superuser $USER
 ```
 
-Then you need to create the test databases with
+Then, you need to create the test databases with:
 
 ```bash
 $ cd activerecord
 $ bundle exec rake db:postgresql:build
 ```
 
-It is possible to build databases for both PostgreSQL and MySQL with
+It is possible to build databases for both PostgreSQL and MySQL with:
 
 ```bash
 $ cd activerecord
 $ bundle exec rake db:create
 ```
 
-You can cleanup the databases using
+You can cleanup the databases using:
 
 ```bash
 $ cd activerecord
 $ bundle exec rake db:drop
 ```
 
-NOTE: Using the rake task to create the test databases ensures they have the correct character set and collation.
+NOTE: Using the Rake task to create the test databases ensures they have the correct character set and collation.
 
 NOTE: You'll see the following warning (or localized warning) during activating HStore extension in PostgreSQL 9.1.x or earlier: "WARNING: => is deprecated as an operator".
 
@@ -299,11 +300,11 @@ Action Cable uses Redis as its default subscriptions adapter ([read more](action
 
 #### Install Redis From Source
 
-Redis' documentation discourage installations with package managers as those are usually outdated. Installing from source and bringing the server up is straight forward and well documented on [Redis' documentation](http://redis.io/download#installation).
+Redis' documentation discourage installations with package managers as those are usually outdated. Installing from source and bringing the server up is straight forward and well documented on [Redis' documentation](https://redis.io/download#installation).
 
 #### Install Redis From Package Manager
 
-On OS X, you can run:
+On macOS, you can run:
 
 ```bash
 $ brew install redis
@@ -311,7 +312,7 @@ $ brew install redis
 
 Follow the instructions given by Homebrew to start these.
 
-In Ubuntu just run:
+On Ubuntu, just run:
 
 ```bash
 $ sudo apt-get install redis-server
@@ -323,7 +324,7 @@ On Fedora or CentOS (requires EPEL enabled), just run:
 $ sudo yum install redis
 ```
 
-If you are running Arch Linux just run:
+If you are running Arch Linux, just run:
 
 ```bash
 $ sudo pacman -S redis
@@ -335,3 +336,43 @@ FreeBSD users will have to run the following:
 ```bash
 # portmaster databases/redis
 ```
+
+### Active Storage Setup
+
+When working on Active Storage, it is important to note that you need to
+install its JavaScript dependencies while working on that section of the
+codebase. In order to install these dependencies, it is necessary to
+have Yarn, a Node.js package manager, available on your system. A
+prerequisite for installing this package manager is that
+[Node.js](https://nodejs.org) is installed.
+
+
+On macOS, you can run:
+
+```bash
+brew install yarn
+```
+
+On Ubuntu, you can run:
+
+```bash
+curl -sS https://dl.yarnpkg.com/debian/pubkey.gpg | sudo apt-key add -
+echo "deb https://dl.yarnpkg.com/debian/ stable main" | sudo tee /etc/apt/sources.list.d/yarn.list
+
+sudo apt-get update && sudo apt-get install yarn
+```
+
+On Fedora or CentOS, just run:
+
+```bash
+sudo wget https://dl.yarnpkg.com/rpm/yarn.repo -O /etc/yum.repos.d/yarn.repo
+
+sudo yum install yarn
+```
+
+Finally, after installing Yarn, you will need to run the following
+command inside of the `activestorage` directory to install the dependencies:
+
+```bash
+yarn install
+```
diff --git a/guides/source/engines.md b/guides/source/engines.md
index 2276f348a1..c7331b6ca4 100644
--- a/guides/source/engines.md
+++ b/guides/source/engines.md
@@ -346,6 +346,9 @@ invoke    test_unit
 create      test/controllers/blorgh/articles_controller_test.rb
 invoke    helper
 create      app/helpers/blorgh/articles_helper.rb
+invoke  test_unit
+create    test/application_system_test_case.rb
+create    test/system/articles_test.rb
 invoke  assets
 invoke    js
 create      app/assets/javascripts/blorgh/articles.js
diff --git a/guides/source/generators.md b/guides/source/generators.md
index 389224d908..37af7a1310 100644
--- a/guides/source/generators.md
+++ b/guides/source/generators.md
@@ -197,6 +197,9 @@ $ bin/rails generate scaffold User name:string
       invoke    jbuilder
       create      app/views/users/index.json.jbuilder
       create      app/views/users/show.json.jbuilder
+      invoke  test_unit
+      create    test/application_system_test_case.rb
+      create    test/system/users_test.rb
       invoke  assets
       invoke    coffee
       create      app/assets/javascripts/users.coffee
@@ -415,6 +418,9 @@ $ bin/rails generate scaffold Comment body:text
       invoke    jbuilder
       create      app/views/comments/index.json.jbuilder
       create      app/views/comments/show.json.jbuilder
+      invoke  test_unit
+      create    test/application_system_test_case.rb
+      create    test/system/comments_test.rb
       invoke  assets
       invoke    coffee
       create      app/assets/javascripts/comments.coffee
diff --git a/guides/source/initialization.md b/guides/source/initialization.md
index ccad10f07d..0cfabe2a66 100644
--- a/guides/source/initialization.md
+++ b/guides/source/initialization.md
@@ -99,13 +99,15 @@ configure the load path for your Gemfile's dependencies.
 
 A standard Rails application depends on several gems, specifically:
 
+* actioncable
 * actionmailer
 * actionpack
 * actionview
+* activejob
 * activemodel
 * activerecord
+* activestorage
 * activesupport
-* activejob
 * arel
 * builder
 * bundler
@@ -131,7 +133,7 @@ Once `config/boot.rb` has finished, the next file that is required is
 `ARGV` array simply contains `server` which will be passed over:
 
