This is Info file elisp, produced by Makeinfo version 1.68 from the input file elisp.texi. INFO-DIR-SECTION Editors START-INFO-DIR-ENTRY * Elisp: (elisp). The Emacs Lisp Reference Manual. END-INFO-DIR-ENTRY This version is the edition 2.5 of the GNU Emacs Lisp Reference Manual. It corresponds to Emacs Version 20.3 Published by the Free Software Foundation 59 Temple Place, Suite 330 Boston, MA 02111-1307 USA Copyright (C) 1990, 1991, 1992, 1993, 1994, 1995, 1996, 1998 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: Refresh Screen, Next: Truncation, 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. 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. 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. - Variable: no-redraw-on-reenter This variable controls whether Emacs redraws the entire screen after it has been suspended and resumed. Non-`nil' means there is no need to redraw, `nil' means redrawing is needed. The default is `nil'.  File: elisp, Node: Truncation, Next: The Echo Area, Prev: Refresh Screen, 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" onto the next line, which is also called "continuing" the 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'. - User Option: default-truncate-lines This variable is the default value for `truncate-lines', for buffers that do not have buffer-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. When horizontal scrolling (*note Horizontal Scrolling::.) is in use in a window, that forces truncation. You can override the glyphs that indicate continuation or truncation using the display table; see *Note Display Tables::. If your buffer contains *very* long lines, and you use continuation to display them, just thinking about them can make Emacs redisplay slow. The column computation and indentation functions also become slow. Then you might find it advisable to set `cache-long-line-scans' to `t'. - Variable: cache-long-line-scans If this variable is non-`nil', various indentation and motion functions, and Emacs redisplay, cache the results of scanning the buffer, and consult the cache to avoid rescanning regions of the buffer unless they are modified. Turning on the cache slows down processing of short lines somewhat. This variable is automatically buffer-local in every buffer.  File: elisp, Node: The Echo Area, Next: Invisible Text, 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 displays 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. In batch mode, `message' prints the message text on the standard error stream, followed by a newline. 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 ---------- - Function: message-or-box STRING &rest ARGUMENTS This function displays a message like `message', but may display it in a dialog box instead of the echo area. If this function is called in a command that was invoked using the mouse--more precisely, if `last-nonmenu-event' (*note Command Loop Info::.) is either `nil' or a list--then it uses a dialog box or pop-up menu to display the message. Otherwise, it uses the echo area. (This is the same criterion that `y-or-n-p' uses to make a similar decision; see *Note Yes-or-No Queries::.) You can force use of the mouse or of the echo area by binding `last-nonmenu-event' to a suitable value around the call. - Function: message-box STRING &rest ARGUMENTS This function displays a message like `message', but uses a dialog box (or a pop-up menu) whenever that is possible. If it is impossible to use a dialog box or pop-up menu, because the terminal does not support them, then `message-box' uses the echo area, like `message'. - Function: current-message This function returns the message currently being displayed in the echo area, or `nil' if there is none. - 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. - Variable: echo-area-clear-hook This normal hook is run whenever the echo area is cleared--either by `(message nil)' or for any other reason. Almost all the messages displayed in the echo area are also recorded in the `*Messages*' buffer. - User Option: message-log-max This variable specifies how many lines to keep in the `*Messages*' buffer. The value `t' means there is no limit on how many lines to keep. The value `nil' disables message logging entirely. Here's how to display a message and prevent it from being logged: (let (message-log-max) (message ...)) - Variable: echo-keystrokes This variable determines how much time should elapse before command characters echo. Its value must be an integer, which specifies the number of seconds to wait before echoing. If the user types a prefix key (such as `C-x') and then delays this many seconds before continuing, the prefix key is echoed in the echo area. (Once echoing begins in a key sequence, all subsequent characters in the same key sequence are echoed immediately.) If the value is zero, then command input is not echoed.  