new (Rack::Utils::Context)

    # File lib/rack/utils.rb, line 130
          def initialize app_f, app_r
            raise 'running context not provided' unless app_f
            raise 'running context does not respond to #context' unless app_f.respond_to? :context
            raise 'application context not provided' unless app_r
            raise 'application context does not respond to #call' unless app_r.respond_to? :call
            @for = app_f
            @app = app_r
          end