10 files changed, 80 insertions, 34 deletions
diff --git a/guides/source/6_0_release_notes.md b/guides/source/6_0_release_notes.md
index c826b19f1a..c152076628 100644
--- a/guides/source/6_0_release_notes.md
+++ b/guides/source/6_0_release_notes.md
@@ -513,7 +513,7 @@ Please refer to the [Changelog][active-record] for detailed changes.
     ([Pull Request](https://github.com/rails/rails/pull/34742))
 
 *   Add the ability to disable scopes generated by `ActiveRecord.enum`.
-    ([Pull Request](https://github.com/rails/rails/pull/34605/files))
+    ([Pull Request](https://github.com/rails/rails/pull/34605))
 
 *   Make implicit ordering configurable for a column.
     ([Pull Request](https://github.com/rails/rails/pull/34480))
diff --git a/guides/source/action_text_overview.md b/guides/source/action_text_overview.md
index 07919775e2..a735ec2b0e 100644
--- a/guides/source/action_text_overview.md
+++ b/guides/source/action_text_overview.md
@@ -46,6 +46,8 @@ happens after every keystroke, and avoids the need to use execCommand at all.
 ## Installation
 
 Run `rails action_text:install` to add the Yarn package and copy over the necessary migration.
+Also, you need to set up Active Storage for embedded images and other attachments.
+Please refer to the [Active Storage Overview](active_storage_overview.html) guide.
 
 ## Examples
 
diff --git a/guides/source/active_record_multiple_databases.md b/guides/source/active_record_multiple_databases.md
index 51f5cab2aa..07be21a254 100644
--- a/guides/source/active_record_multiple_databases.md
+++ b/guides/source/active_record_multiple_databases.md
@@ -32,6 +32,7 @@ The following features are not (yet) supported:
 * Sharding
 * Joining across clusters
 * Load balancing replicas
+* Dumping schema caches for multiple databases
 
 ## Setting up your application
 
@@ -121,6 +122,12 @@ config.active_record.writing_role = :default
 config.active_record.reading_role = :readonly
 ```
 
+It's important to connect to your database in a single model and then inherit from that model
+for the tables rather than connect multiple individual models to the same database. Database
+clients have a limit to the number of open connections there can be and if you do this it will
+multiply the number of connections you have since Rails uses the model class name for the
+connection specification name.
+
 Now that we have the database.yml and the new model set up it's time to create the databases.
 Rails 6.0 ships with all the rails tasks you need to use multiple databases in Rails.
 
@@ -173,7 +180,7 @@ to primary based on the HTTP verb and whether there was a recent write.
 
 If the application is receiving a POST, PUT, DELETE, or PATCH request the application will
 automatically write to the primary. For the specified time after the write the application
-will read from the replica. For a GET or HEAD request the application will read from the
+will read from the primary. For a GET or HEAD request the application will read from the
 replica unless there was a recent write.
 
 To activate the automatic connection switching middleware, add or uncomment the following
@@ -253,17 +260,29 @@ for the 'nonexistent' role.)`
 
 ## Caveats
 
+### Sharding
+
 As noted at the top, Rails doesn't (yet) support sharding. We had to do a lot of work
 to support multiple databases for Rails 6.0. The lack of support for sharding isn't
 an oversight, but does require additional work that didn't make it in for 6.0. For now
 if you need sharding it may be advisable to continue using one of the many gems
 that supports this.
 
+### Load Balancing Replicas
+
 Rails also doesn't support automatic load balancing of replicas. This is very
 dependent on your infrastructure. We may implement basic, primitive load balancing
 in the future, but for an application at scale this should be something your application
 handles outside of Rails.
 
-Lastly, you cannot join across databases. Rails 6.1 will support using `has_many`
+### Joining Across Databases
+
+Applications cannot join across databases. Rails 6.1 will support using `has_many`
 relationships and creating 2 queries instead of joining, but Rails 6.0 will require
 you to split the joins into 2 selects manually.
+
+### Schema Cache
+
+If you use a schema cache and multiple databases you'll need to write an initializer
+that loads the schema cache from your app. This wasn't an issue we could resolve in
+time for Rails 6.0 but hope to have it in a future version soon.
diff --git a/guides/source/active_support_core_extensions.md b/guides/source/active_support_core_extensions.md
index 21901a7158..8cb49ca6ae 100644
--- a/guides/source/active_support_core_extensions.md
+++ b/guides/source/active_support_core_extensions.md
@@ -3416,56 +3416,56 @@ NOTE: Defined in `active_support/core_ext/date_and_time/calculations.rb`.
 
 #### `prev_day`, `next_day`
 
-In Ruby 1.9 `prev_day` and `next_day` return the date in the last or next day:
+`prev_day` and `next_day` return the time in the last or next day:
 
