The hardest problem in computer science...

[Alain Ketterlin]

Steve D'Aprano <steve+python at pearwood.info> writes:

[...]
>     Fiction
>     ├─ Fantasy
>     │  ├─ Terry Pratchett
>     │  │  ├─ Discworld
>     │  │  │  ├─ Wyrd Sisters
>     │  │  │  └─ Carpe Jugulum
>     │  │  └─ Dodger
>     │  └─ JK Rowling
[...]
> what do we call the vertical and horizontal line elements?

Box-drawing characters. At least that's how Unicode calls them. Even if
you don't draw boxes...

https://en.wikipedia.org/wiki/Box-drawing_character

-- Alain.