Bip39 Ian Coleman. Firstly you need to keep it Independently out of your seed. Getting your seed along with your passphrase in a similar locale defeats the goal of using a passphrase to begin with. BIP39 specifies a list of 2048 words from which the mnemonic phrase is decided on. https://bookmarklethq.com/story19040791/bip39-wallet-https-linktr-ee-bip39-bip39-wallet-fundamentals-explained