diff --git a/activesupport/CHANGELOG b/activesupport/CHANGELOG
index 69c2c0166a4bf06a6191e9fc3194f00ef78fdb7a..80b4ad9776ae48eb67cc7fcb16874028bce2a63f 100644
--- a/activesupport/CHANGELOG
+++ b/activesupport/CHANGELOG
@@ -1,5 +1,7 @@
 *SVN*
 
+* Document Object#blank?.  #6491 [Chris Mear]
+
 * Date, Time, and DateTime#to_json.  #8399 [wycats]
 
 * Simplify API of assert_difference by passing in an expression that is evaluated before and after the passed in block. See documenation for examples of new API. [Marcel Molina Jr.]
diff --git a/activesupport/lib/active_support/core_ext/blank.rb b/activesupport/lib/active_support/core_ext/blank.rb
index 80feaf5cc6c92c577402682cb44db0ba56052c9f..d2a940f5b98926703aef5cafda6fada5e308f659 100644
--- a/activesupport/lib/active_support/core_ext/blank.rb
+++ b/activesupport/lib/active_support/core_ext/blank.rb
@@ -1,6 +1,12 @@
-class Object 
-  # "", "   ", nil, [], and {} are blank
-  def blank? #:nodoc:
+class Object
+  # An object is blank if it's nil, empty, or a whitespace string.
+  # For example, "", "   ", nil, [], and {} are blank.
+  #
+  # This simplifies
+  #   if !address.nil? && !address.empty?
+  # to
+  #   if !address.blank?
+  def blank?
     if respond_to?(:empty?) && respond_to?(:strip)
       empty? or strip.empty?
     elsif respond_to?(:empty?)
@@ -47,4 +53,4 @@ class Numeric #:nodoc:
   def blank?
     false
   end
-end
\ No newline at end of file
+end