# File lib/buildr/core/filter.rb, line 316
      def transform(content, path = nil)
        type = Regexp === mapper_type ? :regexp : mapper_type
        raise ArgumentError, "Invalid mapper type: #{type.inspect}" unless respond_to?("#{type}_transform", true)
        self.__send__("#{type}_transform", content, path) { |key| config[key] || config[key.to_s.to_sym] }
      end