File: elisp, Node: Invisible Text, Next: Selective Display, Prev: The Echo Area, Up: Display Invisible Text ============== You can make characters "invisible", so that they do not appear on the screen, with the `invisible' property. This can be either a text property (*note Text Properties::.) or a property of an overlay (*note Overlays::.). In the simplest case, any non-`nil' `invisible' property makes a character invisible. This is the default case--if you don't alter the default value of `buffer-invisibility-spec', this is how the `invisible' property works. More generally, you can use the variable `buffer-invisibility-spec' to control which values of the `invisible' property make text invisible. This permits you to classify the text into different subsets in advance, by giving them different `invisible' values, and subsequently make various subsets visible or invisible by changing the value of `buffer-invisibility-spec'. Controlling visibility with `buffer-invisibility-spec' is especially useful in a program to display the list of entries in a data base. It permits the implementation of convenient filtering commands to view just a part of the entries in the data base. Setting this variable is very fast, much faster than scanning all the text in the buffer looking for properties to change. - Variable: buffer-invisibility-spec This variable specifies which kinds of `invisible' properties actually make a character invisible. `t' A character is invisible if its `invisible' property is non-`nil'. This is the default. a list Each element of the list specifies a criterion for invisibility; if a character's `invisible' property fits any one of these criteria, the character is invisible. The list can have two kinds of elements: `ATOM' A character is invisible if its `invisible' property value is ATOM or if it is a list with ATOM as a member. `(ATOM . t)' A character is invisible if its `invisible' property value is ATOM or if it is a list with ATOM as a member. Moreover, if this character is at the end of a line and is followed by a visible newline, it displays an ellipsis. Two functions are specifically provided for adding elements to `buffer-invisibility-spec' and removing elements from it. - Function: add-to-invisibility-spec ELEMENT Add the element ELEMENT to `buffer-invisibility-spec' (if it is not already present in that list). - Function: remove-from-invisibility-spec ELEMENT Remove the element ELEMENT from `buffer-invisibility-spec'. One convention about the use of `buffer-invisibility-spec' is that a major mode should use the mode's own name as an element of `buffer-invisibility-spec' and as the value of the `invisible' property: ;; If you want to display an ellipsis: (add-to-invisibility-spec '(my-symbol . t)) ;; If you don't want ellipsis: (add-to-invisibility-spec 'my-symbol) (overlay-put (make-overlay beginning end) 'invisible 'my-symbol) ;; When done with the overlays: (remove-from-invisibility-spec '(my-symbol . t)) ;; Or respectively: (remove-from-invisibility-spec 'my-symbol) Ordinarily, commands that operate on text or move point do not care whether the text is invisible. The user-level line motion commands explicitly ignore invisible newlines if `line-move-ignore-invisible' is non-`nil', but only because they are explicitly programmed to do so. Incremental search can make invisible overlays visible temporarily and/or permanently when a match includes invisible text. To enable this, the overlay should have a non-`nil' `isearch-open-invisible' property. The property value should be a function to be called with the overlay as an argument. This function should make the overlay visible permanently; it is used when the match overlaps the overlay on exit from the search. During the search, such overlays are made temporarily visible by temporarily modifying their invisible and intangible properties. If you want this to be done differently for a certain overlay, give it an `isearch-open-invisible-temporary' property which is a function. The function is called with two arguments: the first is the overlay, and the second is `t' to make the overlay visible, or `nil' to make it invisible again.  File: elisp, Node: Selective Display, Next: Overlay Arrow, Prev: Invisible Text, Up: Display Selective Display ================= "Selective display" refers to a pair of related features for hiding certain lines on the screen. The first variant, explicit selective display, is designed for use in a Lisp program: it controls which lines are hidden by altering the text. The invisible text feature (*note Invisible Text::.) has partially replaced this feature. In the second variant, the choice of lines to hide is made automatically based on indentation. This variant is designed to be 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 that 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. This is explicit selective display. * 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 to call attention to a particular line, or `nil' if the arrow feature is not in use. - Variable: overlay-arrow-position This variable holds a marker that indicates where to display the overlay 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 that this marker points into. Thus, only one buffer can have an overlay arrow at any given time. You can do a similar job by creating an overlay with a `before-string' property. *Note Overlay Properties::.  File: elisp, Node: Temporary Displays, Next: Overlays, Prev: Overlay Arrow, Up: Display Temporary Displays ================== Temporary displays are used by Lisp programs to put output into a buffer and then present it to the user for perusal rather than for editing. Many 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 is 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. It is a good idea for this function to run `temp-buffer-show-hook' just as `with-output-to-temp-buffer' normally would, inside of `save-window-excursion' and with the chosen window and buffer selected. - Variable: temp-buffer-show-hook This normal hook is run by `with-output-to-temp-buffer' after displaying the help buffer. When the hook runs, the help buffer is current, and the window it was displayed in is selected. - 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 the string STRING does not contain control characters, you can do the same job in a more general way by creating (and then subsequently deleting) an overlay with a `before-string' property. *Note Overlay Properties::. 