- Instead of invariably using ``webob.Request`` as the "request
  factory" (e.g. in the ``Router`` class) and ``webob.Response`` and
  the "response factory" (e.g. in ``render_template_to_response``),
  allow both to be overridden via a ZCML utility hook.  See the "Using
  ZCML Hooks" chapter of the documentation for more information.