This tag freezes a state with multiple httpd backends to choose from, (to evaluate the future backend to use). The result of this testing was to switch to 'twisted' after this point. Keeping all backends source code would (be sort of confusing and) also mean all dependencies need to be installed (or implement a multitude of exceptions for the testing/building suite). We rather clean things up from here on, and mark this should we ever want to review the other backends. Backends: cherrypy, tornado, twisted, waitress, wsgiref.