回答:
set-goal-column
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set-goal-column is an interactive compiled Lisp function in
`simple.el'.
It is bound to C-x C-n.
(set-goal-column ARG)
Set the current horizontal position as a goal for C-n and C-p.
Those commands will move to this position in the line moved to
rather than trying to keep the same horizontal position.
With a non-nil argument ARG, clears out the goal column
so that C-n and C-p resume vertical motion.
The goal column is stored in the variable `goal-column'.