These are added as "surrogate keys" in the response. It allows you to "tag" multiple responses with a tag and then purge by that tag. So for example any view tagged with "simple" can be purged all together by telling fastly to purge the "simple" tag. It also allows you to use the paramters to the function with string formatting so you can do things like ``"simple~{project_name!n}"`` which will get interpolated out at call time for something like ``project_json(None, None, "foo")``, ``"simple~foo"``. The ``!n`` is an extension to string formatting I wrote that "normalizes" the name using the normalize function that lower cases and such.

I'll write this all up in a docstring though.