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: Width, Prev: Temporary Displays, Up: Display Overlays ======== You can use "overlays" to alter the appearance of a buffer's text on the screen, for the sake of presentation features. An overlay is an object that 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 that the properties that alter how a character is displayed can come from either source. But in most respects they are different. 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 property changes, overlay changes are not recorded in the buffer's undo list. *Note Text Properties::, for comparison. `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. `category' If an overlay has a `category' property, we call it the "category" of the overlay. It should be a symbol. The properties of the symbol serve as defaults for the properties of the overlay. `face' This property controls the way text is displayed--for example, which font and which colors. Its value is a face name or a list of face names. *Note Faces::, for more information. If the property value is a list, elements may also have the form `(foreground-color . COLOR-NAME)' or `(background-color . COLOR-NAME)'. These elements specify just the foreground color or just the background color; therefore, there is no need to create a face for each color that you want to use. `mouse-face' This property is used instead of `face' when the mouse is within the range of the overlay. `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. The hook functions are called both before and after each change. If the functions save the information they receive, and compare notes between calls, they can determine exactly what change has been made in the buffer text. When called before a change, each function receives four arguments: the overlay, `nil', and the beginning and end of the text range to be modified. When called after a change, each function receives five arguments: the overlay, `t', the beginning and end of the text range just modified, and the length of the pre-change text replaced by that range. (For an insertion, the pre-change length is zero; for a deletion, that length is the number of characters deleted, and the post-change beginning and end are equal.) `insert-in-front-hooks' This property's value is a list of functions to be called before and after inserting text right at the beginning of the overlay. The calling conventions are the same as for the `modification-hooks' functions. `insert-behind-hooks' This property's value is a list of functions to be called before and after inserting text right at the end of the overlay. The calling conventions are the same as for the `modification-hooks' functions. `invisible' The `invisible' property can make the text in the overlay invisible, which means that it does not appear on the screen. *Note Invisible Text::, for details. `intangible' The `intangible' property on an overlay works just like the `intangible' text property. *Note Special Properties::, for details. `isearch-open-invisible' This property tells incremental search how to make an invisible overlay visible, permanently, if the final match overlaps it. *Note Invisible Text::. `isearch-open-invisible-temporary' This property tells incremental search how to make an invisible overlay visible, temporarily, during the search. *Note Invisible Text::. `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. The string should contain only characters that display as a single column--control characters, including tabs or newlines, will give strange results. `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. The string should contain only characters that display as a single column--control characters, including tabs or newlines, will give strange results. `evaporate' If this property is non-`nil', the overlay is deleted automatically if it ever becomes empty (i.e., if it spans no characters). `local-map' If this property is non-`nil', it specifies a keymap for a portion of the text. The property's value replaces the buffer's local map, when the character after point is within the overlay. *Note Active Keymaps::. 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 any. If OVERLAY does not record any value for that property, but it does have a `category' property which is a symbol, that symbol's PROP property is used. Otherwise, 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::.  