This is Info file elisp, produced by Makeinfo-1.55 from the input file elisp.texi. This version is the edition 2.3 of the GNU Emacs Lisp Reference Manual. It corresponds to Emacs Version 19.23. Published by the Free Software Foundation 675 Massachusetts Avenue Cambridge, MA 02139 USA Copyright (C) 1990, 1991, 1992, 1993, 1994 Free Software Foundation, Inc. Permission is granted to make and distribute verbatim copies of this manual provided the copyright notice and this permission notice are preserved on all copies. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that this permission notice may be stated in a translation approved by the Foundation. Permission is granted to copy and distribute modified versions of this manual under the conditions for verbatim copying, provided also that the section entitled "GNU General Public License" is included exactly as in the original, and provided that the entire resulting derived work is distributed under the terms of a permission notice identical to this one. Permission is granted to copy and distribute translations of this manual into another language, under the above conditions for modified versions, except that the section entitled "GNU General Public License" may be included in a translation approved by the Free Software Foundation instead of in the original English.  File: elisp, Node: Current Buffer, Prev: Killing Buffers, Up: Buffers The Current Buffer ================== There are, in general, many buffers in an Emacs session. At any time, one of them is designated as the "current buffer". This is the buffer in which most editing takes place, because most of the primitives for examining or changing text in a buffer operate implicitly on the current buffer (*note Text::.). Normally the buffer that is displayed on the screen in the selected window is the current buffer, but this is not always so: a Lisp program can designate any buffer as current temporarily in order to operate on its contents, without changing what is displayed on the screen. The way to designate a current buffer in a Lisp program is by calling `set-buffer'. The specified buffer remains current until a new one is designated. When an editing command returns to the editor command loop, the command loop designates the buffer displayed in the selected window as current, to prevent confusion: the buffer that the cursor is in, when Emacs reads a command, is the one to which the command will apply. (*Note Command Loop::.) Therefore, `set-buffer' is not the way to switch visibly to a different buffer so that the user can edit it. For this, you must use the functions described in *Note Displaying Buffers::. However, Lisp functions that change to a different current buffer should not depend on the command loop to set it back afterwards. Editing commands written in Emacs Lisp can be called from other programs as well as from the command loop. It is convenient for the caller if the subroutine does not change which buffer is current (unless, of course, that is the subroutine's purpose). Therefore, you should normally use `set-buffer' within a `save-excursion' that will restore the current buffer when your function is done (*note Excursions::.). Here is an example, the code for the command `append-to-buffer' (with the documentation string abridged): (defun append-to-buffer (buffer start end) "Append to specified buffer the text of the region. ..." (interactive "BAppend to buffer: \nr") (let ((oldbuf (current-buffer))) (save-excursion (set-buffer (get-buffer-create buffer)) (insert-buffer-substring oldbuf start end)))) This function binds a local variable to the current buffer, and then `save-excursion' records the values of point, the mark, and the original buffer. Next, `set-buffer' makes another buffer current. Finally, `insert-buffer-substring' copies the string from the original current buffer to the new current buffer. If the buffer appended to happens to be displayed in some window, the next redisplay will show how its text has changed. Otherwise, you will not see the change immediately on the screen. The buffer becomes current temporarily during the execution of the command, but this does not cause it to be displayed. If you make local bindings (with `let' or function arguments) for a variable that may also have buffer-local bindings, make sure that the same buffer is current at the beginning and at the end of the local binding's scope. Otherwise you might bind it in one buffer and unbind it in another! There are two ways to do this. In simple cases, you may see that nothing ever changes the current buffer within the scope of the binding. Otherwise, use `save-excursion' to make sure that the buffer current at the beginning is current again whenever the variable is unbound. It is not reliable to change the current buffer back with `set-buffer', because that won't do the job if a quit happens while the wrong buffer is current. Here is what not to do: (let (buffer-read-only (obuf (current-buffer))) (set-buffer ...) ... (set-buffer obuf)) Using `save-excursion', as shown below, handles quitting, errors and `throw' as well as ordinary evaluation. (let (buffer-read-only) (save-excursion (set-buffer ...) ...)) - Function: current-buffer This function returns the current buffer. (current-buffer) => # - Function: set-buffer BUFFER-OR-NAME This function makes BUFFER-OR-NAME the current buffer. It does not display the buffer in the currently selected window or in any other window, so the user cannot necessarily see the buffer. But Lisp programs can in any case work on it. This function returns the buffer identified by BUFFER-OR-NAME. An error is signaled if BUFFER-OR-NAME does not identify an existing buffer.  