Bip39 Algorithm. From this stage forward the seed may be penned on paper or spoken about phone and this opened up new, Bodily means of backing up the seed (various paper copies in various places, strong copies on metallic plates with extra protection from fireplace/flood and so on.). The BIP39 https://emiliobpdtg.mysticwiki.com/1101273/the_anatomy_of_a_bip39_phrase_entropy_text_and_protection