 ```ruby
-require "rails/command"
+require_relative "command"
 
 aliases = {
   "g"  => "generate",
@@ -170,7 +172,7 @@ module Rails::Command
       namespace = namespace.to_s
       namespace = "help" if namespace.blank? || HELP_MAPPINGS.include?(namespace)
       namespace = "version" if %w( -v --version ).include? namespace
-    
+
       if command = find_by_namespace(namespace)
         command.perform(namespace, args, config)
       else
@@ -189,7 +191,7 @@ module Rails
     class ServerCommand < Base # :nodoc:
       def perform
         set_application_directory!
-  
+
         Rails::Server.new.tap do |server|
           # Require application after server sets environment to propagate
           # the --environment option.
@@ -311,7 +313,7 @@ def parse!(args)
   args, options = args.dup, {}
 
   option_parser(options).parse! args
-  
+
   options[:log_stdout] = options[:daemonize].blank? && (options[:environment] || Rails.env) == "development"
   options[:server]     = args.shift
   options
@@ -366,11 +368,11 @@ private
 
   def log_to_stdout
     wrapped_app # touch the app so the logger is set up
-  
+
     console = ActiveSupport::Logger.new(STDOUT)
     console.formatter = Rails.logger.formatter
     console.level = Rails.logger.level
-  
+
     unless ActiveSupport::Logger.logger_outputs_to?(Rails.logger, STDOUT)
       Rails.logger.extend(ActiveSupport::Logger.broadcast(console))
     end
@@ -537,6 +539,7 @@ require "rails"
   action_mailer/railtie
   active_job/railtie
   action_cable/engine
+  active_storage/engine
   rails/test_unit/railtie
   sprockets/railtie
 ).each do |railtie|
diff --git a/guides/source/plugins.md b/guides/source/plugins.md
index 8c2d56ceb8..164207a9f9 100644
--- a/guides/source/plugins.md
+++ b/guides/source/plugins.md
@@ -74,7 +74,7 @@ In this example you will add a method to String named `to_squawk`. To begin, cre
 ```ruby
 # yaffle/test/core_ext_test.rb
 
-require 'test_helper'
+require "test_helper"
 
 class CoreExtTest < ActiveSupport::TestCase
   def test_to_squawk_prepends_the_word_squawk
@@ -104,14 +104,16 @@ Finished in 0.003358s, 595.6483 runs/s, 297.8242 assertions/s.
 
 Great - now you are ready to start development.
 
-In `lib/yaffle.rb`, add `require 'yaffle/core_ext'`:
+In `lib/yaffle.rb`, add `require "yaffle/core_ext"`:
 
