7 files changed, 91 insertions, 18 deletions
diff --git a/guides/source/5_0_release_notes.md b/guides/source/5_0_release_notes.md
index f5abbd0cd4..dc631e5cb9 100644
--- a/guides/source/5_0_release_notes.md
+++ b/guides/source/5_0_release_notes.md
@@ -256,6 +256,12 @@ Please refer to the [Changelog][action-pack] for detailed changes.
 *   Rails will only generate "weak", instead of strong ETags.
     ([Pull Request](https://github.com/rails/rails/pull/17573))
 
+*   Controller actions without an explicit `render` call and with no
+    corresponding templates will render `head :no_content` implicitly
+    instead of raising an error.
+    (Pull Request [1](https://github.com/rails/rails/pull/19377),
+    [2](https://github.com/rails/rails/pull/23827))
+
 Action View
 -------------
 
@@ -316,6 +322,9 @@ Please refer to the [Changelog][action-mailer] for detailed changes.
 *   Template lookup now respects default locale and I18n fallbacks.
     ([commit](https://github.com/rails/rails/commit/ecb1981b))
 
+*   Template can use fragment cache like Action View template.
+    ([Pull Request](https://github.com/rails/rails/pull/22825))
+
 *   Added `_mailer` suffix to mailers created via generator, following the same
     naming convention used in controllers and jobs.
     ([Pull Request](https://github.com/rails/rails/pull/18074))
@@ -327,6 +336,9 @@ Please refer to the [Changelog][action-mailer] for detailed changes.
     the mailer queue name.
     ([Pull Request](https://github.com/rails/rails/pull/18587))
 
+*   Added `config.action_mailer.perform_caching` configuration to determine whether your templates should perform caching or not.
+    ([Pull Request](https://github.com/rails/rails/pull/22825))
+
 
 Active Record
 -------------
diff --git a/guides/source/action_mailer_basics.md b/guides/source/action_mailer_basics.md
index 91ea4efb55..558c16f5b0 100644
--- a/guides/source/action_mailer_basics.md
+++ b/guides/source/action_mailer_basics.md
@@ -407,6 +407,22 @@ use the rendered text for the text part. The render command is the same one used
 inside of Action Controller, so you can use all the same options, such as
 `:text`, `:inline` etc.
 
+#### Caching mailer view
+
+You can do cache in mailer views like in application views using `cache` method.
+
+```
+<% cache do %>
+  <%= @company.name %>
+<% end %>
+```
+
+And in order to use this feature, you need to configure your application with this:
+
+```
+  config.action_mailer.perform_caching = true
+```
+
 ### Action Mailer Layouts
 
 Just like controller views, you can also have mailer layouts. The layout name
diff --git a/guides/source/action_view_overview.md b/guides/source/action_view_overview.md
index 5e6eae1071..29e0943741 100644
--- a/guides/source/action_view_overview.md
+++ b/guides/source/action_view_overview.md
@@ -599,7 +599,7 @@ This would add something like "Process data files (0.34523)" to the log, which y
 
 #### cache
 
-A method for caching fragments of a view rather than an entire action or page. This technique is useful for caching pieces like menus, lists of news topics, static HTML fragments, and so on. This method takes a block that contains the content you wish to cache. See `ActionController::Caching::Fragments` for more information.
+A method for caching fragments of a view rather than an entire action or page. This technique is useful for caching pieces like menus, lists of news topics, static HTML fragments, and so on. This method takes a block that contains the content you wish to cache. See `AbstractController::Caching::Fragments` for more information.
 
 ```erb
 <% cache do %>
diff --git a/guides/source/api_app.md b/guides/source/api_app.md
index 0598b9c7fa..8dba914923 100644
--- a/guides/source/api_app.md
+++ b/guides/source/api_app.md
@@ -166,6 +166,23 @@ class definition:
 config.api_only = true
 ```
 
