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: Translating Input, Next: Recording Input, Prev: Input Modes, Up: Terminal Input Translating Input Events ------------------------ This section describes features for translating input events into other input events before they become part of key sequences. -- Variable: extra-keyboard-modifiers This variable lets Lisp programs ``press'' the modifier keys on the keyboard. The value is a bit mask: 1 The SHIFT key. 2 The LOCK key. 4 The CTL key. 8 The META key. Each time the user types a keyboard key, it is altered as if the modifier keys specified in the bit mask were held down. When you use X windows, the program can ``press'' any of the modifier keys in this way. Otherwise, only the CTL and META keys can be virtually pressed. -- Variable: keyboard-translate-table This variable is the translate table for keyboard characters. It lets you reshuffle the keys on the keyboard without changing any command bindings. Its value must be a string or `nil'. If `keyboard-translate-table' is a string, then each character read from the keyboard is looked up in this string and the character in the string is used instead. If the string is of length N, character codes N and up are untranslated. In the example below, we set `keyboard-translate-table' to a string of 128 characters. Then we fill it in to swap the characters `C-s' and `C-\' and the characters `C-q' and `C-^'. Subsequently, typing `C-\' has all the usual effects of typing `C-s', and vice versa. (*Note Flow Control:: for more information on this subject.) (defun evade-flow-control () "Replace C-s with C-\ and C-q with C-^." (interactive) (let ((the-table (make-string 128 0))) (let ((i 0)) (while (< i 128) (aset the-table i i) (setq i (1+ i)))) ;; Swap `C-s' and `C-\'. (aset the-table ?\034 ?\^s) (aset the-table ?\^s ?\034) ;; Swap `C-q' and `C-^'. (aset the-table ?\036 ?\^q) (aset the-table ?\^q ?\036) (setq keyboard-translate-table the-table))) Note that this translation is the first thing that happens to a character after it is read from the terminal. Record-keeping features such as `recent-keys' and dribble files record the characters after translation. -- Function: keyboard-translate FROM TO This function modifies `keyboard-translate-table' to translate character code FROM into character code TO. It creates or enlarges the translate table if necessary. -- Variable: function-key-map This variable holds a keymap which describes the character sequences sent by function keys on an ordinary character terminal. This keymap uses the data structure as other keymaps, but is used differently: it specifies translations to make while reading events. If `function-key-map' ``binds'' a key sequence K to a vector V, then when K appears as a subsequence *anywhere* in a key sequence, it is replaced with the events in V. For example, VT100 terminals send `ESC O P' when the keypad PF1 key is pressed. Therefore, we want Emacs to translate that sequence of events into the single event `pf1'. We accomplish this by ``binding'' `ESC O P' to `[pf1]' in `function-key-map', when using a VT100. Thus, typing `C-c PF1' sends the character sequence `C-c ESC O P'; later the function `read-key-sequence' translates this back into `C-c PF1', which it returns as the vector `[?\C-c pf1]'. Entries in `function-key-map' are ignored if they conflict with bindings made in the minor mode, local, or global keymaps. The intent is that the character sequences that function keys send should not have command bindings in their own right. The value of `function-key-map' is usually set up automatically according to the terminal's Terminfo or Termcap entry, but sometimes those need help from terminal-specific Lisp files. Emacs comes with terminal-specific files for many common terminals; their main purpose is to make entries in `function-key-map' beyond those that can be deduced from Termcap and Terminfo. *Note Terminal-Specific::. Emacs versions 18 and earlier used totally different means of detecting the character sequences that represent function keys. -- Variable: key-translation-map This variable is another keymap used just like `function-key-map' to translate input events into other events. It differs from `function-key-map' in two ways: * `key-translation-map' goes to work after `function-key-map' is finished; it receives the results of translation by `function-key-map'. * `key-translation-map' overrides actual key bindings. The intent of `key-translation-map' is for users to map one character set to another, including ordinary characters normally bound to `self-insert-command'. You can use `function-key-map' or `key-translation-map' for more than simple aliases, by using a function, instead of a key sequence, as the ``translation'' of a key. Then this function is called to compute the translation of that key. The key