File: elisp, Node: Managing Overlays, Prev: Overlay Properties, Up: Overlays Managing Overlays ----------------- This section describes the functions to create, delete and move overlays, and to examine their contents. - Function: make-overlay START END &optional BUFFER FRONT-ADVANCE REAR-ADVANCE This function creates and returns an overlay that belongs to BUFFER and ranges from START to END. Both START and END must specify buffer positions; they may be integers or markers. If BUFFER is omitted, the overlay is created in the current buffer. The arguments FRONT-ADVANCE and REAR-ADVANCE specify the insertion type for the start of the overlay and for the end of the overlay. *Note Marker Insertion Types::. - Function: overlay-start OVERLAY This function returns the position at which OVERLAY starts, as an integer. - Function: overlay-end OVERLAY This function returns the position at which OVERLAY ends, as an integer. - Function: overlay-buffer OVERLAY This function returns the buffer that OVERLAY belongs to. - Function: delete-overlay OVERLAY This function deletes OVERLAY. The overlay continues to exist as a Lisp object, but ceases to be attached to the buffer it belonged to, and ceases to have any effect on display. A deleted overlay is not permanently useless. You can give it a new buffer position by calling `move-overlay'. - Function: move-overlay OVERLAY START END &optional BUFFER This function moves OVERLAY to BUFFER, and places its bounds at START and END. Both arguments START and END must specify buffer positions; they may be integers or markers. If BUFFER is omitted, the overlay stays in the same buffer. The return value is OVERLAY. This is the only valid way to change the endpoints of an overlay. Do not try modifying the markers in the overlay by hand, as that fails to update other vital data structures and can cause some overlays to be "lost". - Function: overlays-at POS This function returns a list of all the overlays that contain position POS in the current buffer. The list is in no particular order. An overlay contains position POS if it begins at or before POS, and ends after POS. - Function: overlays-in BEG END This function returns a list of the overlays that overlap the region BEG through END. "Overlap" means that at least one character is contained within the overlay and also contained within the specified region; however, empty overlays are included in the result if they are located at BEG or between BEG and END. - Function: next-overlay-change POS This function returns the buffer position of the next beginning or end of an overlay, after POS. - Function: previous-overlay-change POS This function returns the buffer position of the previous beginning or end of an overlay, before POS.  File: elisp, Node: Width, Next: Faces, Prev: Overlays, Up: Display Width ===== Since not all characters have the same width, these functions let you check the width of a character. *Note Primitive Indent::, and *Note Screen Lines::, for related functions. - Function: char-width CHAR This function returns the width in columns of the character CHAR, if it were displayed in the current buffer and the selected window. - Function: string-width STRING This function returns the width in columns of the string STRING, if it were displayed in the current buffer and the selected window. - Function: truncate-string-to-width STRING WIDTH &optional START-COLUMN PADDING This function returns the part of STRING that fits within WIDTH columns, as a new string. If STRING does not reach WIDTH, then the result ends where STRING ends. If one multi-column character in STRING extends across the column WIDTH, that character is not included in the result. Thus, the result can fall short of WIDTH but cannot go beyond it. The optional argument START-COLUMN specifies the starting column. If this is non-`nil', then the first START-COLUMN columns of the string are omitted from the value. If one multi-column character in STRING extends across the column START-COLUMN, that character is not included. The optional argument PADDING, if non-`nil', is a padding character added at the beginning and end of the result string, to extend it to exactly WIDTH columns. The padding character is used at the end of the result if it falls short of WIDTH. It is also used at the beginning of the result if one multi-column character in STRING extends across the column START-COLUMN. (truncate-string-to-width "\tab\t" 12 4) => "ab" (truncate-string-to-width "\tab\t" 12 4 ?\ ) => " ab "  File: elisp, Node: Faces, Next: Blinking, Prev: Width, Up: Display Faces ===== A "face" is a named collection of graphical attributes: font, foreground color, background color, and optional underlining. Faces control the display of text on the screen. Each face has its own "face number", which distinguishes faces at low levels within Emacs. However, for most purposes, you can refer to faces in Lisp programs by their names. - Function: facep OBJECT This function returns `t' if OBJECT is a face name symbol (or if it is a vector of the kind used internally to record face data). It returns `nil' otherwise. Each face name is meaningful for all frames, and by default it has the same meaning in all frames. But you can arrange to give a particular face name a special meaning in one frame if you wish. * Menu: * Standard Faces:: The faces Emacs normally comes with. * Defining Faces:: How to define a face with `defface'. * Merging Faces:: How Emacs decides which face to use for a character. * Face Functions:: How to define and examine faces.  