Base58chk-encoded extended keys are always 111 characters long. Amend wording of BIP accordingly.

-This results in a Base58-encoded string of up to 112 characters.
+This results in a Base58-encoded string of exactly 111 characters.

Version bytes: 0x0488b21e (“xpub”), 0x0488ade4 (“xprv”), 0x043587cf (“tpub”), 0x04358394 (“tprv”)

Largest “possible” key:
   kL = 0x0488b21effffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffffff (78 bytes)
   b58chk(kL) = xpubEPi3iGSX9RiyuXPTijevUmMctBDQs2TWCMgUd3qKp6qCgUc8RUsPdPBrRC6whFeWTg37DcmnJJiKFL73DH4sjdApJkXBD3vFcBP4xHq3fPY (111 chars)

Smallest “possible” key:
   kS = 0x043583940000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000 (78 bytes)
   b58chk(kS) = tprv8ZgxMBicQKsPcsbCVeqqF1KVdH7gwDJbxbzpCxDUsoXHdb6SnTPYxdwSAKDC6KKJzv7khnNWRAJQsRA8BBQyiSfYnRt6zuu4vZQGKjeW4YF (111 chars)

Author: mmgen

bip-0032.mediawiki

@@ -137,7 +137,7 @@ Extended public and private keys are serialized as follows:
 * 32 bytes: the chain code
 * 33 bytes: the public key or private key data (ser<sub>P</sub>(K) for public keys, 0x00 || ser<sub>256</sub>(k) for private keys)
 
-This 78 byte structure can be encoded like other Bitcoin data in Base58, by first adding 32 checksum bits (derived from the double SHA-256 checksum), and then converting to the Base58 representation. This results in a Base58-encoded string of up to 112 characters. Because of the choice of the version bytes, the Base58 representation will start with "xprv" or "xpub" on mainnet, "tprv" or "tpub" on testnet.
+This 78 byte structure can be encoded like other Bitcoin data in Base58, by first adding 32 checksum bits (derived from the double SHA-256 checksum), and then converting to the Base58 representation. This results in a Base58-encoded string of exactly 111 characters. Because of the choice of the version bytes, the Base58 representation will start with "xprv" or "xpub" on mainnet, "tprv" or "tpub" on testnet.
 
 Note that the fingerprint of the parent only serves as a fast way to detect parent and child nodes in software, and software must be willing to deal with collisions. Internally, the full 160-bit identifier could be used.