File: elisp, Node: Windows, Next: Frames, Prev: Buffers, Up: Top Windows ******* This chapter describes most of the functions and variables related to Emacs windows. See *Note Display::, for information on how text is displayed in windows. * Menu: * Basic Windows:: Basic information on using windows. * Splitting Windows:: Splitting one window into two windows. * Deleting Windows:: Deleting a window gives its space to other windows. * Selecting Windows:: The selected window is the one that you edit in. * Cyclic Window Ordering:: Moving around the existing windows. * Buffers and Windows:: Each window displays the contents of a buffer. * Displaying Buffers:: Higher-lever functions for displaying a buffer and choosing a window for it. * Choosing Window:: How to choose a window for displaying a buffer. * Window Point:: Each window has its own location of point. * Window Start:: The display-start position controls which text is on-screen in the window. * Vertical Scrolling:: Moving text up and down in the window. * Horizontal Scrolling:: Moving text sideways on the window. * Size of Window:: Accessing the size of a window. * Resizing Windows:: Changing the size of a window. * Coordinates and Windows::Converting coordinates to windows. * Window Configurations:: Saving and restoring the state of the screen.  File: elisp, Node: Basic Windows, Next: Splitting Windows, Up: Windows Basic Concepts of Emacs Windows =============================== A "window" is the physical area of the screen in which a buffer is displayed. The term is also used to refer to a Lisp object which represents that screen area in Emacs Lisp. It should be clear from the context which is meant. There is always at least one window in any frame. In each frame, at any time, one and only one window is designated as "selected within the frame". The frame's cursor appears in that window. There is also one selected frame; and the window selected within that frame is "the selected window". The selected window's buffer is usually the current buffer (except when `set-buffer' has been used). *Note Current Buffer::. For all intents, a window only exists while it is displayed on the terminal. Once removed from the display, the window is effectively deleted and should not be used, *even though there may still be references to it* from other Lisp objects. Restoring a saved window configuration is the only way for a window no longer on the screen to come back to life. (*Note Deleting Windows::.) Each window has the following attributes: * containing frame * window height * window width * window edges with respect to the screen or frame * the buffer it displays * position within the buffer at the upper left of the window * the amount of horizontal scrolling, in columns * point * the mark * how recently the window was selected Users create multiple windows so they can look at several buffers at once. Lisp libraries use multiple windows for a variety of reasons, but most often to give different views of the same information. In Rmail, for example, you can move through a summary buffer in one window while the other window shows messages one at a time as they are reached. The meaning of "window" in Emacs is similar to what it means in the context of general purpose window systems such as X, but not identical. The X Window System subdivides the screen into X windows; Emacs uses one or more X windows, called "frames" in Emacs terminology, and subdivides each of them into (nonoverlapping) Emacs windows. When you use Emacs on an ordinary display terminal, Emacs subdivides the terminal screen into Emacs windows. Most window systems support arbitrarily located overlapping windows. In contrast, Emacs windows are "tiled"; they never overlap, and together they fill the whole of the screen or frame. Because of the way in which Emacs creates new windows and resizes them, you can't create every conceivable tiling of windows on an Emacs frame. *Note Splitting Windows::, and *Note Size of Window::. *Note Display::, for information on how the contents of the window's buffer are displayed in the window. - Function: windowp OBJECT This function returns `t' if OBJECT is a window.  