ed was based on using the teletype – the “persistent display” was the paper itself
What I really love is that when the teletype has finished printing off his little diary, Rex can simply tear it off and walk away, keeping it in his pocket, put on his wall. It’s produced a little physical artifact for him to carry around.
Noticing a lot of similarities with vi! Happy to have had that tour, though I’m not sure I’ve encountered a system without vi or nano yet.
E: I have since discovered that the default mail program accepts ed commands as described here, such as p$ to print the last mail