 ```ruby
-d = Date.new(2010, 5, 8) # => Sat, 08 May 2010
-d.prev_day               # => Fri, 07 May 2010
-d.next_day               # => Sun, 09 May 2010
+t = Time.new(2010, 5, 8) # => 2010-05-08 00:00:00 +0900
+t.prev_day               # => 2010-05-07 00:00:00 +0900
+t.next_day               # => 2010-05-09 00:00:00 +0900
 ```
 
-NOTE: Defined in `active_support/core_ext/date_and_time/calculations.rb`.
+NOTE: Defined in `active_support/core_ext/time/calculations.rb`.
 
 #### `prev_month`, `next_month`
 
-In Ruby 1.9 `prev_month` and `next_month` return the date with the same day in the last or next month:
+`prev_month` and `next_month` return the time with the same day in the last or next month:
 
 ```ruby
-d = Date.new(2010, 5, 8) # => Sat, 08 May 2010
-d.prev_month             # => Thu, 08 Apr 2010
-d.next_month             # => Tue, 08 Jun 2010
+t = Time.new(2010, 5, 8) # => 2010-05-08 00:00:00 +0900
+t.prev_month             # => 2010-04-08 00:00:00 +0900
+t.next_month             # => 2010-06-08 00:00:00 +0900
 ```
 
 If such a day does not exist, the last day of the corresponding month is returned:
 
 ```ruby
-Date.new(2000, 5, 31).prev_month # => Sun, 30 Apr 2000
-Date.new(2000, 3, 31).prev_month # => Tue, 29 Feb 2000
-Date.new(2000, 5, 31).next_month # => Fri, 30 Jun 2000
-Date.new(2000, 1, 31).next_month # => Tue, 29 Feb 2000
+Time.new(2000, 5, 31).prev_month # => 2000-04-30 00:00:00 +0900
+Time.new(2000, 3, 31).prev_month # => 2000-02-29 00:00:00 +0900
+Time.new(2000, 5, 31).next_month # => 2000-06-30 00:00:00 +0900
+Time.new(2000, 1, 31).next_month # => 2000-02-29 00:00:00 +0900
 ```
 
-NOTE: Defined in `active_support/core_ext/date_and_time/calculations.rb`.
+NOTE: Defined in `active_support/core_ext/time/calculations.rb`.
 
 #### `prev_year`, `next_year`
 
-In Ruby 1.9 `prev_year` and `next_year` return a date with the same day/month in the last or next year:
+`prev_year` and `next_year` return a time with the same day/month in the last or next year:
 
 ```ruby
-d = Date.new(2010, 5, 8) # => Sat, 08 May 2010
-d.prev_year              # => Fri, 08 May 2009
-d.next_year              # => Sun, 08 May 2011
+t = Time.new(2010, 5, 8) # => 2010-05-08 00:00:00 +0900
+t.prev_year              # => 2009-05-08 00:00:00 +0900
+t.next_year              # => 2011-05-08 00:00:00 +0900
 ```
 
 If date is the 29th of February of a leap year, you obtain the 28th:
 
