NIP-05 lookup
With the Nip05Helper class you can easily request (with a simple http GET request) a given "nip05" internet identifier. This identifier is often part of the event kind 0 (user metadata) related to a pubkey. You can fetch this metadata with the Profile class in the library. If available, a JSON document object is returned.
Here is a simple example using the Nip05Helper class.
php
// The internet identifier
$identifier = 'sebastian@sebastix.dev';
$nip05 = new Nip05Helper();
// Get the public key
$pubkey = $nip05->getPublicKey($identifier);
// Get the relays
$relays = $nip05->getRelays($identifier);