This section describes how to change the position of an existing marker. When you do this, be sure you know whether the marker is used outside of your program, and, if so, what effects will result from moving it—otherwise, confusing things may happen in other parts of Emacs.
This function moves marker to position in buffer. If buffer is not provided, it defaults to the current buffer.
If position is less than 1,
set-markermoves marker to the beginning of the buffer. If position is greater than the size of the buffer (see Point),
set-markermoves marker to the end of the buffer. If position is
nilor a marker that points nowhere, then marker is set to point nowhere.
The value returned is marker.(setq m (point-marker)) ⇒ #<marker at 4714 in markers.texi> (set-marker m 55) ⇒ #<marker at 55 in markers.texi> (setq b (get-buffer "foo")) ⇒ #<buffer foo> (set-marker m 0 b) ⇒ #<marker at 1 in foo>