File: elisp, Node: Splitting Windows, Next: Deleting Windows, Prev: Basic Windows, Up: Windows Splitting Windows ================= The functions described here are the primitives used to split a window into two windows. Two higher level functions sometimes split a window, but not always: `pop-to-buffer' and `display-buffer' (*note Displaying Buffers::.). The functions described here do not accept a buffer as an argument. The two "halves" of the split window initially display the same buffer previously visible in the window that was split. - Command: split-window &optional WINDOW SIZE HORIZONTAL This function splits WINDOW into two windows. The original window WINDOW remains the selected window, but occupies only part of its former screen area. The rest is occupied by a newly created window which is returned as the value of this function. If HORIZONTAL is non-`nil', then WINDOW splits into two side by side windows. The original window WINDOW keeps the leftmost SIZE columns, and gives the rest of the columns to the new window. Otherwise, it splits into windows one above the other, and WINDOW keeps the upper SIZE lines and gives the rest of the lines to the new window. The original window is therefore the right-hand or upper of the two, and the new window is the left-hand or lower. If WINDOW is omitted or `nil', then the selected window is split. If SIZE is omitted or `nil', then WINDOW is divided evenly into two parts. (If there is an odd line, it is allocated to the new window.) When `split-window' is called interactively, all its arguments are `nil'. The following example starts with one window on a screen that is 50 lines high by 80 columns wide; then the window is split. (setq w (selected-window)) => # (window-edges) ; Edges in order: => (0 0 80 50) ; left--top--right--bottom ;; Returns window created (setq w2 (split-window w 15)) => # (window-edges w2) => (0 15 80 50) ; Bottom window; ; top is line 15 (window-edges w) => (0 0 80 15) ; Top window The screen looks like this: __________ | | line 0 | w | |__________| | | line 15 | w2 | |__________| line 50 column 0 column 80 Next, the top window is split horizontally: (setq w3 (split-window w 35 t)) => # (window-edges w3) => (35 0 80 15) ; Left edge at column 35 (window-edges w) => (0 0 35 15) ; Right edge at column 35 (window-edges w2) => (0 15 80 50) ; Bottom window unchanged Now, the screen looks like this: column 35 __________ | | | line 0 | w | w3 | |___|______| | | line 15 | w2 | |__________| line 50 column 0 column 80 - Command: split-window-vertically SIZE This function splits the selected window into two windows, one above the other, leaving the selected window with SIZE lines. This function is simply an interface to `split-windows'. Here is the complete function definition for it: (defun split-window-vertically (&optional arg) "Split current window into two windows, one above the other." (interactive "P") (split-window nil (and arg (prefix-numeric-value arg)))) - Command: split-window-horizontally SIZE This function splits the selected window into two windows side-by-side, leaving the selected window with SIZE columns. This function is simply an interface to `split-windows'. Here is the complete definition for `split-window-horizontally' (except for part of the documentation string): (defun split-window-horizontally (&optional arg) "Split selected window into two windows, side by side..." (interactive "P") (split-window nil (and arg (prefix-numeric-value arg)) t)) - Function: one-window-p &optional NO-MINI ALL-FRAMES This function returns non-`nil' if there is only one window. The argument NO-MINI, if non-`nil', means don't count the minibuffer even if it is active; otherwise, the minibuffer window is included, if active, in the total number of windows which is compared against one. The argument ALL-FRAMES specifies which frames to consider. Here are the possible values and their meanings: `nil' Count the windows in the selected frame, plus the minibuffer used by that frame even if it lies in some other frame. `t' Count all windows in all existing frames. `visible' Count all windows in all visible frames. anything else Count precisely the windows in the selected frame, and no others.  File: elisp, Node: Deleting Windows, Next: Selecting Windows, Prev: Splitting Windows, Up: Windows Deleting Windows ================ A window remains visible on its frame unless you "delete" it by calling certain functions that delete windows. A deleted window cannot appear on the screen, but continues to exist as a Lisp object until there are no references to it. There is no way to cancel the deletion of a window aside from restoring a saved window configuration (*note Window Configurations::.). Restoring a window configuration also deletes any windows that aren't part of that configuration. When you delete a window, the space it took up is given to one adjacent sibling. (In Emacs version 18, the space was divided evenly among all the siblings.) - Function: window-live-p WINDOW This function returns `nil' if WINDOW is deleted, and `t' otherwise. *Warning:* erroneous information or fatal errors may result from using a deleted window as if it were live. - Command: delete-window &optional WINDOW This function removes WINDOW from the display. If WINDOW is omitted, then the selected window is deleted. An error is signaled if there is only one window when `delete-window' is called. This function returns `nil'. When `delete-window' is called interactively, WINDOW defaults to the selected window. - Command: delete-other-windows &optional WINDOW This function makes WINDOW the only window on its frame, by deleting the other windows in that frame. If WINDOW is omitted or `nil', then the selected window is used by default. The result is `nil'. - Command: delete-windows-on BUFFER &optional FRAME This function deletes all windows showing BUFFER. If there are no windows showing BUFFER, it does nothing. `delete-windows-on' operates frame by frame. If a frame has several windows showing different buffers, then those showing BUFFER are removed, and the others expand to fill the space. If all windows in some frame are showing BUFFER (including the case where there is only one window), then the frame reverts to having a single window showing another buffer chosen with `other-buffer'. *Note The Buffer List::. The argument FRAME controls which frames to operate on: * If it is `nil', operate on the selected frame. * If it is `t', operate on all frames. * If it is `visible', operate on all visible frames. * If it is a frame, operate on that frame. This function always returns `nil'.  