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diff --git a/activesupport/lib/active_support/core_ext/string/multibyte.rb b/activesupport/lib/active_support/core_ext/string/multibyte.rb
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+++ b/activesupport/lib/active_support/core_ext/string/multibyte.rb
@@ -0,0 +1,81 @@
+# encoding: utf-8
+
+module ActiveSupport #:nodoc:
+  module CoreExtensions #:nodoc:
+    module String #:nodoc:
+      # Implements multibyte methods for easier access to multibyte characters in a String instance.
+      module Multibyte
+        unless '1.9'.respond_to?(:force_encoding)
+          # == Multibyte proxy
+          #
+          # +mb_chars+ is a multibyte safe proxy for string methods.
+          #
+          # In Ruby 1.8 and older it creates and returns an instance of the ActiveSupport::Multibyte::Chars class which
+          # encapsulates the original string. A Unicode safe version of all the String methods are defined on this proxy
+          # class. If the proxy class doesn't respond to a certain method, it's forwarded to the encapsuled string.
+          #
+          #   name = 'Claus Müller'
+          #   name.reverse  #=> "rell??M sualC"
+          #   name.length   #=> 13
+          #
+          #   name.mb_chars.reverse.to_s   #=> "rellüM sualC"
+          #   name.mb_chars.length         #=> 12
+          #
+          # In Ruby 1.9 and newer +mb_chars+ returns +self+ because String is (mostly) encoding aware. This means that
+          # it becomes easy to run one version of your code on multiple Ruby versions.
+          #
+          # == Method chaining
+          #
+          # All the methods on the Chars proxy which normally return a string will return a Chars object. This allows
+          # method chaining on the result of any of these methods.
+          #
+          #   name.mb_chars.reverse.length #=> 12
+          #
+          # == Interoperability and configuration
+          #
+          # The Chars object tries to be as interchangeable with String objects as possible: sorting and comparing between
+          # String and Char work like expected. The bang! methods change the internal string representation in the Chars
+          # object. Interoperability problems can be resolved easily with a +to_s+ call.
+          #
+          # For more information about the methods defined on the Chars proxy see ActiveSupport::Multibyte::Chars. For
+          # information about how to change the default Multibyte behaviour see ActiveSupport::Multibyte.
+          def mb_chars
+            if ActiveSupport::Multibyte.proxy_class.wants?(self)
+              ActiveSupport::Multibyte.proxy_class.new(self)
+            else
+              self
+            end
+          end
+          
+          # Returns true if the string has UTF-8 semantics (a String used for purely byte resources is unlikely to have
+          # them), returns false otherwise.
+          def is_utf8?
+            ActiveSupport::Multibyte::Chars.consumes?(self)
+          end
+
+          unless '1.8.7 and later'.respond_to?(:chars)
+            def chars
+              ActiveSupport::Deprecation.warn('String#chars has been deprecated in favor of String#mb_chars.', caller)
+              mb_chars
+            end
+          end
+        else
+          def mb_chars #:nodoc
+            self
+          end
+          
+          def is_utf8? #:nodoc
+            case encoding
+            when Encoding::UTF_8
+              valid_encoding?
+            when Encoding::ASCII_8BIT, Encoding::US_ASCII
+              dup.force_encoding(Encoding::UTF_8).valid_encoding?
+            else
+              false
+            end
+          end
+        end
+      end
+    end
+  end
+end