File: elisp, Node: Standard Faces, Next: Defining Faces, Up: Faces Standard Faces -------------- This table lists all the standard faces and their uses. `default' This face is used for ordinary text. `modeline' This face is used for mode lines and menu bars. `region' This face is used for highlighting the region in Transient Mark mode. `secondary-selection' This face is used to show any secondary selection you have made. `highlight' This face is meant to be used for highlighting for various purposes. `underline' This face underlines text. `bold' This face uses a bold font, if possible. It uses the bold variant of the frame's font, if it has one. It's up to you to choose a default font that has a bold variant, if you want to use one. `italic' This face uses the italic variant of the frame's font, if it has one. `bold-italic' This face uses the bold italic variant of the frame's font, if it has one.  File: elisp, Node: Defining Faces, Next: Merging Faces, Prev: Standard Faces, Up: Faces Defining Faces -------------- The way to define a new face is with `defface'. This creates a kind of customization item (*note Customization::.) which the user can customize using the Customization buffer (*note Easy Customization: (emacs)Easy Customization.). - Macro: defface FACE SPEC DOC [KEYWORD VALUE]... Declare FACE as a customizable face that defaults according to SPEC. Do not quote the symbol FACE. The argument DOC specifies the face documentation. When `defface' executes, it defines the face according to SPEC, then uses any customizations that were read from the `.emacs' file to override that specification. The purpose of SPEC is to specify how the face should appear on different kinds of terminals. It should be an alist whose elements have the form `(DISPLAY ATTS)'. The element's CAR, DISPLAY, specifies a class of terminals. The CDR, ATTS, is a list of face attributes and their values; it specifies what the face should look like on that kind of terminal. The possible attributes are defined in the value of `custom-face-attributes'. The DISPLAY part of an element of SPEC determines which frames the element applies to. If more than one element of SPEC matches a given frame, the first matching element is the only one used for that frame. There are two possibilities for DISPLAY: `t' This element of SPEC matches all frames. Therefore, any subsequent elements of SPEC are never used. Normally `t' is used in the last (or only) element of SPEC. a list If DISPLAY is a list, each element should have the form `(CHARACTERISTIC VALUE...)'. Here CHARACTERISTIC specifies a way of classifying frames, and the VALUEs are possible classifications which DISPLAY should apply to. Here are the possible values of CHARACTERISTIC: `type' The kind of window system the frame uses--either `x', `pc' (for the MS-DOS console), `w32' (for MS Windows 9X/NT), or `tty'. `class' What kinds of colors the frame supports--either `color', `grayscale', or `mono'. `background' The kind of background--either `light' or `dark'. If an element of DISPLAY specifies more than one VALUE for a given CHARACTERISTIC, any of those values is acceptable. If DISPLAY has more than one element, each element should specify a different CHARACTERISTIC; then *each* characteristic of the frame must match one of the VALUEs specified for it in DISPLAY. Here's how the standard face `region' could be defined with `defface': (defface region ((((class color) (background dark)) (:background "blue")) (t (:background "gray"))) "Used for displaying the region.") Internally, `defface' uses the symbol property `face-defface-spec' to record the face attributes specified in `defface', `saved-face' for the attributes saved by the user with the customization buffer, and `face-documentation' for the documentation string. - User Option: frame-background-mode This option, if non-`nil', specifies the background type to use for interpreting face definitions. If it is `dark', then Emacs treats all frames as if they had a dark background, regardless of their actual background colors. If it is `light', then Emacs treats all frames as if they had a light background.  File: elisp, Node: Merging Faces, Next: Face Functions, Prev: Defining Faces, Up: Faces Merging Faces for Display ------------------------- Here are all the ways to specify which face to use for display of text: * With defaults. Each frame has a "default face", which is used for all text that doesn't somehow specify another face. (We may change this in a forthcoming Emacs version to serve as a default for all text.) * With text properties. A character may have a `face' property; if so, it is displayed with that face. *Note Special Properties::. If the character has a `mouse-face' property, that is used instead of the `face' property when the mouse is "near enough" to the character. * With overlays. An overlay may have `face' and `mouse-face' properties too; they apply to all the text covered by the overlay. * With a region that is active. In Transient Mark mode, the region is highlighted with a particular face (see `region-face', below). * With special glyphs. Each glyph can specify a particular face number. *Note Glyphs::. If these various sources together specify more than one face for a particular character, Emacs merges the attributes of the various faces specified. The attributes of the faces of special glyphs come first; then comes the face for region highlighting, if appropriate; then come attributes of faces from overlays, followed by those from text properties, and last the default face. When multiple overlays cover one character, an overlay with higher priority overrides those with lower priority. *Note Overlays::. If an attribute such as the font or a color is not specified in any of the above ways, the frame's own font or color is used.  