C-x 4 is a prefix key for commands that select another window (splitting the window if there is only one) and select a buffer in that window. Different C-x 4 commands have different ways of finding the buffer to select.
switch-to-buffer-other-window
.
display-buffer
.
find-file-other-window
. See section Visiting Files.
dired-other-window
. See section Dired, the Directory Editor.
mail-other-window
; its same-window analogue is C-x m
(see section Sending Mail).
find-tag-other-window
, the multiple-window variant of M-.
(see section Tags Tables).
find-file-read-only-other-window
.
See section Visiting Files.
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