File: elisp, Node: Selecting Windows, Next: Cyclic Window Ordering, Prev: Deleting Windows, Up: Windows Selecting Windows ================= When a window is selected, the buffer in the window becomes the current buffer, and the cursor will appear in it. - Function: selected-window This function returns the selected window. This is the window in which the cursor appears and to which many commands apply. - Function: select-window WINDOW This function makes WINDOW the selected window. The cursor then appears in WINDOW (on redisplay). The buffer being displayed in WINDOW is immediately designated the current buffer. The return value is WINDOW. (setq w (next-window)) (select-window w) => # The following functions choose one of the windows on the screen, offering various criteria for the choice. - Function: get-lru-window &optional FRAME This function returns the window least recently "used" (that is, selected). The selected window is always the most recently used window. The selected window can be the least recently used window if it is the only window. A newly created window becomes the least recently used window until it is selected. A minibuffer window is never a candidate. The argument FRAME controls which set of windows are considered. * If it is `nil', consider windows on the selected frame. * If it is `t', consider windows on all frames. * If it is `visible', consider windows on all visible frames. * If it is a frame, consider windows on that frame. - Function: get-largest-window &optional FRAME This function returns the window with the largest area (height times width). If there are no side-by-side windows, then this is the window with the most lines. A minibuffer window is never a candidate. If there are two windows of the same size, then the function returns the window which is first in the cyclic ordering of windows (see following section), starting from the selected window. The argument FRAME controls which set of windows are considered. See `get-lru-window', above.  File: elisp, Node: Cyclic Window Ordering, Next: Buffers and Windows, Prev: Selecting Windows, Up: Windows Cyclic Ordering of Windows ========================== When you use the command `C-x o' (`other-window') to select the next window, it moves through all the windows on the screen in a specific cyclic order. For any given configuration of windows, this order never varies. It is called the "cyclic ordering of windows". This ordering generally goes from top to bottom, and from left to right. But it may go down first or go right first, depending on the order in which the windows were split. If the first split was vertical (into windows one above each other), and then the subwindows were split horizontally, then the ordering is left to right in the top of the frame, and then left to right in the next lower part of the frame, and so on. If the first split was horizontal, the ordering is top to bottom in the left part, and so on. In general, within each set of siblings at any level in the window tree, the order is left to right, or top to bottom. - Function: next-window &optional WINDOW MINIBUF ALL-FRAMES This function returns the window following WINDOW in the cyclic ordering of windows. This is the window which `C-x o' would select if done when WINDOW is selected. If WINDOW is the only window visible, then this function returns WINDOW. If omitted, WINDOW defaults to the selected window. The value of the argument MINIBUF determines whether the minibuffer is included in the window order. Normally, when MINIBUF is `nil', the minibuffer is included if it is currently active; this is the behavior of `C-x o'. (The minibuffer window is active while the minibuffer is in use. *Note Minibuffers::.) If MINIBUF is `t', then the cyclic ordering includes the minibuffer window even if it is not active. If MINIBUF is neither `t' nor `nil', then the minibuffer window is not included even if it is active. The argument ALL-FRAMES specifies which frames to consider. Here are the possible values and their meanings: `nil' Consider all the windows in WINDOW's frame, plus the minibuffer used by that frame even if it lies in some other frame. `t' Consider all windows in all existing frames. `visible' Consider all windows in all visible frames. (To get useful results, you must ensure WINDOW is in a visible frame.) anything else Consider precisely the windows in WINDOW's frame, and no others. This example assumes there are two windows, both displaying the buffer `windows.texi': (selected-window) => # (next-window (selected-window)) => # (next-window (next-window (selected-window))) => # - Function: previous-window &optional WINDOW MINIBUF ALL-FRAMES This function returns the window preceding WINDOW in the cyclic ordering of windows. The other arguments specify which windows to include in the cycle, as in `next-window'. - Command: other-window COUNT This function selects the COUNTth following window in the cyclic order. If count is negative, then it selects the -COUNTth preceding window. It returns `nil'. In an interactive call, COUNT is the numeric prefix argument. - Function: walk-windows PROC &optional MINIBUF ALL-FRAMES This function cycles through all windows, calling `proc' once for each window with the window as its sole argument. The optional arguments MINIBUF and ALL-FRAMES specify the set of windows to include in the scan. See `next-window', above, for details.  