translation function receives one argument, which is the prompt that was specified in `read-key-sequence'---or `nil' if the key sequence is being read by the editor command loop. In most cases you can ignore the prompt value. If the function reads input itself, it can have the effect of altering the event that follows. For example, here's how to define `C-c h' to turn the character that follows into a Hyper character: (defun hyperify (prompt) (let ((e (read-event))) (vector (if (numberp e) (logior (lsh 1 20) e) (if (memq 'hyper (event-modifiers e)) e (add-event-modifier "H-" e)))))) (defun add-event-modifier (string e) (let ((symbol (if (symbolp e) e (car e)))) (setq symbol (intern (concat string (symbol-name symbol)))) (if (symbolp e) symbol (cons symbol (cdr e))))) (define-key function-key-map "\C-ch" 'hyperify) The `iso-transl' library uses this feature to provide a way of inputting non-ASCII Latin-1 characters.  File: elisp, Node: Recording Input, Prev: Translating Input, Up: Terminal Input Recording Input --------------- -- Function: recent-keys This function returns a vector containing the last 100 input events from the keyboard or mouse. All input events are included, whether or not they were used as parts of key sequences. Thus, you always get the last 100 inputs, not counting keyboard macros. (Events from keyboard macros are excluded because they are less interesting for debugging; it should be enough to see the events which invoked the macros.) -- Command: open-dribble-file FILENAME This function opens a "dribble file" named FILENAME. When a dribble file is open, each input event from the keyboard or mouse (but not those from keyboard macros) is written in that file. A non-character event is expressed using its printed representation surrounded by `<...>'. You close the dribble file by calling this function with an argument of `nil'. This function is normally used to record the input necessary to trigger an Emacs bug, for the sake of a bug report. (open-dribble-file "~/dribble") => nil See also the `open-termscript' function (*note Terminal Output::.).  File: elisp, Node: Terminal Output, Next: Special Keysyms, Prev: Terminal Input, Up: System Interface Terminal Output =============== The terminal output functions send output to the terminal or keep track of output sent to the terminal. The variable `baud-rate' tells you what Emacs thinks is the output speed of the terminal. -- Variable: baud-rate This variable's value is the output speed of the terminal, as far as Emacs knows. Setting this variable does not change the speed of actual data transmission, but the value is used for calculations such as padding. It also affects decisions about whether to scroll part of the screen or repaint---even when using a window system, (We designed it this way despite the fact that a window system has no true ``output speed'', to give you a way to tune these decisions.) The value is measured in baud. If you are running across a network, and different parts of the network work at different baud rates, the value returned by Emacs may be different from the value used by your local terminal. Some network protocols communicate the local terminal speed to the remote machine, so that Emacs and other programs can get the proper value, but others do not. If Emacs has the wrong value, it makes decisions that are less than optimal. To fix the problem, set `baud-rate'. -- Function: baud-rate This function returns the value of the variable `baud-rate'. In Emacs versions 18 and earlier, this was the only way to find out the terminal speed. -- Function: send-string-to-terminal STRING This function sends STRING to the terminal without alteration. Control characters in STRING have terminal-dependent effects. One use of this function is to define function keys on terminals that have downloadable function key definitions. For example, this is how on certain terminals to define function key 4 to move forward four characters (by transmitting the characters `C-u C-f' to the computer): (send-string-to-terminal "\eF4\^U\^F") => nil -- Command: open-termscript FILENAME This function is used to open a "termscript file" that will record all the characters sent by Emacs to the terminal. It returns `nil'. Termscript files are useful for investigating problems where Emacs garbles the screen, problems that are due to incorrect Termcap entries or to undesirable settings of terminal options more often than to actual Emacs bugs. Once you are certain which characters were actually output, you can determine reliably whether they correspond to the Termcap specifications in use. See also `open-dribble-file' in *Note Terminal Input::. (open-termscript "../junk/termscript") => nil  File: elisp, Node: Special Keysyms, Next: Flow Control, Prev: Terminal Output, Up: System Interface System-Specific X11 Keysyms =========================== To define system-specific X11 keysyms, set the variable `system-key-alist'. -- Variable: system-key-alist This variable's value should be an alist with one element for each system-specific keysym. An element has this form: `(CODE . SYMBOL)', where CODE is the numeric keysym code (not including the ``vendor specific'' bit, 1 << 28), and SYMBOL is the name for the function key. For example `(168 . mute-acute)' defines a system-specific key used by HP X servers whose numeric code is (1 << 28) + 168. It is not a problem if the alist defines keysyms for other X servers, as long as they don't conflict with the ones used by the X server actually in use.  