ActiveRecord::Errors#to_xml (See related posts)

class ActiveRecord::Errors
  def to_xml(options = {})
    options[:indent] ||= 2
    options.reverse_merge!({ :builder =>
      Builder::XmlMarkup.new(:indent =>
        options[:indent]), :root => "errors" })
    options[:builder].instruct! unless options.delete(:skip_instruct)

    options[:builder].__send__(options[:root].to_s.dasherize) do |xml|
      @errors.each do |key, value|
        xml.__send__(key.to_s.dasherize) do |xm|
          for message in value
            xm.message(message)
          end
        end
      end
    end

  end
end