File: elisp, Node: Buffers and Windows, Next: Displaying Buffers, Prev: Cyclic Window Ordering, Up: Windows Buffers and Windows =================== This section describes low-level functions to examine windows or to display buffers in windows in a precisely controlled fashion. *Note Displaying Buffers::, for related functions that find a window to use and specify a buffer for it. The functions described there are easier to use than these, but they employ heuristics in choosing or creating a window; use these functions when you need complete control. - Function: set-window-buffer WINDOW BUFFER-OR-NAME This function makes WINDOW display BUFFER-OR-NAME as its contents. It returns `nil'. (set-window-buffer (selected-window) "foo") => nil - Function: window-buffer &optional WINDOW This function returns the buffer that WINDOW is displaying. If WINDOW is omitted, this function returns the buffer for the selected window. (window-buffer) => # - Function: get-buffer-window BUFFER-OR-NAME &optional ALL-FRAMES This function returns a window currently displaying BUFFER-OR-NAME, or `nil' if there is none. If there are several such windows, then the function returns the first one in the cyclic ordering of windows, starting from the selected window. *Note Cyclic Window Ordering::. The argument ALL-FRAMES controls which windows to consider. * If it is `nil', consider windows on the selected frame. * If it is `t', consider windows on all frames. * If it is `visible', consider windows on all visible frames. * If it is a frame, consider windows on that frame. - Command: replace-buffer-in-windows BUFFER This function replaces BUFFER with some other buffer in all windows displaying it. The other buffer used is chosen with `other-buffer'. In the usual applications of this function, you don't care which other buffer is used; you just want to make sure that BUFFER is no longer displayed. This function returns `nil'.  File: elisp, Node: Displaying Buffers, Next: Choosing Window, Prev: Buffers and Windows, Up: Windows Displaying Buffers in Windows ============================= In this section we describe convenient functions that choose a window automatically and use it to display a specified buffer. These functions can also split an existing window in certain circumstances. We also describe variables that parameterize the heuristics used for choosing a window. *Note Buffers and Windows::, for low-level functions that give you more precise control. Do not use the functions in this section in order to make a buffer current so that a Lisp program can access or modify it; they are too drastic for that purpose, since they change the display of buffers in windows, which is gratuitous and will surprise the user. Instead, use `set-buffer' (*note Current Buffer::.) and `save-excursion' (*note Excursions::.), which designate buffers as current for programmed access without affecting the display of buffers in windows. - Command: switch-to-buffer BUFFER-OR-NAME &optional NORECORD This function makes BUFFER-OR-NAME the current buffer, and also displays the buffer in the selected window. This means that a human can see the buffer and subsequent keyboard commands will apply to it. Contrast this with `set-buffer', which makes BUFFER-OR-NAME the current buffer but does not display it in the selected window. *Note Current Buffer::. If BUFFER-OR-NAME does not identify an existing buffer, then a new buffer by that name is created. Normally the specified buffer is put at the front of the buffer list. This affects the operation of `other-buffer'. However, if NORECORD is non-`nil', this is not done. *Note The Buffer List::. The `switch-to-buffer' function is often used interactively, as the binding of `C-x b'. It is also used frequently in programs. It always returns `nil'. - Command: switch-to-buffer-other-window BUFFER-OR-NAME This function makes BUFFER-OR-NAME the current buffer and displays it in a window not currently selected. It then selects that window. The handling of the buffer is the same as in `switch-to-buffer'. The previously selected window is absolutely never used to display the buffer. If it is the only window, then it is split to make a distinct window for this purpose. If the selected window is already displaying the buffer, then it continues to do so, but another window is nonetheless found to display it in as well. - Function: pop-to-buffer BUFFER-OR-NAME &optional OTHER-WINDOW This function makes BUFFER-OR-NAME the current buffer and switches to it in some window, preferably not the window previously