to_xml

# File activesupport/lib/active_support/core_ext/hash/conversions.rb, line 99
        def to_xml(options = {})
          require 'builder' unless defined?(Builder)

          options = options.dup
          options[:indent] ||= 2
          options.reverse_merge!({ :builder => Builder::XmlMarkup.new(:indent => options[:indent]),
                                   :root => "hash" })
          options[:builder].instruct! unless options.delete(:skip_instruct)
          root = rename_key(options[:root].to_s, options)

          options[:builder].__send__(:method_missing, root) do
            each do |key, value|
              case value
                when ::Hash
                  value.to_xml(options.merge({ :root => key, :skip_instruct => true }))
                when ::Array
                  value.to_xml(options.merge({ :root => key, :children => key.to_s.singularize, :skip_instruct => true}))
                when ::Method, ::Proc
                  # If the Method or Proc takes two arguments, then
                  # pass the suggested child element name.  This is
                  # used if the Method or Proc will be operating over
                  # multiple records and needs to create an containing
                  # element that will contain the objects being
                  # serialized.
                  if 1 == value.arity
                    value.call(options.merge({ :root => key, :skip_instruct => true }))
                  else
                    value.call(options.merge({ :root => key, :skip_instruct => true }), key.to_s.singularize)
                  end
                else
                  if value.respond_to?(:to_xml)
                    value.to_xml(options.merge({ :root => key, :skip_instruct => true }))
                  else
                    type_name = XML_TYPE_NAMES[value.class.name]

                    key = rename_key(key.to_s, options)

                    attributes = options[:skip_types] || value.nil? || type_name.nil? ? { } : { :type => type_name }
                    if value.nil?
                      attributes[:nil] = true
                    end

                    options[:builder].tag!(key,
                      XML_FORMATTING[type_name] ? XML_FORMATTING[type_name].call(value) : value,
                      attributes
                    )
                  end
              end
            end
            
            yield options[:builder] if block_given?
          end

        end