+In `config/environments/development.rb`, set `config.debug_exception_response_format`
+to configure the format used in responses when errors occur in development mode.
+
+To render an HTML page with debugging information, use the value `:default`.
+
+```ruby
+config.debug_exception_response_format = :default
+```
+
+To render debugging information preserving the response format, use the value `:api`.
+
+```ruby
+config.debug_exception_response_format = :api
+```
+
+By default, `config.debug_exception_response_format` is set to `:api`.
+
 Finally, inside `app/controllers/application_controller.rb`, instead of:
 
 ```ruby
diff --git a/guides/source/caching_with_rails.md b/guides/source/caching_with_rails.md
index 3a1a1ccfe6..f26019c72e 100644
--- a/guides/source/caching_with_rails.md
+++ b/guides/source/caching_with_rails.md
@@ -521,6 +521,14 @@ class ProductsController < ApplicationController
 end
 ```
 
+### A note on weak ETags
+
+Etags generated by Rails are weak by default. Weak etags allow symantically equivalent responses to have the same etags, even if their bodies do not match exactly. This is useful when we don't want the page to be regenerated for minor changes in response body. If you absolutely need to generate a strong etag, it can be assigned to the header directly.
+
+```ruby
+  response.add_header "ETag", Digest::MD5.hexdigest(response.body)
+```
+
 References
 ----------
 
diff --git a/guides/source/configuring.md b/guides/source/configuring.md
index a5fb396f15..b83d25c683 100644
--- a/guides/source/configuring.md
+++ b/guides/source/configuring.md
@@ -98,13 +98,15 @@ application. Accepts a valid week day symbol (e.g. `:monday`).
 
 * `config.exceptions_app` sets the exceptions application invoked by the ShowException middleware when an exception happens. Defaults to `ActionDispatch::PublicExceptions.new(Rails.public_path)`.
 
+* `config.debug_exception_response_format` sets the format used in responses when errors occur in development mode.
+
 * `config.file_watcher` is the class used to detect file updates in the file system when `config.reload_classes_only_on_change` is true. Rails ships with `ActiveSupport::FileUpdateChecker`, the default, and `ActiveSupport::EventedFileUpdateChecker` (this one depends on the [listen](https://github.com/guard/listen) gem). Custom classes must conform to the `ActiveSupport::FileUpdateChecker` API.
 
 * `config.filter_parameters` used for filtering out the parameters that
 you don't want shown in the logs, such as passwords or credit card
 numbers. New applications filter out passwords by adding the following `config.filter_parameters+=[:password]` in `config/initializers/filter_parameter_logging.rb`.
 
-* `config.force_ssl` forces all requests to be served over HTTPS by using the `ActionDispatch::SSL` middleware. This can be configured by setting `config.ssl_options` - see the [ActionDispatch::SSL documentation](http://edgeapi.rubyonrails.org/classes/ActionDispatch/SSL.html) for details.
+* `config.force_ssl` forces all requests to be served over HTTPS by using the `ActionDispatch::SSL` middleware, and sets `config.action_mailer.default_url_options` to be `{ protocol: 'https' }`. This can be configured by setting `config.ssl_options` - see the [ActionDispatch::SSL documentation](http://edgeapi.rubyonrails.org/classes/ActionDispatch/SSL.html) for details.
 
 * `config.log_formatter` defines the formatter of the Rails logger. This option defaults to an instance of `ActiveSupport::Logger::SimpleFormatter` for all modes except production, where it defaults to `Logger::Formatter`.
 
@@ -531,6 +533,9 @@ There are a number of settings available on `config.action_mailer`:
 * `config.action_mailer.deliver_later_queue_name` specifies the queue name for
   mailers. By default this is `mailers`.
 