selected. The "popped-to" window becomes the selected window within its frame. If the variable `pop-up-frames' is non-`nil', `pop-to-buffer' looks for a window in any visible frame already displaying the buffer; if there is one, it returns that window and makes it be selected within its frame. If there is none, it creates a new frame and displays the buffer in it. If `pop-up-frames' is `nil', then `pop-to-buffer' operates entirely within the selected frame. (If the selected frame has just a minibuffer, `pop-to-buffer' operates within the most recently selected frame that was not just a minibuffer.) If the variable `pop-up-windows' is non-`nil', windows may be split to create a new window that is different from the original window. For details, see *Note Choosing Window::. If OTHER-WINDOW is non-`nil', `pop-to-buffer' finds or creates another window even if BUFFER-OR-NAME is already visible in the selected window. Thus BUFFER-OR-NAME could end up displayed in two windows. On the other hand, if BUFFER-OR-NAME is already displayed in the selected window and OTHER-WINDOW is `nil', then the selected window is considered sufficient display for BUFFER-OR-NAME, so that nothing needs to be done. If BUFFER-OR-NAME is a string that does not name an existing buffer, a buffer by that name is created. An example use of this function is found at the end of *Note Filter Functions::.  File: elisp, Node: Choosing Window, Next: Window Point, Prev: Displaying Buffers, Up: Windows Choosing a Window for Display ============================= This section describes the basic facility which chooses a window to display a buffer in--`display-buffer'. All the higher-level functions and commands use this subroutine. Here we describe how to use `display-buffer' and how to customize it. - Command: display-buffer BUFFER-OR-NAME &optional NOT-THIS-WINDOW This command makes BUFFER-OR-NAME appear in some window, like `pop-to-buffer', but it does not select that window and does not make the buffer current. The identity of the selected window is unaltered by this function. If NOT-THIS-WINDOW is non-`nil', it means to display the specified buffer in a window other than the selected one, even if it is already on display in the selected window. This can cause the buffer to appear in two windows at once. Otherwise, if BUFFER-OR-NAME is already being displayed in any window, that is good enough, so this function does nothing. `display-buffer' returns the window chosen to display BUFFER-OR-NAME. Precisely how `display-buffer' finds or creates a window depends on the variables described below. - User Option: pop-up-windows This variable controls whether `display-buffer' makes new windows. If it is non-`nil' and there is only one window, then that window is split. If it is `nil', then `display-buffer' does not split the single window, but uses it whole. - User Option: split-height-threshold This variable determines when `display-buffer' may split a window, if there are multiple windows. `display-buffer' always splits the largest window if it has at least this many lines. If the largest window is not this tall, it is split only if it is the sole window and `pop-up-windows' is non-`nil'. - User Option: pop-up-frames This variable controls whether `display-buffer' makes new frames. If it is non-`nil', `display-buffer' looks for an existing window already displaying the desired buffer, on any visible frame. If it finds one, it returns that window. Otherwise it makes a new frame. The variables `pop-up-windows' and `split-height-threshold' do not matter if `pop-up-frames' is non-`nil'. If `pop-up-frames' is `nil', then `display-buffer' either splits a window or reuses one. *Note Frames::, for more information. - Variable: pop-up-frame-function This variable specifies how to make a new frame if `pop-up-frames' is non-`nil'. Its value should be a function of no arguments. When `display-buffer' makes a new frame, it does so by calling that function, which should return a frame. The default value of the variable is a function which creates a frame using parameters from `pop-up-frame-alist'. - Variable: pop-up-frame-alist This variable holds an alist specifying frame parameters used when `display-buffer' makes a new frame. *Note Frame Parameters::, for more information about frame parameters. - Variable: special-display-buffer-names A list of buffer names for buffers that should be displayed specially. If the buffer's name is in this list, `display-buffer' handles the buffer specially. By default, special display means to give the buffer a dedicated frame. - Variable: special-display-regexps A list of regular expressions that specify buffers that should be displayed specially. If the buffer's name matches any of the regular expressions in this list, `display-buffer' handles the buffer specially. By default, special display means to give the buffer a dedicated frame. - Variable: special-display-function This variable holds the function to call to display a buffer specially. It receives the buffer as an argument, and should return the window in which it is displayed. The default value of this variable is `special-display-popup-frame'. - Function: special-display-popup-frame BUFFER This function makes BUFFER visible in a frame of its own. If BUFFER is already