i3-sensible-pager man page
i3-sensible-pager — launches $PAGER with fallbacks
i3-sensible-pager is used by i3-nagbar(1) when you click on the view button.
It tries to start one of the following (in that order):
Please don’t complain about the order: If the user has any preference, they will have $PAGER set.
Michael Stapelberg and contributors