Bip39 Standard. Keep in mind, there isn't a these thing as a “Improper” passphrase. Just about every diverse passphrase you enter can be a fully new wallet. Watch out when recovering your seed using a passphrase. BIP39 specifies a list of 2048 words from which the mnemonic phrase is selected. https://bookmarkinglog.com/story18777279/bip39-passphrase-https-linktr-ee-bip39-the-2-minute-rule-for-bip39-word-list