Validate multiple contexts on `valid?` and `invalid?` at once.

Example:

```ruby
class Person
  include ActiveModel::Validations

  attr_reader :name, :title
  validates_presence_of :name, on: :create
  validates_presence_of :title, on: :update
end

person = Person.new
person.valid?([:create, :update])    # => true
person.errors.messages               # => {:name=>["can't be blank"], :title=>["can't be blank"]}
```

1 files changed, 18 insertions, 0 deletions

diff --git a/activemodel/CHANGELOG.md b/activemodel/CHANGELOG.md
index 54fe5794e1..d7e64b8bf0 100644
--- a/activemodel/CHANGELOG.md
+++ b/activemodel/CHANGELOG.md
@@ -1,3 +1,21 @@
+*   Validate multiple contexts on `valid?` and `invalid?` at once.
+
+    Example:
+    
+        class Person
+          include ActiveModel::Validations
+    
+          attr_reader :name, :title
+          validates_presence_of :name, on: :create
+          validates_presence_of :title, on: :update
+        end
+    
+        person = Person.new
+        person.valid?([:create, :update])    # => true
+        person.errors.messages               # => {:name=>["can't be blank"], :title=>["can't be blank"]}
+
+    *Dmitry Polushkin*
+
 *   Add case_sensitive option for confirmation validator in models.
 
     *Akshat Sharma*