 ```ruby
 # yaffle/lib/yaffle.rb
 
-require 'yaffle/core_ext'
+require "yaffle/railtie"
+require "yaffle/core_ext"
 
 module Yaffle
+  # Your code goes here...
 end
 ```
 
@@ -120,7 +122,7 @@ Finally, create the `core_ext.rb` file and add the `to_squawk` method:
 ```ruby
 # yaffle/lib/yaffle/core_ext.rb
 
-String.class_eval do
+class String
   def to_squawk
     "squawk! #{self}".strip
   end
@@ -152,7 +154,7 @@ To begin, set up your files so that you have:
 ```ruby
 # yaffle/test/acts_as_yaffle_test.rb
 
-require 'test_helper'
+require "test_helper"
 
 class ActsAsYaffleTest < ActiveSupport::TestCase
 end
@@ -161,10 +163,12 @@ end
 ```ruby
 # yaffle/lib/yaffle.rb
 
-require 'yaffle/core_ext'
-require 'yaffle/acts_as_yaffle'
+require "yaffle/railtie"
+require "yaffle/core_ext"
+require "yaffle/acts_as_yaffle"
 
 module Yaffle
+  # Your code goes here...
 end
 ```
 
@@ -173,7 +177,6 @@ end
 
 module Yaffle
   module ActsAsYaffle
-    # your code will go here
   end
 end
 ```
@@ -189,7 +192,7 @@ To start out, write a failing test that shows the behavior you'd like:
 ```ruby
 # yaffle/test/acts_as_yaffle_test.rb
 
-require 'test_helper'
+require "test_helper"
 
 class ActsAsYaffleTest < ActiveSupport::TestCase
   def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
@@ -276,12 +279,8 @@ module Yaffle
   module ActsAsYaffle
     extend ActiveSupport::Concern
 
-    included do
-    end
-
-    module ClassMethods
+    class_methods do
       def acts_as_yaffle(options = {})
-        # your code will go here
       end
     end
   end
@@ -335,10 +334,7 @@ module Yaffle
   module ActsAsYaffle
     extend ActiveSupport::Concern
 
-    included do
-    end
-
-    module ClassMethods
+    class_methods do
       def acts_as_yaffle(options = {})
         cattr_accessor :yaffle_text_field, default: (options[:yaffle_text_field] || :last_squawk).to_s
       end
@@ -370,7 +366,7 @@ To start out, write a failing test that shows the behavior you'd like:
 
 ```ruby
 # yaffle/test/acts_as_yaffle_test.rb
-require 'test_helper'
+require "test_helper"
 
 class ActsAsYaffleTest < ActiveSupport::TestCase
   def test_a_hickwalls_yaffle_text_field_should_be_last_squawk
@@ -406,19 +402,14 @@ module Yaffle
     extend ActiveSupport::Concern
 
     included do
+      def squawk(string)
+        write_attribute(self.class.yaffle_text_field, string.to_squawk)
+      end
     end
 
-    module ClassMethods
+    class_methods do
       def acts_as_yaffle(options = {})
         cattr_accessor :yaffle_text_field, default: (options[:yaffle_text_field] || :last_squawk).to_s
-
-        include Yaffle::ActsAsYaffle::LocalInstanceMethods
-      end
-    end
-
-    module LocalInstanceMethods
-      def squawk(string)
-        write_attribute(self.class.yaffle_text_field, string.to_squawk)
       end
     end
   end
@@ -449,7 +440,7 @@ Generators
 ----------
 
 Generators can be included in your gem simply by creating them in a lib/generators directory of your plugin. More information about
-the creation of generators can be found in the [Generators Guide](generators.html)
+the creation of generators can be found in the [Generators Guide](generators.html).
 
