http://i3xi5qxvbrngh3g6o7czwjfxwjzigook7zxzjmgwg5b7xnjcn5hzciad.onion/proposals/273-exit-relay-pinning.html
Instead of having a web server *tell* Tor Browser about pinned exit
relays, we could have Tor Browser *ask* the web server, e.g., by
making it fetch a predefined URL, similar to robots.txt. We believe
that this would involve too much overhead because only a tiny
fraction of sites that Tor users visit will have an ERP policy.