Kind `10017` indicates the user's preferred relays for proxy downloads. Such services save the user's bandwidth by utilizing a single connection to a proxy relay which reaches out to all of the other relays.
Kind `10018` indicates the user's preferred relays for broadcasting relays. Such services improve the user's privacy by utilizing a broadcasting relay to distribute an event to all of the appropriate relays without requiring the user to connect with each of those relays.
Both events MUST include a list of `relay` URLs in private tags. Private tags are JSON Stringified, NIP-44-encrypted to the signer's keys and placed inside the `.content` of the event.