 ```ruby
-d = Date.new(2000, 2, 29) # => Tue, 29 Feb 2000
-d.prev_year               # => Sun, 28 Feb 1999
-d.next_year               # => Wed, 28 Feb 2001
+t = Time.new(2000, 2, 29) # => 2000-02-29 00:00:00 +0900
+t.prev_year               # => 1999-02-28 00:00:00 +0900
+t.next_year               # => 2001-02-28 00:00:00 +0900
 ```
 
-NOTE: Defined in `active_support/core_ext/date_and_time/calculations.rb`.
+NOTE: Defined in `active_support/core_ext/time/calculations.rb`.
 
 #### `prev_quarter`, `next_quarter`
 
diff --git a/guides/source/configuring.md b/guides/source/configuring.md
index 4651290674..e53e8b4e92 100644
--- a/guides/source/configuring.md
+++ b/guides/source/configuring.md
@@ -553,6 +553,10 @@ Defaults to `'signed cookie'`.
 
   Any exceptions that are not configured will be mapped to 500 Internal Server Error.
 
+* `config.action_dispatch.return_only_media_type_on_content_type` change the
+  return value of `ActionDispatch::Response#content_type` to the Content-Type
+  header without modification. Defaults to `false`.
+
 * `ActionDispatch::Callbacks.before` takes a block of code to run before the request.
 
 * `ActionDispatch::Callbacks.after` takes a block of code to run after the request.
@@ -835,10 +839,10 @@ You can find more detailed configuration options in the
    config.active_storage.paths[:ffprobe] = '/usr/local/bin/ffprobe'
    ```
 
-* `config.active_storage.variable_content_types` accepts an array of strings indicating the content types that Active Storage can transform through ImageMagick. The default is `%w(image/png image/gif image/jpg image/jpeg image/pjpeg image/tiff image/vnd.adobe.photoshop image/vnd.microsoft.icon)`.
+* `config.active_storage.variable_content_types` accepts an array of strings indicating the content types that Active Storage can transform through ImageMagick. The default is `%w(image/png image/gif image/jpg image/jpeg image/pjpeg image/tiff image/bmp image/vnd.adobe.photoshop image/vnd.microsoft.icon)`.
 
 * `config.active_storage.content_types_to_serve_as_binary` accepts an array of strings indicating the content types that Active Storage will always serve as an attachment, rather than inline. The default is `%w(text/html
-text/javascript image/svg+xml application/postscript application/x-shockwave-flash text/xml application/xml application/xhtml+xml)`.
+text/javascript image/svg+xml application/postscript application/x-shockwave-flash text/xml application/xml application/xhtml+xml application/mathml+xml text/cache-manifest)`.
 
 * `config.active_storage.queues.analysis` accepts a symbol indicating the Active Job queue to use for analysis jobs. When this option is `nil`, analysis jobs are sent to the default Active Job queue (see `config.active_job.default_queue_name`).
 
@@ -908,6 +912,7 @@ text/javascript image/svg+xml application/postscript application/x-shockwave-fla
 - `config.autoloader`: `:zeitwerk`
 - `config.action_view.default_enforce_utf8`: `false`
 - `config.action_dispatch.use_cookies_with_metadata`: `true`
+- `config.action_dispatch.return_only_media_type_on_content_type`: `false`
 - `config.action_mailer.delivery_job`: `"ActionMailer::MailDeliveryJob"`
 - `config.active_job.return_false_on_aborted_enqueue`: `true`
 - `config.active_storage.queues.analysis`: `:active_storage_analysis`
@@ -1536,7 +1541,7 @@ Disallow: /
 ```
 
 To block just specific pages, it's necessary to use a more complex syntax. Learn
-it on the [official documentation](http://www.robotstxt.org/robotstxt.html).
+it on the [official documentation](https://www.robotstxt.org/robotstxt.html).
 
 Evented File System Monitor
 ---------------------------
diff --git a/guides/source/contributing_to_ruby_on_rails.md b/guides/source/contributing_to_ruby_on_rails.md
index d3706a4dbf..9c28ff6a9c 100644
--- a/guides/source/contributing_to_ruby_on_rails.md
+++ b/guides/source/contributing_to_ruby_on_rails.md
@@ -139,7 +139,7 @@ changes to the master branch.
 
 When working with documentation, please take into account the [API Documentation Guidelines](api_documentation_guidelines.html) and the [Ruby on Rails Guides Guidelines](ruby_on_rails_guides_guidelines.html).
 
-NOTE: To help our CI servers you should add [ci skip] to your documentation commit message to skip build on that commit. Please remember to use it for commits containing only documentation changes.
+NOTE: For documentation changes, your commit message should include [ci skip]. This will skip running the test suite, helping us to cut down on our server costs. Keep in mind that you should only skip CI when your change touches documentation exclusively.
 
