1 files changed, 21 insertions, 19 deletions
diff --git a/guides/source/active_record_migrations.md b/guides/source/active_record_migrations.md
index f914122242..f8f36bf600 100644
--- a/guides/source/active_record_migrations.md
+++ b/guides/source/active_record_migrations.md
@@ -21,7 +21,7 @@ Migration Overview
 ------------------
 
 Migrations are a convenient way to
-[alter your database schema over time](http://en.wikipedia.org/wiki/Schema_migration)
+[alter your database schema over time](https://en.wikipedia.org/wiki/Schema_migration)
 in a consistent and easy way. They use a Ruby DSL so that you don't have to
 write SQL by hand, allowing your schema and changes to be database independent.
 
@@ -229,7 +229,7 @@ As always, what has been generated for you is just a starting point. You can add
 or remove from it as you see fit by editing the
 `db/migrate/YYYYMMDDHHMMSS_add_details_to_products.rb` file.
 
-Also, the generator accepts column type as `references`(also available as
+Also, the generator accepts column type as `references` (also available as
 `belongs_to`). For instance:
 
 ```bash
@@ -241,7 +241,7 @@ generates
 ```ruby
 class AddUserRefToProducts < ActiveRecord::Migration[5.0]
   def change
-    add_reference :products, :user, index: true, foreign_key: true
+    add_reference :products, :user, foreign_key: true
   end
 end
 ```
@@ -313,7 +313,7 @@ will produce a migration that looks like this
 class AddDetailsToProducts < ActiveRecord::Migration[5.0]
   def change
     add_column :products, :price, :decimal, precision: 5, scale: 2
-    add_reference :products, :supplier, polymorphic: true, index: true
+    add_reference :products, :supplier, polymorphic: true
   end
 end
 ```
@@ -467,6 +467,8 @@ the first time (i.e. on the date the migration is applied).
 Some adapters may support additional options; see the adapter specific API docs
 for further information.
 
+NOTE: `null` and `default` cannot be specified via command line.
+
 ### Foreign Keys
 
 While it's not required you might want to add foreign key constraints to
@@ -956,10 +958,10 @@ ActiveRecord::Schema.define(version: 20080906171750) do
 
   create_table "products", force: true do |t|
     t.string   "name"
-    t.text "description"
+    t.text     "description"
     t.datetime "created_at"
     t.datetime "updated_at"
-    t.string "part_number"
+    t.string   "part_number"
   end
 end
 ```
@@ -970,11 +972,11 @@ on. Because this is database-independent, it could be loaded into any database
 that Active Record supports. This could be very useful if you were to
 distribute an application that is able to run against multiple databases.
 
-There is however a trade-off: `db/schema.rb` cannot express database specific
-items such as triggers, stored procedures or check constraints. While in a
-migration you can execute custom SQL statements, the schema dumper cannot
-reconstitute those statements from the database. If you are using features like
-this, then you should set the schema format to `:sql`.
+NOTE: `db/schema.rb` cannot express database specific items such as triggers,
+sequences, stored procedures or check constraints, etc. Please note that while
+custom SQL statements can be run in migrations, these statements cannot be reconstituted
+by the schema dumper. If you are using features like this, then you
+should set the schema format to `:sql`.
 
 Instead of using Active Record's schema dumper, the database's structure will
 be dumped using a tool specific to the database (via the `db:structure:dump`
@@ -1018,10 +1020,10 @@ such features, the `execute` method can be used to execute arbitrary SQL.
 Migrations and Seed Data
 ------------------------
 
-The main purpose of Rails' migration feature is to issue commands that modify the 
-schema using a consistent process. Migrations can also be used 
-to add or modify data. This is useful in an existing database that can't be destroyed 
-and recreated, such as a production database. 
+The main purpose of Rails' migration feature is to issue commands that modify the
+schema using a consistent process. Migrations can also be used
+to add or modify data. This is useful in an existing database that can't be destroyed
+and recreated, such as a production database.
 
 ```ruby
 class AddInitialProducts < ActiveRecord::Migration[5.0]
@@ -1037,10 +1039,10 @@ class AddInitialProducts < ActiveRecord::Migration[5.0]
 end
 ```
 
-To add initial data after a database is created, Rails has a built-in 
-'seeds' feature that makes the process quick and easy. This is especially 
-useful when reloading the database frequently in development and test environments. 
-It's easy to get started with this feature: just fill up `db/seeds.rb` with some 
+To add initial data after a database is created, Rails has a built-in
+'seeds' feature that makes the process quick and easy. This is especially
+useful when reloading the database frequently in development and test environments.
+It's easy to get started with this feature: just fill up `db/seeds.rb` with some
 Ruby code, and run `rails db:seed`:
 
 ```ruby