This function makes window the selected window and the window selected within its frame (see Basic Windows), and selects that frame. It also makes window’s buffer (see Buffers and Windows) current and sets that buffer’s value of point to the value of window-point (see Window Point) in window. window must be a live window. The return value is window.
By default, this function also moves window’s buffer to the front of the buffer list (see Buffer List) and makes window the most recently selected window. If the optional argument norecord is non-nil, these additional actions are omitted.
In addition, this function by default also tells the display engine to update the display of window when its frame gets redisplayed the next time. If norecord is non-nil, such updates are usually not performed. If, however, norecord equals the special symbol mark-for-redisplay, the additional actions mentioned above are omitted but window will be nevertheless updated.
Note that sometimes selecting a window is not enough to show it, or make its frame the top-most frame on display: you may also need to raise the frame or make sure input focus is directed to that frame. See Input Focus.
For historical reasons, Emacs does not run a separate hook whenever a window gets selected. Applications and internal routines often temporarily select a window to perform a few actions on it. They do that either to simplify coding—because many functions by default operate on the selected window when no window argument is specified—or because some functions did not (and still do not) take a window as argument and always operate(d) on the selected window instead. Running a hook every time a window gets selected for a short time and once more when the previously selected window gets restored is not useful.
However, when its norecord argument is nil, select-window updates the buffer list and thus indirectly runs the normal hook buffer-list-update-hook (see Buffer List). Consequently, that hook provides one way to run a function whenever a window gets selected more “permanently”.
Since buffer-list-update-hook is also run by functions that are not related to window management, it will usually make sense to save the value of the selected window somewhere and compare it with the value of selected-window while running that hook. Also, to avoid false positives when using buffer-list-update-hook, it is good practice that every select-window call supposed to select a window only temporarily passes a non-nil norecord argument. If possible, the macro with-selected-window (see below) should be used in such cases.
Emacs also runs the hook window-selection-change-functions whenever the redisplay routine detects that another window has been selected since last redisplay. See Window Hooks, for a detailed explanation. window-state-change-functions (described in the same section) is another abnormal hook run after a different window has been selected but is triggered by other window changes as well.
The sequence of calls to select-window with a non-nil norecord argument determines an ordering of windows by their selection time. The function get-lru-window can be used to retrieve the least recently selected live window (see Cyclic Window Ordering).
This macro records the selected frame, as well as the selected window of each frame, executes forms in sequence, then restores the earlier selected frame and windows. It also saves and restores the current buffer. It returns the value of the last form in forms.
This macro does not save or restore anything about the sizes, arrangement or contents of windows; therefore, if forms change them, the change persists. If the previously selected window of some frame is no longer live at the time of exit from forms, that frame’s selected window is left alone. If the previously selected window is no longer live, then whatever window is selected at the end of forms remains selected. The current buffer is restored if and only if it is still live when exiting forms.
This macro changes neither the ordering of recently selected windows nor the buffer list.
This macro selects window, executes forms in sequence, then restores the previously selected window and current buffer. The ordering of recently selected windows and the buffer list remain unchanged unless you deliberately change them within forms; for example, by calling select-window with argument norecord nil. Hence, this macro is the preferred way to temporarily work with window as the selected window without needlessly running buffer-list-update-hook.
This function returns the window on frame that is selected within that frame. frame should be a live frame; if omitted or nil, it defaults to the selected frame.
This function makes window the window selected within the frame frame. frame should be a live frame; if nil, it defaults to the selected frame. window should be a live window; if nil, it defaults to the selected window.
If frame is the selected frame, this makes window the selected window.
If the optional argument norecord is non-nil, this function does not alter the list of most recently selected windows, nor the buffer list.
This functions returns the use time of window window. window must be a live window and defaults to the selected one.
The use time of a window is not really a time value, but an integer that does increase monotonically with each call of select-window with a nil norecord argument. The window with the lowest use time is usually called the least recently used window while the window with the highest use time is called the most recently used one (see Cyclic Window Ordering).
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https://www.gnu.org/software/emacs/manual/html_node/elisp/Selecting-Windows.html