File: elisp, Node: Flow Control, Next: Batch Mode, Prev: Special Keysyms, Up: System Interface Flow Control ============ This section attempts to answer the question ``Why does Emacs choose to use flow-control characters in its command character set?'' For a second view on this issue, read the comments on flow control in the `emacs/INSTALL' file from the distribution; for help with Termcap entries and DEC terminal concentrators, see `emacs/etc/TERMS'. At one time, most terminals did not need flow control, and none used `C-s' and `C-q' for flow control. Therefore, the choice of `C-s' and `C-q' as command characters was uncontroversial. Emacs, for economy of keystrokes and portability, used nearly all the ASCII control characters, with mnemonic meanings when possible; thus, `C-s' for search and `C-q' for quote. Later, some terminals were introduced which required these characters for flow control. They were not very good terminals for full-screen editing, so Emacs maintainers did not pay attention. In later years, flow control with `C-s' and `C-q' became widespread among terminals, but by this time it was usually an option. And the majority of users, who can turn flow control off, were unwilling to switch to less mnemonic key bindings for the sake of flow control. So which usage is ``right'', Emacs's or that of some terminal and concentrator manufacturers? This question has no simple answer. One reason why we are reluctant to cater to the problems caused by `C-s' and `C-q' is that they are gratuitous. There are other techniques (albeit less common in practice) for flow control that preserve transparency of the character stream. Note also that their use for flow control is not an official standard. Interestingly, on the model 33 teletype with a paper tape punch (which is very old), `C-s' and `C-q' were sent by the computer to turn the punch on and off! GNU Emacs version 19 provides a convenient way of enabling flow control if you want it: call the function `enable-flow-control'. -- Function: enable-flow-control This function enables use of `C-s' and `C-q' for output flow control, and provides the characters `C-\' and `C-^' as aliases for them using `keyboard-translate-table' (*note Translating Input::.). You can use the function `enable-flow-control-on' in your `.emacs' file to enable flow control automatically on certain terminal types. -- Function: enable-flow-control-on &rest TERMTYPES This function enables flow control, and the aliases `C-\' and `C-^', if the terminal type is one of TERMTYPES. For example: (enable-flow-control-on "vt200" "vt300" "vt101" "vt131") Here is how `enable-flow-control' does its job: 1. It sets CBREAK mode for terminal input, and tells the operating system to handle flow control, with `(set-input-mode nil t)'. 2. It sets up `keyboard-translate-table' to translate `C-\' and `C-^' into `C-s' and `C-q' were typed. Except at its very lowest level, Emacs never knows that the characters typed were anything but `C-s' and `C-q', so you can in effect type them as `C-\' and `C-^' even when they are input for other commands. *Note Translating Input::. If the terminal is the source of the flow control characters, then once you enable kernel flow control handling, you probably can make do with less padding than normal for that terminal. You can reduce the amount of padding by customizing the Termcap entry. You can also reduce it by setting `baud-rate' to a smaller value so that Emacs uses a smaller speed when calculating the padding needed. *Note Terminal Output::.  File: elisp, Node: Batch Mode, Prev: Flow Control, Up: System Interface Batch Mode ========== The command line option `-batch' causes Emacs to run noninteractively. In this mode, Emacs does not read commands from the terminal, it does not alter the terminal modes, and it does not expect to be outputting to an erasable screen. The idea is that you specify Lisp programs to run; when they are finished, Emacs should exit. The way to specify the programs to run is with `-l FILE', which loads the library named FILE, and `-f FUNCTION', which calls FUNCTION with no arguments. Any Lisp program output that would normally go to the echo area, either using `message' or using `prin1', etc., with `t' as the stream, goes instead to Emacs's standard output descriptor when in batch mode. Thus, Emacs behaves much like a noninteractive application program. (The echo area output that Emacs itself normally generates, such as command echoing, is suppressed entirely.) -- Variable: noninteractive This variable is non-`nil' when Emacs is running in batch mode.  