# File lib/sinatra/reloader.rb, line 291
      def add_filter(type, path = nil, options = {}, &block)
        source_location = block.respond_to?(:source_location) ?
          block.source_location.first : caller_files[1]
        result = super
        watch_element(source_location, "#{type}_filter""#{type}_filter", filters[type].last)
        result
      end