PROMPT_DIRTRIM
I am not very willing to add a feature that can be easily achieved with a script. If you really want this as a built-in feature of the shell, please reopen this feature request at GitHub <https://github.com/magicant/yash/issues> and elaborate why this should be built-in.
Its shown the last $PROMPT_DIRTRIM directories of $PWD. Cosmetic, bash's PROMPT_DIRTRIM = tcsh's ellipsis = zsh's %Nd, its simple and useful in prompt, easy to implement.