File: elisp, Node: Display, Next: Calendar, Prev: System Interface, Up: Top Emacs Display ************* This chapter describes a number of features related to the display that Emacs presents to the user. * Menu: * Refresh Screen:: Clearing the screen and redrawing everything on it. * Screen Size:: How big is the Emacs screen. * Truncation:: Folding or wrapping long text lines. * The Echo Area:: Where messages are displayed. * Selective Display:: Hiding part of the buffer text. * Overlay Arrow:: Display of an arrow to indicate position. * Temporary Displays:: Displays that go away automatically. * Overlays:: Use overlays to highlight parts of the buffer. * Faces:: A face defines a graphics appearance: font, color, etc. * Blinking:: How Emacs shows the matching open parenthesis. * Inverse Video:: Specifying how the screen looks. * Usual Display:: The usual conventions for displaying nonprinting chars. * Display Tables:: How to specify other conventions. * Beeping:: Audible signal to the user. * Window Systems:: Which window system is being used.  File: elisp, Node: Refresh Screen, Next: Screen Size, Up: Display Refreshing the Screen ===================== The function `redraw-frame' redisplays the entire contents of a given frame. *Note Frames::. -- Function: redraw-frame FRAME This function clears and redisplays frame FRAME. Even more powerful is `redraw-display': -- Command: redraw-display This function clears and redisplays all visible frames. Normally, suspending and resuming Emacs also refreshes the screen. Some terminal emulators record separate contents for display-oriented programs such as Emacs and for ordinary sequential display. If you are using such a terminal, you might want to inhibit the redisplay on resumption. *Note Suspending Emacs::. -- Variable: no-redraw-on-reenter This variable controls whether Emacs redraws the entire screen after it has been suspended and resumed. Non-`nil' means yes, `nil' means no. Processing user input takes absolute priority over redisplay. If you call these functions when input is available, they do nothing immediately, but a full redisplay does happen eventually---after all the input has been processed.  File: elisp, Node: Screen Size, Next: Truncation, Prev: Refresh Screen, Up: Display Screen Size =========== The screen size functions report or tell Emacs the height or width of the terminal. When you are using multiple frames, they apply to the selected frame (*note Frames::.). -- Function: screen-height This function returns the number of lines on the screen that are available for display. (screen-height) => 50 -- Function: screen-width This function returns the number of columns on the screen that are available for display. (screen-width) => 80 -- Function: set-screen-height LINES &optional NOT-ACTUAL-SIZE This function declares that the terminal can display LINES lines. The sizes of existing windows are altered proportionally to fit. If NOT-ACTUAL-SIZE is non-`nil', then Emacs displays LINES lines of output, but does not change its value for the actual height of the screen. (Knowing the correct actual size may be necessary for correct cursor positioning.) Using a smaller height than the terminal actually implements may be useful to reproduce behavior observed on a smaller screen, or if the terminal malfunctions when using its whole screen. If LINES is different from what it was previously, then the entire screen is cleared and redisplayed using the new size. This function returns `nil'. -- Function: set-screen-width COLUMNS &optional NOT-ACTUAL-SIZE This function declares that the terminal can display COLUMNS columns. The details are as in `set-screen-height'.  File: elisp, Node: Truncation, Next: The Echo Area, Prev: Screen Size, Up: Display Truncation ========== When a line of text extends beyond the right edge of a window, the line can either be continued on the next screen line, or truncated to one screen line. The additional screen lines used to display a long text line are called "continuation" lines. Normally, a `$' in the rightmost column of the window indicates truncation; a `\' on the rightmost column indicates a line that ``wraps'' or is continued onto the next line. (The display table can specify alternative indicators; see *Note Display Tables::.) Note that continuation is different from filling; continuation happens on the screen only, not in the buffer contents, and it breaks a line precisely at the right margin, not at a word