+* `config.action_mailer.perform_caching` specifies whether the mailer templates should perform fragment caching or not. By default this is false in all environments.
+
+
 ### Configuring Active Support
 
 There are a few configuration options available in Active Support:
@@ -610,6 +615,17 @@ There are a few configuration options available in Active Support:
 
 * `config.active_job.logger` accepts a logger conforming to the interface of Log4r or the default Ruby Logger class, which is then used to log information from Active Job. You can retrieve this logger by calling `logger` on either an Active Job class or an Active Job instance. Set to `nil` to disable logging.
 
+### Configuring Action Cable
+
+* `config.action_cable.url` accepts a string for the URL for where
+ you are hosting your Action Cable server. You would use this option
+if you are running Action Cable servers that are separated from your
+main application.
+* `config.action_cable.mount_path` accepts a string for where to mount Action
+  Cable, as apart of the main server process. Defaults to `/cable`.
+You can set this as nil to not mount Action Cable as apart of your
+normal Rails server.
+
 ### Configuring a Database
 
 Just about every Rails application will interact with a database. You can connect to the database by setting an environment variable `ENV['DATABASE_URL']` or by using a configuration file called `config/database.yml`.
diff --git a/guides/source/getting_started.md b/guides/source/getting_started.md
index 8eb3b6190f..4431512eda 100644
--- a/guides/source/getting_started.md
+++ b/guides/source/getting_started.md
@@ -298,26 +298,30 @@ Open the file `config/routes.rb` in your editor.
 Rails.application.routes.draw do
   get 'welcome/index'
 
-  # The priority is based upon order of creation:
-  # first created -> highest priority.
-  # See how all your routes lay out with "bin/rails routes".
-  #
-  # You can have the root of your site routed with "root"
-  # root 'welcome#index'
-  #
-  # ...
+  # For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html
+
+  # Serve websocket cable requests in-process
+  # mount ActionCable.server => '/cable'
+end
 ```
 
 This is your application's _routing file_ which holds entries in a special
 [DSL (domain-specific language)](http://en.wikipedia.org/wiki/Domain-specific_language)
 that tells Rails how to connect incoming requests to
-controllers and actions. This file contains many sample routes on commented
-lines, and one of them actually shows you how to connect the root of your site
-to a specific controller and action. Find the line beginning with `root` and
-uncomment it. It should look something like the following:
+controllers and actions.
+Edit this file by adding the line of code `root 'welcome#index'`.
+It should look something like the following:
 
 ```ruby
-root 'welcome#index'
+Rails.application.routes.draw do
+  get 'welcome/index'
+
+  # For details on the DSL available within this file, see http://guides.rubyonrails.org/routing.html
+
+  # Serve websocket cable requests in-process
+  # mount ActionCable.server => '/cable'
+  root 'welcome#index'
+end
 ```
 
 `root 'welcome#index'` tells Rails to map requests to the root of the
@@ -348,7 +352,7 @@ operations are referred to as _CRUD_ operations.
 
 Rails provides a `resources` method which can be used to declare a standard REST
 resource. You need to add the _article resource_ to the
-`config/routes.rb` as follows:
+`config/routes.rb` so the file will look as follows:
 
 ```ruby
 Rails.application.routes.draw do
@@ -625,7 +629,7 @@ end
 The `render` method here is taking a very simple hash with a key of `:plain` and
 value of `params[:article].inspect`. The `params` method is the object which
 represents the parameters (or fields) coming in from the form. The `params`
-method returns an `ActiveSupport::HashWithIndifferentAccess` object, which
+method returns an `ActionController::Parameters` object, which
 allows you to access the keys of the hash using either strings or symbols. In
 this situation, the only parameters that matter are the ones from the form.
 
@@ -635,7 +639,7 @@ If you re-submit the form one more time you'll now no longer get the missing
 template error. Instead, you'll see something that looks like the following:
 
 ```ruby
-{"title"=>"First article!", "text"=>"This is my first article."}
+<ActionController::Parameters {"title"=>"First Article!", "text"=>"This is my first article."} permitted: false>
 ```
 
 This action is now displaying the parameters for the article that are coming in