6 files changed, 66 insertions, 25 deletions
diff --git a/guides/source/action_mailer_basics.md b/guides/source/action_mailer_basics.md
index 2bc8fb1baf..37cbf3f53d 100644
--- a/guides/source/action_mailer_basics.md
+++ b/guides/source/action_mailer_basics.md
@@ -433,7 +433,6 @@ class UserMailer < ApplicationMailer
     # ...
   end
 end
-
 ```
 
 You can also consider using the [append_view_path](https://guides.rubyonrails.org/action_view_overview.html#view-paths) method.
diff --git a/guides/source/active_record_basics.md b/guides/source/active_record_basics.md
index d90ea2e26a..fad4c19827 100644
--- a/guides/source/active_record_basics.md
+++ b/guides/source/active_record_basics.md
@@ -115,7 +115,7 @@ to Active Record instances:
 * `created_at` - Automatically gets set to the current date and time when the
   record is first created.
 * `updated_at` - Automatically gets set to the current date and time whenever
-  the record is updated.
+  the record is created or updated.
 * `lock_version` - Adds [optimistic
   locking](http://api.rubyonrails.org/classes/ActiveRecord/Locking.html) to
   a model.
diff --git a/guides/source/active_record_migrations.md b/guides/source/active_record_migrations.md
index cfa444fda0..4d195988f8 100644
--- a/guides/source/active_record_migrations.md
+++ b/guides/source/active_record_migrations.md
@@ -491,6 +491,9 @@ NOTE: Active Record only supports single column foreign keys. `execute` and
 `structure.sql` are required to use composite foreign keys. See
 [Schema Dumping and You](#schema-dumping-and-you).
 
+NOTE: The SQLite3 adapter doesn't support `add_foreign_key` since SQLite supports
+only [a limited subset of ALTER TABLE](https://www.sqlite.org/lang_altertable.html).
+
 Removing a foreign key is easy as well:
 
 ```ruby
@@ -923,9 +926,10 @@ your database schema.
 
 It tends to be faster and less error prone to create a new instance of your
 application's database by loading the schema file via `rails db:schema:load`
-than it is to replay the entire migration history. Old migrations may fail to
-apply correctly if those migrations use changing external dependencies or rely
-on application code which evolves separately from your migrations.
+than it is to replay the entire migration history.
+[Old migrations](#old-migrations) may fail to apply correctly if those
+migrations use changing external dependencies or rely on application code which
+evolves separately from your migrations.
 
 Schema files are also useful if you want a quick look at what attributes an
 Active Record object has. This information is not in the model's code and is
@@ -1042,3 +1046,21 @@ end
 
 This is generally a much cleaner way to set up the database of a blank
 application.
+
+Old Migrations
+--------------
+
+The `db/schema.rb` or `db/structure.sql` is a snapshot of the current state of your
+database and is the authoritative source for rebuilding that database. This
+makes it possible to delete old migration files.
+
+When you delete migration files in the `db/migrate/` directory, any environment
+where `rails db:migrate` was run when those files still existed will hold a reference
+to the migration timestamp specific to them inside an internal Rails database
+table named `schema_migrations`. This table is used to keep track of whether
+migrations have been executed in a specific environment.
+
+If you run the `rails db:migrate:status` command, which displays the status
+(up or down) of each migration, you should see `********** NO FILE **********`
+displayed next to any deleted migration file which was once executed on a
+specific environment but can no longer be found in the `db/migrate/` directory.
diff --git a/guides/source/active_support_core_extensions.md b/guides/source/active_support_core_extensions.md
index dfd21915b0..f9fc7044ba 100644
--- a/guides/source/active_support_core_extensions.md
+++ b/guides/source/active_support_core_extensions.md
@@ -2156,6 +2156,19 @@ This method is an alias of `Array#<<`.
 
 NOTE: Defined in `active_support/core_ext/array/prepend_and_append.rb`.
 
+### Extracting
+
+The method `extract!` removes and returns the elements for which the block returns a true value.
+If no block is given, an Enumerator is returned instead.
+
+```ruby
+numbers = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]
+odd_numbers = numbers.extract! { |number| number.odd? } # => [1, 3, 5, 7, 9]
+numbers # => [0, 2, 4, 6, 8]
+```
+
+NOTE: Defined in `active_support/core_ext/array/extract.rb`.
+
 ### Options Extraction
 
 When the last argument in a method call is a hash, except perhaps for a `&block` argument, Ruby allows you to omit the brackets:
diff --git a/guides/source/development_dependencies_install.md b/guides/source/development_dependencies_install.md
index 057bcf2c1b..439797ddcb 100644
--- a/guides/source/development_dependencies_install.md
+++ b/guides/source/development_dependencies_install.md
@@ -350,57 +350,65 @@ prerequisite for installing this package manager is that
 On macOS, you can run:
 
 ```bash
-brew install yarn
+$ 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
+$ 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
+$ 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 wget https://dl.yarnpkg.com/rpm/yarn.repo -O /etc/yum.repos.d/yarn.repo
 
-sudo yum install yarn
+$ 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
+$ yarn install
 ```
 
-Extracting previews, tested in ActiveStorage's test suite requires third-party
+Extracting previews, tested in Active Storage's test suite requires third-party
 applications, FFmpeg for video and muPDF for PDFs, and on macOS also XQuartz
-and Poppler. Without these applications installed, ActiveStorage tests will
+and Poppler. Without these applications installed, Active Storage tests will
 raise errors.
 
 On macOS you can run:
 
 ```bash
-brew install ffmpeg
-brew cask install xquartz
-brew install mupdf-tools
-brew install poppler
+$ brew install ffmpeg
+$ brew cask install xquartz
+$ brew install mupdf-tools
+$ brew install poppler
 ```
 
 On Ubuntu, you can run:
 
 ```bash
-sudo apt-get update && install ffmpeg
-sudo apt-get update && install mupdf mupdf-tools
+$ sudo apt-get update
+$ sudo apt-get install ffmpeg
+$ sudo apt-get install mupdf mupdf-tools
 ```
 
 On Fedora or CentOS, just run:
 
 ```bash
-sudo yum install ffmpeg
-sudo yum install mupdf
+$ sudo yum install ffmpeg
+$ sudo yum install mupdf
+```
+
+FreeBSD users can just run:
+
+```bash
+# pkg install ffmpeg
+# pkg install mupdf
 ```
diff --git a/guides/source/testing.md b/guides/source/testing.md
index 01cda8e6e4..de93e1c653 100644
--- a/guides/source/testing.md
+++ b/guides/source/testing.md
@@ -1113,11 +1113,10 @@ end
 
 Now you can try running all the tests and they should pass.
 
-NOTE: If you followed the steps in the Basic Authentication section, you'll need to add the following to the `setup` block to get all the tests passing:
+NOTE: If you followed the steps in the Basic Authentication section, you'll need to add authorization to every request header to get all the tests passing:
 
 ```ruby
-request.headers['Authorization'] = ActionController::HttpAuthentication::Basic.
-  encode_credentials('dhh', 'secret')
+post articles_url, params: { article: { body: 'Rails is awesome!', title: 'Hello Rails' } }, headers: { Authorization: ActionController::HttpAuthentication::Basic.encode_credentials('dhh', 'secret') }
 ```
 
 ### Available Request Types for Functional Tests