boundary. *Note Filling::. -- User Option: truncate-lines This buffer-local variable controls how Emacs displays lines that extend beyond the right edge of the window. The default is `nil', which specifies continuation. If the value is non-`nil', then these lines are truncated. If the variable `truncate-partial-width-windows' is non-`nil', then truncation is always used for side-by-side windows (within one frame) regardless of the value of `truncate-lines'. -- Variable: default-truncate-lines This variable is the default value for `truncate-lines', for buffers that do not have local values for it. -- User Option: truncate-partial-width-windows This variable controls display of lines that extend beyond the right edge of the window, in side-by-side windows (*note Splitting Windows::.). If it is non-`nil', these lines are truncated; otherwise, `truncate-lines' says what to do with them. You can override the images that indicate continuation or truncation with the display table; see *Note Display Tables::.  File: elisp, Node: The Echo Area, Next: Selective Display, Prev: Truncation, Up: Display The Echo Area ============= The "echo area" is used for displaying messages made with the `message' primitive, and for echoing keystrokes. It is not the same as the minibuffer, despite the fact that the minibuffer appears (when active) in the same place on the screen as the echo area. The `GNU Emacs Manual' specifies the rules for resolving conflicts between the echo area and the minibuffer for use of that screen space (*note The Minibuffer: (emacs)Minibuffer.). Error messages appear in the echo area; see *Note Errors::. You can write output in the echo area by using the Lisp printing functions with `t' as the stream (*note Output Functions::.), or as follows: -- Function: message STRING &rest ARGUMENTS This function prints a one-line message in the echo area. The argument STRING is similar to a C language `printf' control string. See `format' in *Note String Conversion::, for the details on the conversion specifications. `message' returns the constructed string. If STRING is `nil', `message' clears the echo area. If the minibuffer is active, this brings the minibuffer contents back onto the screen immediately. (message "Minibuffer depth is %d." (minibuffer-depth)) -| Minibuffer depth is 0. => "Minibuffer depth is 0." ---------- Echo Area ---------- Minibuffer depth is 0. ---------- Echo Area ---------- -- Variable: cursor-in-echo-area This variable controls where the cursor appears when a message is displayed in the echo area. If it is non-`nil', then the cursor appears at the end of the message. Otherwise, the cursor appears at point---not in the echo area at all. The value is normally `nil'; Lisp programs bind it to `t' for brief periods of time.  File: elisp, Node: Selective Display, Next: Overlay Arrow, Prev: The Echo Area, Up: Display Selective Display ================= "Selective display" is a class of minor modes in which specially marked lines do not appear on the screen, or in which highly indented lines do not appear. The first variant, explicit selective display, is designed for use in a Lisp program. The program controls which lines are hidden by altering the text. Outline mode uses this variant. In the second variant, the choice of lines to hide is made automatically based on indentation. This variant is designed as a user-level feature. The way you control explicit selective display is by replacing a newline (control-j) with a carriage return (control-m). The text which was formerly a line following that newline is now invisible. Strictly speaking, it is temporarily no longer a line at all, since only newlines can separate lines; it is now part of the previous line. Selective display does not directly affect editing commands. For example, `C-f' (`forward-char') moves point unhesitatingly into invisible text. However, the replacement of newline characters with carriage return characters affects some editing commands. For example, `next-line' skips invisible lines, since it searches only for newlines. Modes that use selective display can also define commands that take account of the newlines, or that make parts of the text visible or invisible. When you write a selectively displayed buffer into a file, all the control-m's are output as newlines. This means that when you next read in the file, it looks OK, with nothing invisible. The selective display effect is seen only within Emacs. -- Variable: selective-display This buffer-local variable enables selective display. This means that lines, or portions of lines, may be made invisible. * If the value of `selective-display' is `t', then any portion of a line that follows a control-m is not displayed. * If the value of `selective-display' is a positive integer, then lines that start with more than that many columns of indentation are