    # File lib/active_support/core_ext/string/multibyte.rb, line 67
              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