Window Point - GNU Emacs Lisp Reference Manual

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27.18 Windows and Point

Each window has its own value of point (see Point), independent of the value of point in other windows displaying the same buffer. This makes it useful to have multiple windows showing one buffer.

The window point is established when a window is first created; it is initialized from the buffer's point, or from the window point of another window opened on the buffer if such a window exists.
Selecting a window sets the value of point in its buffer from the window's value of point. Conversely, deselecting a window sets the window's value of point from that of the buffer. Thus, when you switch between windows that display a given buffer, the point value for the selected window is in effect in the buffer, while the point values for the other windows are stored in those windows.
As long as the selected window displays the current buffer, the window's point and the buffer's point always move together; they remain equal.

As far as the user is concerned, point is where the cursor is, and when the user switches to another buffer, the cursor jumps to the position of point in that buffer.

— Function: window-point &optional window

This function returns the current position of point in window. For a nonselected window, this is the value point would have (in that window's buffer) if that window were selected. The default for window is the selected window.
When window is the selected window, the value returned is the value of point in that window's buffer. Strictly speaking, it would be more correct to return the “top-level” value of point, outside of any save-excursion forms. But that value is hard to find.

— Function: set-window-point window position

This function positions point in window at position position in window's buffer. It returns position.
If window is selected, this simply does goto-char in window's buffer.

— Variable: window-point-insertion-type

This variable specifies the marker insertion type (see Marker Insertion Types) of window-point. The default is nil, so window-point will stay behind text inserted there.