not displayed. When some portion of a buffer is invisible, the vertical movement commands operate as if that portion did not exist, allowing a single `next-line' command to skip any number of invisible lines. However, character movement commands (such as `forward-char') do not skip the invisible portion, and it is possible (if tricky) to insert or delete text in an invisible portion. In the examples below, we show the *display appearance* of the buffer `foo', which changes with the value of `selective-display'. The *contents* of the buffer do not change. (setq selective-display nil) => nil ---------- Buffer: foo ---------- 1 on this column 2on this column 3n this column 3n this column 2on this column 1 on this column ---------- Buffer: foo ---------- (setq selective-display 2) => 2 ---------- Buffer: foo ---------- 1 on this column 2on this column 2on this column 1 on this column ---------- Buffer: foo ---------- -- Variable: selective-display-ellipses If this buffer-local variable is non-`nil', then Emacs displays `...' at the end of a line that is followed by invisible text. This example is a continuation of the previous one. (setq selective-display-ellipses t) => t ---------- Buffer: foo ---------- 1 on this column 2on this column ... 2on this column 1 on this column ---------- Buffer: foo ---------- You can use a display table to substitute other text for the ellipsis (`...'). *Note Display Tables::.  File: elisp, Node: Overlay Arrow, Next: Temporary Displays, Prev: Selective Display, Up: Display The Overlay Arrow ================= The "overlay arrow" is useful for directing the user's attention to a particular line in a buffer. For example, in the modes used for interface to debuggers, the overlay arrow indicates the line of code about to be executed. -- Variable: overlay-arrow-string This variable holds the string to display as an arrow, or `nil' if the arrow feature is not in use. -- Variable: overlay-arrow-position This variable holds a marker which indicates where to display the arrow. It should point at the beginning of a line. The arrow text appears at the beginning of that line, overlaying any text that would otherwise appear. Since the arrow is usually short, and the line usually begins with indentation, normally nothing significant is overwritten. The overlay string is displayed only in the buffer which this marker points into. Thus, only one buffer can have an overlay arrow at any given time.  File: elisp, Node: Temporary Displays, Next: Overlays, Prev: Overlay Arrow, Up: Display Temporary Displays ================== Temporary displays are used by commands to put output into a buffer and then present it to the user for perusal rather than for editing. Many of the help commands use this feature. -- Special Form: with-output-to-temp-buffer BUFFER-NAME FORMS... This function executes FORMS while arranging to insert any output they print into the buffer named BUFFER-NAME. The buffer is then shown in some window for viewing, displayed but not selected. The string BUFFER-NAME specifies the temporary buffer, which need not already exist. The argument must be a string, not a buffer. The buffer is erased initially (with no questions asked), and it is marked as unmodified after `with-output-to-temp-buffer' exits. `with-output-to-temp-buffer' binds `standard-output' to the temporary buffer, then it evaluates the forms in FORMS. Output using the Lisp output functions within FORMS goes by default to that buffer (but screen display and messages in the echo area, although they are ``output'' in the general sense of the word, are not affected). *Note Output Functions::. The value of the last form in FORMS is returned. ---------- Buffer: foo ---------- This is the contents of foo. ---------- Buffer: foo ---------- (with-output-to-temp-buffer "foo" (print 20) (print standard-output)) => # ---------- Buffer: foo ---------- 20 # ---------- Buffer: foo ---------- -- Variable: temp-buffer-show-function If this variable, if non-`nil', `with-output-to-temp-buffer' calls it as a function to do the job of displaying a help buffer. The function gets one argument, which is the buffer it should display. In Emacs versions 18 and earlier, this variable was called `temp-buffer-show-hook'. -- Function: momentary-string-display STRING POSITION &optional CHAR MESSAGE This function momentarily displays STRING in the current buffer at POSITION. It has no effect on the undo list or on the buffer's modification status. The momentary display remains until the next input event. If the next input event is CHAR, `momentary-string-display' ignores it and returns. Otherwise, that event remains buffered for subsequent use as input. Thus, typing CHAR will simply remove the string from the display, while typing (say) `C-f' will remove the string from the display and later (presumably) move point forward. The argument CHAR is a space by default. The return value of `momentary-string-display' is not meaningful. If MESSAGE is non-`nil', it is displayed in the echo area while STRING is displayed in the buffer. If it is `nil', a default message says to type CHAR to continue. In this example, point is initially located at the beginning of the second line: ---------- Buffer: foo ---------- This is the contents of foo. -!