 Publishing Your Gem
 -------------------
@@ -458,13 +449,13 @@ Gem plugins currently in development can easily be shared from any Git repositor
 commit the code to a Git repository (like GitHub) and add a line to the Gemfile of the application in question:
 
 ```ruby
-gem 'yaffle', git: 'git://github.com/yaffle_watcher/yaffle.git'
+gem "yaffle", git: "https://github.com/rails/yaffle.git"
 ```
 
 After running `bundle install`, your gem functionality will be available to the application.
 
-When the gem is ready to be shared as a formal release, it can be published to [RubyGems](http://www.rubygems.org).
-For more information about publishing gems to RubyGems, see: [Creating and Publishing Your First Ruby Gem](http://blog.thepete.net/2010/11/creating-and-publishing-your-first-ruby.html).
+When the gem is ready to be shared as a formal release, it can be published to [RubyGems](https://rubygems.org).
+For more information about publishing gems to RubyGems, see: [Publishing your gem](http://guides.rubygems.org/publishing).
 
 RDoc Documentation
 ------------------
@@ -478,7 +469,7 @@ The first step is to update the README file with detailed information about how
 * How to add the functionality to the app (several examples of common use cases)
 * Warnings, gotchas or tips that might help users and save them time
 
-Once your README is solid, go through and add rdoc comments to all of the methods that developers will use. It's also customary to add '#:nodoc:' comments to those parts of the code that are not included in the public API.
+Once your README is solid, go through and add rdoc comments to all of the methods that developers will use. It's also customary to add `#:nodoc:` comments to those parts of the code that are not included in the public API.
 
 Once your comments are good to go, navigate to your plugin directory and run:
 
diff --git a/guides/source/rails_on_rack.md b/guides/source/rails_on_rack.md
index cef8450ee4..00020a0ea5 100644
--- a/guides/source/rails_on_rack.md
+++ b/guides/source/rails_on_rack.md
@@ -302,7 +302,7 @@ Resources
 
 ### Learning Rack
 
-* [Official Rack Website](http://rack.github.io)
+* [Official Rack Website](https://rack.github.io)
 * [Introducing Rack](http://chneukirchen.org/blog/archive/2007/02/introducing-rack.html)
 
 ### Understanding Middlewares
diff --git a/guides/source/security.md b/guides/source/security.md
index 297680b176..7736a4b224 100644
--- a/guides/source/security.md
+++ b/guides/source/security.md
@@ -1025,7 +1025,7 @@ Here is a list of common headers:
 * **X-Content-Type-Options:** _'nosniff' in Rails by default_ - stops the browser from guessing the MIME type of a file.
 * **X-Content-Security-Policy:** [A powerful mechanism for controlling which sites certain content types can be loaded from](http://w3c.github.io/webappsec/specs/content-security-policy/csp-specification.dev.html)
 * **Access-Control-Allow-Origin:** Used to control which sites are allowed to bypass same origin policies and send cross-origin requests.
-* **Strict-Transport-Security:** [Used to control if the browser is allowed to only access a site over a secure connection](http://en.wikipedia.org/wiki/HTTP_Strict_Transport_Security)
+* **Strict-Transport-Security:** [Used to control if the browser is allowed to only access a site over a secure connection](https://en.wikipedia.org/wiki/HTTP_Strict_Transport_Security)
 
 Environmental Security
 ----------------------
@@ -1060,7 +1060,7 @@ Additional Resources
 
 The security landscape shifts and it is important to keep up to date, because missing a new vulnerability can be catastrophic. You can find additional resources about (Rails) security here:
 