 Translating Rails Guides
 ------------------------
diff --git a/guides/source/getting_started.md b/guides/source/getting_started.md
index 64f4a3b6b3..ce45dbb2a7 100644
--- a/guides/source/getting_started.md
+++ b/guides/source/getting_started.md
@@ -28,7 +28,7 @@ curve diving straight into Rails. There are several curated lists of online reso
 for learning Ruby:
 
 * [Official Ruby Programming Language website](https://www.ruby-lang.org/en/documentation/)
-* [List of Free Programming Books](https://github.com/vhf/free-programming-books/blob/master/free-programming-books.md#ruby)
+* [List of Free Programming Books](https://github.com/EbookFoundation/free-programming-books/blob/master/free-programming-books.md#ruby)
 
 Be aware that some resources, while still excellent, cover versions of Ruby as old as
 1.6, and commonly 1.8, and will not include some syntax that you will see in day-to-day
diff --git a/guides/source/initialization.md b/guides/source/initialization.md
index c41eae18cf..556c85cc0f 100644
--- a/guides/source/initialization.md
+++ b/guides/source/initialization.md
@@ -108,6 +108,8 @@ A standard Rails application depends on several gems, specifically:
 * activerecord
 * activestorage
 * activesupport
+* actionmailbox
+* actiontext
 * arel
 * builder
 * bundler
@@ -160,8 +162,8 @@ namespace and executes the command if found.
 If Rails doesn't recognize the command, it hands the reins over to Rake
 to run a task of the same name.
 
-As shown, `Rails::Command` displays the help output automatically if the `args`
-are empty.
+As shown, `Rails::Command` displays the help output automatically if the `namespace`
+is empty.
 
 ```ruby
 module Rails::Command
@@ -289,7 +291,7 @@ def default_options
     environment:        (ENV["RAILS_ENV"] || ENV["RACK_ENV"] || "development").dup,
     daemonize:          false,
     caching:            nil,
-    pid:                Options::DEFAULT_PID_PATH,
+    pid:                ENV.fetch("PIDFILE", Options::DEFAULT_PIDFILE).dup,
     restart_cmd:        restart_command)
 end
 ```
@@ -538,6 +540,8 @@ require "rails"
   action_mailer/railtie
   active_job/railtie
   action_cable/engine
+  action_mailbox/engine
+  action_text/engine
   rails/test_unit/railtie
   sprockets/railtie
 ).each do |railtie|
diff --git a/guides/source/security.md b/guides/source/security.md
index 22c122d4b9..5bb7a51524 100644
--- a/guides/source/security.md
+++ b/guides/source/security.md
@@ -1211,4 +1211,4 @@ The security landscape shifts and it is important to keep up to date, because mi
 * 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).
+* A [good security blog](https://www.owasp.org) including the [Cross-Site scripting Cheat Sheet](https://github.com/OWASP/CheatSheetSeries/blob/master/cheatsheets/Cross_Site_Scripting_Prevention_Cheat_Sheet.md).
diff --git a/guides/source/upgrading_ruby_on_rails.md b/guides/source/upgrading_ruby_on_rails.md
index 54f014293d..4192063e9b 100644
--- a/guides/source/upgrading_ruby_on_rails.md
+++ b/guides/source/upgrading_ruby_on_rails.md
@@ -270,6 +270,16 @@ In that case, `app/models/concerns` is assumed to be a root directory (because i
 
 The `Concerns::` namespace worked with the classic autoloader as a side-effect of the implementation, but it was not really an intended behavior. An application using `Concerns::` needs to rename those classes and modules to be able to run in `zeitwerk` mode.
 
+#### Having `app` in the autoload paths
+
+Some projects want something like `app/api/base.rb` to define `API::Base`, and add `app` to the autoload paths to accomplish that in `classic` mode. Since Rails adds all subdirectories of `app` to the autoload paths automatically, we have another situation in which there are nested root directories, so that setup no longer works. Similar principle we explained above with `concerns`.
+
+If you want to keep that structure, you'll need to delete the subdirectory from the autoload paths in an initializer:
+
+```ruby
+ActiveSupport::Dependencies.autoload_paths.delete("#{Rails.root}/app/api")
+```
+
 #### Autoloaded Constants and Explicit Namespaces
 
 If a namespace is defined in a file, as `Hotel` is here:
@@ -391,6 +401,12 @@ To fix this, just remove the wildcards:
 config.autoload_paths << "#{config.root}/lib"
 ```
 
+#### Eager loading and autoloading are consistent
+
+In `classic` mode, if `app/models/foo.rb` defines `Bar`, you won't be able to autoload that file, but eager loading will work because it loads files recursively blindly. This can be a source of errors if you test things first eager loading, execution may fail later autoloading.
+
+In `zeitwerk` mode both loading modes are consistent, they fail and err in the same files.
+
 #### How to Use the Classic Autoloader in Rails 6
 
 Applications can load Rails 6 defaults and still use the classic autoloader by setting `config.autoloader` this way: