README.md in blind_index-2.0.2 vs README.md in blind_index-2.1.0

@@ -24,17 +24,17 @@
 
 ```ruby
 gem 'blind_index'
 ```
 
-## Getting Started
+## Prep
 
 Your model should already be set up with Lockbox or attr_encrypted. The examples are for a `User` model with `encrypts :email` or `attr_encrypted :email`. See the full examples for [Lockbox](https://ankane.org/securing-user-emails-lockbox) and [attr_encrypted](https://ankane.org/securing-user-emails-in-rails) if needed.
 
 Also, if you use attr_encrypted, [generate a key](#key-generation).
 
----
+## Getting Started
 
 Create a migration to add a column for the blind index
 
 ```ruby
 add_column :users, :email_bidx, :string
@@ -67,29 +67,51 @@
 
 ```ruby
 User.where(email: "[e-mail]")
 ```
 
+## Expressions
+
+You can apply expressions to attributes before indexing and searching. This gives you the the ability to perform case-insensitive searches and more.
+
+```ruby
+class User < ApplicationRecord
+  blind_index :email, expression: ->(v) { v.downcase }
+end
+```
+
 ## Validations
 
-To prevent duplicates, use:
+You can use blind indexes for uniqueness validations.
 
 ```ruby
 class User < ApplicationRecord
   validates :email, uniqueness: true
 end
 ```
 
-We also recommend adding a unique index to the blind index column through a database migration.
+We recommend adding a unique index to the blind index column through a database migration.
 
-## Expressions
+```ruby
+add_index :users, :email_bidx, unique: true
+```
 
-You can apply expressions to attributes before indexing and searching. This gives you the the ability to perform case-insensitive searches and more.
+For `allow_blank: true`, use:
 
 ```ruby
 class User < ApplicationRecord
+  blind_index :email, expression: ->(v) { v.presence }
+  validates :email, uniqueness: {allow_blank: true}
+end
+```
+
+For `case_sensitive: false`, use:
+
+```ruby
+class User < ApplicationRecord
   blind_index :email, expression: ->(v) { v.downcase }
+  validates :email, uniqueness: true # for best performance, leave out {case_sensitive: false}
 end
 ```
 
 ## Multiple Indexes
 
@@ -434,5 +456,7 @@
 git clone https://github.com/ankane/blind_index.git
 cd blind_index
 bundle install
 bundle exec rake test
 ```
+
+For security issues, send an email to the address on [this page](https://github.com/ankane).