-* Subscribe to the Rails security [mailing list.](http://groups.google.com/group/rubyonrails-security)
-* [Brakeman - Rails Security Scanner](http://brakemanscanner.org/) - To perform static security analysis for Rails applications.
-* [Keep up to date on the other application layers.](http://secunia.com/) (they have a weekly newsletter, too)
-* A [good security blog](https://www.owasp.org) including the [Cross-Site scripting Cheat Sheet.](https://www.owasp.org/index.php/DOM_based_XSS_Prevention_Cheat_Sheet)
+* Subscribe to the Rails security [mailing list](https://groups.google.com/forum/#!forum/rubyonrails-security).
+* [Brakeman - Rails Security Scanner](https://brakemanscanner.org/) - To perform static security analysis for Rails applications.
+* [Keep up to date on the other application layers](http://secunia.com/) (they have a weekly newsletter, too).
+* A [good security blog](https://www.owasp.org) including the [Cross-Site scripting Cheat Sheet](https://www.owasp.org/index.php/DOM_based_XSS_Prevention_Cheat_Sheet).
diff --git a/guides/source/testing.md b/guides/source/testing.md
index 1c648ac47f..8141713e1e 100644
--- a/guides/source/testing.md
+++ b/guides/source/testing.md
@@ -367,9 +367,10 @@ All the basic assertions such as `assert_equal` defined in `Minitest::Assertions
 * [`ActiveSupport::TestCase`](http://api.rubyonrails.org/classes/ActiveSupport/TestCase.html)
 * [`ActionMailer::TestCase`](http://api.rubyonrails.org/classes/ActionMailer/TestCase.html)
 * [`ActionView::TestCase`](http://api.rubyonrails.org/classes/ActionView/TestCase.html)
-* [`ActionDispatch::IntegrationTest`](http://api.rubyonrails.org/classes/ActionDispatch/IntegrationTest.html)
 * [`ActiveJob::TestCase`](http://api.rubyonrails.org/classes/ActiveJob/TestCase.html)
+* [`ActionDispatch::IntegrationTest`](http://api.rubyonrails.org/classes/ActionDispatch/IntegrationTest.html)
 * [`ActionDispatch::SystemTestCase`](http://api.rubyonrails.org/classes/ActionDispatch/SystemTestCase.html)
+* [`Rails::Generators::TestCase`](http://api.rubyonrails.org/classes/Rails/Generators/TestCase.html)
 
 Each of these classes include `Minitest::Assertions`, allowing us to use all of the basic assertions in our tests.
 
@@ -451,7 +452,8 @@ You can run multiple files and directories at the same time:
 By default test failures and errors are reported inline during a run.
 
 Rails options:
-    -e, --environment ENV            Run tests in the ENV environment
+    -w, --warnings                   Run with Ruby warnings enabled
+    -e, --environment                Run tests in the ENV environment
     -b, --backtrace                  Show the complete backtrace
     -d, --defer-output               Output test failures and errors after the test run
     -f, --fail-fast                  Abort test run on first failure or error
diff --git a/guides/source/upgrading_ruby_on_rails.md b/guides/source/upgrading_ruby_on_rails.md
index 6e927d7244..651b86275a 100644
--- a/guides/source/upgrading_ruby_on_rails.md
+++ b/guides/source/upgrading_ruby_on_rails.md
@@ -278,7 +278,7 @@ You can now just call the dependency once with a wildcard.
 
 ### `ActionView::Helpers::RecordTagHelper` moved to external gem (record_tag_helper)
 
-`content_tag_for` and `div_for` has been removed in favor of just using `content_tag`. To continue using it, add the `record_tag_helper` gem to your Gemfile:
+`content_tag_for` and `div_for` have been removed in favor of just using `content_tag`. To continue using the older methods, add the `record_tag_helper` gem to your Gemfile:
 
 ```ruby
 gem 'record_tag_helper', '~> 1.0'
@@ -397,6 +397,15 @@ When using Ruby 2.4, you can preserve the timezone of the receiver when calling
 
     ActiveSupport.to_time_preserves_timezone = false
 
+### Changes with JSON/JSONB serialization
+
+In Rails 5.0, how JSON/JSONB attributes are serialized and deserialized changed. Now, if
+you set a column equal to a `String`, Active Record will no longer turn that string
+into a `Hash`, and will instead only return the string. This is not limited to code
+interacting with models, but also affects `:default` column settings in `db/schema.rb`.
+It is recommended that you do not set columns equal to a `String`, but pass a `Hash`
+instead, which will be converted to and from a JSON string automatically.
+
 Upgrading from Rails 4.1 to Rails 4.2
 -------------------------------------