-Second line. ---------- Buffer: foo ---------- (momentary-string-display "**** Important Message! ****" (point) ?\r "Type RET when done reading") => t ---------- Buffer: foo ---------- This is the contents of foo. **** Important Message! ****Second line. ---------- Buffer: foo ---------- ---------- Echo Area ---------- Type RET when done reading ---------- Echo Area ----------  File: elisp, Node: Overlays, Next: Faces, Prev: Temporary Displays, Up: Display Overlays ======== You can use "overlays" to alter the appearance of a buffer's text on the screen. An overlay is an object which belongs to a particular buffer, and has a specified beginning and end. It also has properties that you can examine and set; these affect the display of the text within the overlay. * Menu: * Overlay Properties:: How to read and set properties. What properties do to the screen display. * Managing Overlays:: Creating, moving, finding overlays.  File: elisp, Node: Overlay Properties, Next: Managing Overlays, Up: Overlays Overlay Properties ------------------ Overlay properties are like text properties in some respects, but the differences are more important than the similarities. Text properties are considered a part of the text; overlays are specifically considered not to be part of the text. Thus, copying text between various buffers and strings preserves text properties, but does not try to preserve overlays. Changing a buffer's text properties marks the buffer as modified, while moving an overlay or changing its properties does not. Unlike text propery changes, overlay changes are not recorded in the buffer's undo list. `priority' This property's value (which should be a nonnegative number) determines the priority of the overlay. The priority matters when two or more overlays cover the same character and both specify a face for display; the one whose `priority' value is larger takes priority over the other, and its face attributes override the face attributes of the lower priority overlay. Currently, all overlays take priority over text properties. Please avoid using negative priority values, as we have not yet decided just what they should mean. `window' If the `window' property is non-`nil', then the overlay applies only on that window. `face' This property controls the font and color of text. *Note Faces::, for more information. This feature is temporary; in the future, we may replace it with other ways of specifying how to display text. `mouse-face' This property is used instead of `face' when the mouse is within the range of the overlay. This feature may be temporary, like `face'. `modification-hooks' This property's value is a list of functions to be called if any character within the overlay is changed or if text is inserted strictly within the overlay. Each function receives three arguments: the overlay, and the beginning and end of the part of the buffer being modified. `insert-in-front-hooks' This property's value is a list of functions to be called if text is inserted right at the beginning of the overlay. `insert-behind-hooks' This property's value is a list of functions to be called if text is inserted right at the end of the overlay. `invisible' A non-`nil' `invisible' property means that the text in the overlay does not appear on the screen. This works much like selective display. Details of this feature are likely to change in future versions, so check the `etc/NEWS' file in the version you are using. `before-string' This property's value is a string to add to the display at the beginning of the overlay. The string does not appear in the buffer in any sense---only on the screen. This is not yet implemented, but will be. `after-string' This property's value is a string to add to the display at the end of the overlay. The string does not appear in the buffer in any sense---only on the screen. This is not yet implemented, but will be. These are the functions for reading and writing the properties of an overlay. -- Function: overlay-get OVERLAY PROP This function returns the value of property PROP recorded in OVERLAY. If OVERLAY does not record any value for that property, then the value is `nil'. -- Function: overlay-put OVERLAY PROP VALUE This function sets the value of property PROP recorded in OVERLAY to VALUE. It returns VALUE. See also the function `get-char-property' which checks both overlay properties and text properties for a given character. *Note Examining Properties::.