File: elisp, Node: Face Functions, Prev: Merging Faces, Up: Faces Functions for Working with Faces -------------------------------- The attributes a face can specify include the font, the foreground color, the background color, and underlining. The face can also leave these unspecified by giving the value `nil' for them. Here are the primitives for creating and changing faces. - Function: make-face NAME This function defines a new face named NAME, initially with all attributes `nil'. It does nothing if there is already a face named NAME. - Function: face-list This function returns a list of all defined face names. - Function: copy-face OLD-FACE NEW-NAME &optional FRAME NEW-FRAME This function defines the face NEW-NAME as a copy of the existing face named OLD-FACE. It creates the face NEW-NAME if that doesn't already exist. If the optional argument FRAME is given, this function applies only to that frame. Otherwise it applies to each frame individually, copying attributes from OLD-FACE in each frame to NEW-FACE in the same frame. If the optional argument NEW-FRAME is given, then `copy-face' copies the attributes of OLD-FACE in FRAME to NEW-NAME in NEW-FRAME. You can modify the attributes of an existing face with the following functions. If you specify FRAME, they affect just that frame; otherwise, they affect all frames as well as the defaults that apply to new frames. - Function: set-face-foreground FACE COLOR &optional FRAME - Function: set-face-background FACE COLOR &optional FRAME These functions set the foreground (or background, respectively) color of face FACE to COLOR. The argument COLOR should be a string, the name of a color. Certain shades of gray are implemented by stipple patterns on black-and-white screens. - Function: set-face-stipple FACE PATTERN &optional FRAME This function sets the background stipple pattern of face FACE to PATTERN. The argument PATTERN should be the name of a stipple pattern defined by the X server, or `nil' meaning don't use stipple. Normally there is no need to pay attention to stipple patterns, because they are used automatically to handle certain shades of gray. - Function: set-face-font FACE FONT &optional FRAME This function sets the font of face FACE. The argument FONT should be a string, either a valid font name for your system or the name of an Emacs fontset (*note Fontsets::.). Note that if you set the font explicitly, the bold and italic attributes cease to have any effect, because the precise font that you specified is always used. - Function: set-face-bold-p FACE BOLD-P &optional FRAME This function sets the bold attribute of face FACE. Non-`nil' means bold; `nil' means non-bold. - Function: set-face-italic-p FACE ITALIC-P &optional FRAME This function sets the italic attribute of face FACE. Non-`nil' means italic; `nil' means non-italic. - Function: set-face-underline-p FACE UNDERLINE-P &optional FRAME This function sets the underline attribute of face FACE. Non-`nil' means do underline; `nil' means don't. - Function: invert-face FACE &optional FRAME Swap the foreground and background colors of face FACE. If the face doesn't specify both foreground and background, then its foreground and background are set to the default background and foreground, respectively. These functions examine the attributes of a face. If you don't specify FRAME, they refer to the default data for new frames. - Function: face-foreground FACE &optional FRAME - Function: face-background FACE &optional FRAME These functions return the foreground color (or background color, respectively) of face FACE, as a string. - Function: face-stipple FACE &optional FRAME This function returns the name of the background stipple pattern of face FACE, or `nil' if it doesn't have one. - Function: face-font FACE &optional FRAME This function returns the name of the font of face FACE. - Function: face-bold-p FACE &optional FRAME This function returns the bold attribute of face FACE. - Function: face-italic-p FACE &optional FRAME This function returns the italic attribute of face FACE. - Function: face-underline-p FACE &optional FRAME This function returns the underline attribute of face FACE. - Function: face-id FACE This function returns the face number of face FACE. - Function: face-documentation FACE This function returns the documentation string of face FACE, or `nil' if none was specified for it. - Function: face-equal FACE1 FACE2 &optional FRAME This returns `t' if the faces FACE1 and FACE2 have the same attributes for display. - Function: face-differs-from-default-p FACE &optional FRAME This returns `t' if the face FACE displays differently from the default face. A face is considered to be "the same" as the normal face if each attribute is either the same as that of the default face or `nil' (meaning to inherit from the default). - Variable: region-face This variable's value specifies the face number to use to display characters in the region when it is active (in Transient Mark mode only). The face thus specified takes precedence over all faces that come from text properties and overlays, for characters in the region. *Note The Mark::, for more information about Transient Mark mode. Normally, the value is the face number of the face named `region'. - Function: frame-update-face-colors FRAME This function updates the way faces display on FRAME, for a change in FRAME's foreground or background color.