The idea of an xpub originates from BIP32, the place it denotes an prolonged public key, from which a number of little one keys will be derived.
On the time of BIP32, there was actually just one handle kind generally used, pay-to-pubkey-hash (P2PKH). Thus, BIP32 have been generally understood to suggest a sequence of derived P2PKH addresses.
After segwit, when different handle sorts got here in widespread use, like P2SH-P2WPKH and P2WPKH, individuals wanted a solution to convey “a BIP32 prolonged public key, however the derived addresses are P2SH-P2WPKH”. This turned the ypub scheme outlined in BIP49 for P2SH-P2WPKH, and later the zpub scheme in BIP84 for P2WPKH. They comprise the very same info as a BIP32 prolonged public key, however with a unique prefix to indicate the corresponding handle kind. Varied different variants have been outlined and adopted by some software program, e.g. Zpub for P2WSH, however not standardized via the BIP course of so far as I do know.
Different software program by no means adopted ypub/zpub/Zpub/…, because the persevering with want for brand new prefixes doesn’t scale properly, and the notion of making an attempt to pack all handle derivation info right into a single key string additionally simply would not work for extra complicated constructions like multisig. For instance, within the newer output descriptors (BIP380) commonplace, xpub is at all times used, however one would use wpkh(xpub...) to point a P2WPKH handle kind.
So far as I do know, there isn’t a *pub-like commonplace for P2TR but, and for my part there shouldn’t be. It’s a lot clearer to convey handle kind info outdoors of key strings.
Disclaimer: I am the writer of BIP32, and co-author of BIP380.