displayed in a window in some frame, it makes the frame visible and raises it, to use that window. Otherwise, it creates a frame that will be dedicated to BUFFER. - User Option: special-display-frame-alist This variable holds frame parameters for `special-display-popup-frame' to use when it creates a frame. - Variable: display-buffer-function This variable is the most flexible way to customize the behavior of `display-buffer'. If it is non-`nil', it should be a function that `display-buffer' calls to do the work. The function should accept two arguments, the same two arguments that `display-buffer' received. It should choose or create a window, display the specified buffer, and then return the window. This hook takes precedence over all the other options and hooks described above. A window can be marked as "dedicated" to its buffer. Then `display-buffer' does not try to use that window. - Function: window-dedicated-p WINDOW This function returns `t' if WINDOW is marked as dedicated; otherwise `nil'. - Function: set-window-dedicated-p WINDOW FLAG This function marks WINDOW as dedicated if FLAG is non-`nil', and nondedicated otherwise.  File: elisp, Node: Window Point, Next: Window Start, Prev: Choosing Window, Up: Windows Windows and Point ================= Each window has its own value of 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 to 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. * *Note Positions::, for more details on buffer positions. 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 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. When WINDOW is the selected window and its buffer is also the current buffer, the value returned is the same as point in that 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.  File: elisp, Node: Window Start, Next: Vertical Scrolling, Prev: Window Point, Up: Windows The Window Start Position ========================= Each window contains a marker used to keep track of a buffer position which specifies where in the buffer display should start. This position is called the "display-start" position of the window (or just the "start"). The character after this position is the one that appears at the upper left corner of the window. It is usually, but not inevitably, at the beginning of a text line. - Function: window-start &optional WINDOW This function returns the display-start position of window WINDOW. If WINDOW is `nil', the selected window is used. For example, (window-start) => 7058 When you create a window, or display a different buffer in it, the the display-start position is set to a display-start position recently used for the same buffer, or 1 if the buffer doesn't have any. For a realistic example, see the description of `count-lines' in *Note Text Lines::. - Function: window-end &optional WINDOW This function returns the position of the end of the display in window WINDOW. If WINDOW is `nil', the selected window is used. - Function: set-window-start WINDOW POSITION &optional NOFORCE This function sets the display-start position of WINDOW to POSITION in WINDOW's buffer. The display routines insist that the position of point be visible when a buffer is displayed. Normally, they change the display-start position (that is, scroll the window) whenever necessary to make point visible. However, if you specify the start position with this function using `nil' for NOFORCE, it means you want display to start at POSITION even if that would put the location of point off the screen. If this does place point off screen, the display routines move point to the left margin on the middle line in the window. For example, if point is 1 and you set the start of the window to 2, then point would be "above" the top of the window. The display routines will automatically move point if it is still 1 when redisplay occurs. Here is an example: ;; Here is what `foo' looks like before executing ;; the `set-window-start' expression. ---------- Buffer: foo ---------- -!-This is the contents of buffer foo. 2 3 4 5 6 ---------- Buffer: foo ---------- (set-window-start (selected-window) (1+ (window-start))) => 2 ;; Here is what `foo' looks like after executing ;; the `set-window-start' expression. ---------- Buffer: foo ---------- his is the contents of buffer foo. 2 3 -!-4 5 6 ---------- Buffer: foo ---------- If NOFORCE is non-`nil', and POSITION would place point off screen at the next redisplay, then redisplay computes a new window-start position that works well with point, and thus POSITION is not used. This function returns POSITION. - Function: pos-visible-in-window-p &optional POSITION WINDOW This function returns `t' if POSITION is within the range of text currently visible on the screen in WINDOW. It returns `nil' if POSITION is scrolled vertically out of view. The argument POSITION defaults to the current position of point; WINDOW, to the selected window. Here is an example: (or (pos-visible-in-window-p (point) (selected-window)) (recenter 0)) The `pos-visible-in-window-p' function considers only vertical scrolling. If POSITION is out of view only because WINDOW has been scrolled horizontally, `pos-visible-in-window-p' returns `t'. *Note Horizontal Scrolling::.  