8 files changed, 37 insertions, 13 deletions
diff --git a/guides/source/action_cable_overview.md b/guides/source/action_cable_overview.md
index 8f5c44849a..7a9ff96c44 100644
--- a/guides/source/action_cable_overview.md
+++ b/guides/source/action_cable_overview.md
@@ -671,6 +671,21 @@ To configure the URL, add a call to `action_cable_meta_tag` in your HTML layout
 HEAD. This uses a URL or path typically set via `config.action_cable.url` in the
 environment configuration files.
 
+### Worker Pool Configuration
+
+The worker pool is used to run connection callbacks and channel actions in
+isolation from the server's main thread. Action Cable allows the application
+to configure the number of simultaneously processed threads in the worker pool.
+
+```ruby
+config.action_cable.worker_pool_size = 4
+```
+
+Also, note that your server must provide at least the same number of database
+connections as you have workers. The default worker pool size is set to 4, so
+that means you have to make at least 4 database connections available.
+ You can change that in `config/database.yml` through the `pool` attribute.
+
 ### Other Configurations
 
 The other common option to configure is the log tags applied to the
@@ -688,11 +703,6 @@ config.action_cable.log_tags = [
 For a full list of all configuration options, see the
 `ActionCable::Server::Configuration` class.
 
-Also, note that your server must provide at least the same number of database
-connections as you have workers. The default worker pool size is set to 4, so
-that means you have to make at least that available. You can change that in
-`config/database.yml` through the `pool` attribute.
-
 ## Running Standalone Cable Servers
 
 ### In App
diff --git a/guides/source/action_controller_overview.md b/guides/source/action_controller_overview.md
index aa746e4731..d0d84251e4 100644
--- a/guides/source/action_controller_overview.md
+++ b/guides/source/action_controller_overview.md
@@ -212,7 +212,7 @@ class PeopleController < ActionController::Base
   end
 
   # This will pass with flying colors as long as there's a person key
-  # in the parameters, otherwise it'll raise a
+  # in the parameters, otherwise it'll raise an
   # ActionController::ParameterMissing exception, which will get
   # caught by ActionController::Base and turned into a 400 Bad
   # Request error.
diff --git a/guides/source/active_record_basics.md b/guides/source/active_record_basics.md
index b0d4bbd2c0..4cf4111bf0 100644
--- a/guides/source/active_record_basics.md
+++ b/guides/source/active_record_basics.md
@@ -45,7 +45,7 @@ relationships of the objects in an application can be easily stored and
 retrieved from a database without writing SQL statements directly and with less
 overall database access code.
 
-NOTE: If you are not familiar enough with relational database management systems (RDBMS) or structured query language (SQL), please go through [this tutorial](https://www.w3schools.com/sql/default.asp) (or [this one](http://www.sqlcourse.com/)) or study them by other means. Understanding how relational databases work is crucial to understanding Active Records and Rails in general.
+NOTE: Basic knowledge of relational database management systems (RDBMS) and structured query language (SQL) is helpful in order to fully understand Active Record. Please refer to [this tutorial](https://www.w3schools.com/sql/default.asp) (or [this one](http://www.sqlcourse.com/)) or study them by other means if you would like to learn more.
 
 ### Active Record as an ORM Framework
 
diff --git a/guides/source/active_record_callbacks.md b/guides/source/active_record_callbacks.md
index ebdee446f9..4568b467ef 100644
--- a/guides/source/active_record_callbacks.md
+++ b/guides/source/active_record_callbacks.md
@@ -310,7 +310,7 @@ end
 
 ### Using `:if` and `:unless` with a `Proc`
 
-Finally, it is possible to associate `:if` and `:unless` with a `Proc` object. This option is best suited when writing short validation methods, usually one-liners:
+It is possible to associate `:if` and `:unless` with a `Proc` object. This option is best suited when writing short validation methods, usually one-liners:
 
 ```ruby
 class Order < ApplicationRecord
@@ -338,6 +338,20 @@ class Comment < ApplicationRecord
 end
 ```
 
+### Combining Callback Conditions
+
+When multiple conditions define whether or not a callback should happen, an `Array` can be used. Moreover, you can apply both `:if` and `:unless` to the same callback.
+
+```ruby
+class Comment < ApplicationRecord
+  after_create :send_email_to_author,
+    if: [Proc.new { |c| c.user.allow_send_email? }, :author_wants_emails?],
+    unless: Proc.new { |c| c.article.ignore_comments? }
+end
+```
+
+The callback only runs when all the `:if` conditions and none of the `:unless` conditions are evaluated to `true`.
+
 Callback Classes
 ----------------
 
diff --git a/guides/source/active_record_migrations.md b/guides/source/active_record_migrations.md
index 905c76e5c1..2c1796c464 100644
--- a/guides/source/active_record_migrations.md
+++ b/guides/source/active_record_migrations.md
@@ -496,9 +496,6 @@ 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
diff --git a/guides/source/active_record_validations.md b/guides/source/active_record_validations.md
index 0fda7c5cfd..0c57802188 100644
--- a/guides/source/active_record_validations.md
+++ b/guides/source/active_record_validations.md
@@ -934,7 +934,7 @@ end
 
 ### Using a Proc with `:if` and `:unless`
 
-Finally, it's possible to associate `:if` and `:unless` with a `Proc` object
+It is possible to associate `:if` and `:unless` with a `Proc` object
 which will be called. Using a `Proc` object gives you the ability to write an
 inline condition instead of a separate method. This option is best suited for
 one-liners.
diff --git a/guides/source/asset_pipeline.md b/guides/source/asset_pipeline.md
index e7faa5c330..9f8edea598 100644
--- a/guides/source/asset_pipeline.md
+++ b/guides/source/asset_pipeline.md
@@ -745,7 +745,7 @@ mapping requests back to Sprockets. A typical manifest file looks like:
 The default location for the manifest is the root of the location specified in
 `config.assets.prefix` ('/assets' by default).
 
-NOTE: If there are missing precompiled files in production you will get an
+NOTE: If there are missing precompiled files in production you will get a
 `Sprockets::Helpers::RailsHelper::AssetPaths::AssetNotPrecompiledError`
 exception indicating the name of the missing file(s).
 
diff --git a/guides/source/configuring.md b/guides/source/configuring.md
index e7129dd274..ad82614a0d 100644
--- a/guides/source/configuring.md
+++ b/guides/source/configuring.md
@@ -791,6 +791,9 @@ main application.
 You can set this as nil to not mount Action Cable as part of your
 normal Rails server.
 
+You can find more detailed configuration options in the
+[Action Cable Overview](action_cable_overview.html#configuration).
+
 
 ### Configuring Active Storage