File: elisp, Node: Vertical Scrolling, Next: Horizontal Scrolling, Prev: Window Start, Up: Windows Vertical Scrolling ================== Vertical scrolling means moving the text up or down in a window. It works by changing the value of the window's display-start location. It may also change the value of `window-point' to keep it on the screen. In the commands `scroll-up' and `scroll-down', the directions "up" and "down" refer to the motion of the text in the buffer at which you are looking through the window. Imagine that the text is written on a long roll of paper and that the scrolling commands move the paper up and down. Thus, if you are looking at text in the middle of a buffer and repeatedly call `scroll-down', you will eventually see the beginning of the buffer. Some people have urged that the opposite convention be used: they imagine that the window moves over text that remains in place. Then "down" commands would take you to the end of the buffer. This view is more consistent with the actual relationship between windows and the text in the buffer, but it is less like what the user sees. The position of a window on the terminal does not move, and short scrolling commands clearly move the text up or down on the screen. We have chosen names that fit the user's point of view. The scrolling functions (aside from `scroll-other-window') have unpredictable results if the current buffer is different from the buffer that is displayed in the selected window. *Note Current Buffer::. - Command: scroll-up &optional COUNT This function scrolls the text in the selected window upward COUNT lines. If COUNT is negative, scrolling is actually downward. If COUNT is `nil' (or omitted), then the length of scroll is `next-screen-context-lines' lines less than the usable height of the window (not counting its mode line). `scroll-up' returns `nil'. - Command: scroll-down &optional COUNT This function scrolls the text in the selected window downward COUNT lines. If COUNT is negative, scrolling is actually upward. If COUNT is omitted or `nil', then the length of the scroll is `next-screen-context-lines' lines less than the usable height of the window. `scroll-down' returns `nil'. - Command: scroll-other-window &optional COUNT This function scrolls the text in another window upward COUNT lines. Negative values of COUNT, or `nil', are handled as in `scroll-up'. The window that is scrolled is normally the one following the selected window in the cyclic ordering of windows--the window that `next-window' would return. *Note Cyclic Window Ordering::. You can specify a buffer to scroll with the variable `other-window-scroll-buffer'. When the selected window is the minibuffer, the next window is normally the one at the top left corner. You can specify a different window to scroll with the variable `minibuffer-scroll-window'. This variable has no effect when any other window is selected. *Note Minibuffer Misc::. When the minibuffer is active, it is the next window if the selected window is the one at the bottom right corner. In this case, `scroll-other-window' attempts to scroll the minibuffer. If the minibuffer contains just one line, it has nowhere to scroll to, so the line reappears after the echo area momentarily displays the message "Beginning of buffer". - Variable: other-window-scroll-buffer If this variable is non-`nil', it tells `scroll-other-window' which buffer to scroll. - User Option: scroll-step This variable controls how scrolling is done automatically when point moves off the screen. If the value is zero, then redisplay scrolls the text to center point vertically in the window. If the value is a positive integer N, then redisplay brings point back on screen by scrolling N lines in either direction, if possible; otherwise, it centers point if possible. The default value is zero. - User Option: next-screen-context-lines The value of this variable is the number of lines of continuity to retain when scrolling by full screens. For example, `scroll-up' with an argument of `nil' scrolls so that this many lines at the bottom of the window appear instead at the top. The default value is `2'. - Command: recenter &optional COUNT This function scrolls the selected window to put the text where point is located at a specified vertical position within the window. If COUNT is a nonnegative number, it puts the line containing point COUNT lines down from the top of the window. If COUNT is a negative number, then it counts upward from the bottom of the window, so that -1 stands for the last usable line in the window. If COUNT is a non-`nil' list, then it stands for the line in the middle of the window. If COUNT is `nil', `recenter' puts the line containing point in the middle of the window, then clears and redisplays the entire selected frame. When `recenter' is called interactively, COUNT is the raw prefix argument. Thus, typing `C-u' as the prefix sets the COUNT to a non-`nil' list, while typing `C-u 4' sets COUNT to 4, which positions the current line four lines from the top. Typing `C-u 0 C-l' positions the current line at the top of the window. This action is so handy that some people bind the command to a function key. For example, (defun line-to-top-of-window () "Scroll current line to top of window. Replaces three keystroke sequence C-u 0 C-l." (interactive) (recenter 0)) (global-set-key "\C-cl" 'line-to-top-of-window)