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This is Info file elisp, produced by Makeinfo-1.52 from the input file elisp.texi. This file documents GNU Emacs Lisp. This is edition 2.0 of the GNU Emacs Lisp Reference Manual, for Emacs Version 19. Published by the Free Software Foundation, 675 Massachusetts Avenue, Cambridge, MA 02139 USA Copyright (C) 1990, 1991, 1992 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. File: elisp, Node: Selective Display, Next: Overlay Arrow, Prev: The Echo Area, Up: Emacs 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 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 space. 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 which make parts of the text visible or invisible. When you write a selectively displayed buffer into a file, all the control-m's are replaced by their original 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 `selective-display' 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, what is shown is the *display* 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: Emacs Display 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 is displayed 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: Emacs 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 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> ---------- Buffer: foo ---------- 20 #<buffer foo> ---------- Buffer: foo ---------- - Variable: temp-buffer-show-function The value of this variable, if non-`nil', is called as a function to display a help buffer. This variable is used by `with-output-to-temp-buffer'. 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 (which is a character offset from the beginning of the buffer). The display remains until the next character is typed. If the next character the user types is CHAR, Emacs ignores it. Otherwise, that character 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', then instructions to type CHAR are displayed there, e.g., `Type RET to continue editing'. 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 ---------- This function works by actually changing the text in the buffer. As a result, if you later undo in this buffer, you will see the message come and go. File: elisp, Node: Overlays, Next: Faces, Prev: Temporary Displays, Up: Emacs 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 which 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, 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. `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 is also temporary. `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. `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. `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. 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 set the value of property PROP recorded in OVERLAY to VALUE. It returns VALUE. File: elisp, Node: Managing Overlays, Prev: Overlay Properties, Up: Overlays Managing Overlays ----------------- - Function: make-overlay START END &optional BUFFER This function creates and returns an overlay which 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 return value is the overlay itself. - Function: overlay-start OVERLAY This function returns the position at which OVERLAY starts. - Function: overlay-end OVERLAY This function returns the position at which OVERLAY ends. - 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 part of the buffer it belonged to, and ceases to have any effect on display. - 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: next-overlays-change POS This function returns the buffer position of the next beginning or end of an overlay, after POS. File: elisp, Node: Faces, Next: Blinking, Prev: Overlays, Up: Emacs 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 id number" which distinguishes faces at low levels within Emacs. However, for most purposes, you can refer to faces in Lisp programs by their names. 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: * Choosing a Face:: How Emacs decides which face to use for a character. * Face Functions:: How to define and examine faces. File: elisp, Node: Choosing a Face, Next: Face Functions, Up: Faces Choosing a Face 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", whose id number is zero, which is used for all text that doesn't somehow specify another face. * With text properties. A character may have a `face' property; if so, it's displayed with that face. 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. *Note Special Properties::. * With overlays. An overlay may have `face' and `mouse-face' properties too; they apply to all the text covered by the overlay. * With special glyphs. Each glyph can specify a particular face id 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 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: Choosing a Face, 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 This function defines a new face named NEW which is a copy of the existing face named OLD. If there is already a face named NEW, then it alters the face to have the same attributes as OLD. If the optional argument FRAME is given, this function applies only to that frame. Otherwise it applies to each frame individually. 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 (respectively, background) color of face FACE to COLOR. The argument COLOR color should be a string, the name of a color. - Function: set-face-font FACE FONT &optional FRAME This function sets the font of face FACE. The argument FONT should be a string. - Function: set-face-underline-p FACE UNDERLINE-P &optional FRAME This function sets the underline attribute of face FACE. - 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 background and foreground of the default face. 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 (respectively, background) color of face FACE. The argument COLOR color should be a string, the name of a color. - Function: face-font FACE &optional FRAME This function returns the name of the font of face FACE. - Function: face-underline-p FACE &optional FRAME This function returns the underline attribute of face FACE. - Function: face-id-number FACE This function returns the id number of face FACE. - 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). File: elisp, Node: Blinking, Next: Inverse Video, Prev: Faces, Up: Emacs Display Blinking ======== This section describes the mechanism by which Emacs shows a matching open parenthesis when the user inserts a close parenthesis. - Variable: blink-paren-function The value of this variable should be a function (of no arguments) to be called whenever a char with close parenthesis syntax is inserted. The value of `blink-paren-function' may be `nil', in which case nothing is done. *Please note:* this variable was named `blink-paren-hook' in older Emacs versions, but since it is not called with the standard convention for hooks, it was renamed to `blink-paren-function' in version 19. - Variable: blink-matching-paren If this variable is `nil', then `blink-matching-open' does nothing. - Variable: blink-matching-paren-distance This variable specifies the maximum distance to scan for a matching parenthesis before giving up. - Function: blink-matching-open This function is the default value of `blink-paren-function'. It assumes that point follows a character with close parenthesis syntax and moves the cursor momentarily to the matching opening character. If that character is not already on the screen, then its context is shown by displaying it in the echo area. To avoid long delays, this function does not search farther than `blink-matching-paren-distance' characters. Here is an example of calling this function explicitly. (defun interactive-blink-matching-open () "Indicate momentarily the start of sexp before point." (interactive) (let ((blink-matching-paren-distance (buffer-size)) (blink-matching-paren t)) (blink-matching-open))) File: elisp, Node: Inverse Video, Next: Usual Display, Prev: Blinking, Up: Emacs Display Inverse Video ============= - User Option: inverse-video This variable controls whether Emacs uses inverse video for all text on the screen. Non-`nil' means yes, `nil' means no. The default is `nil'. - User Option: mode-line-inverse-video This variable controls the use of inverse video for mode lines. If it is non-`nil', then mode lines are displayed in inverse video (or another suitable display mode). Otherwise, mode lines are displayed normal, just like the rest of the screen. The default is `t'. File: elisp, Node: Usual Display, Next: Display Tables, Prev: Inverse Video, Up: Emacs Display Usual Display Conventions ========================= The usual display conventions define how to display each character code. You can override these conventions by setting up a display table (*note Display Tables::.). Here are the usual display conventions: * Character codes 32 through 126 map to glyph codes 32 through 126. Normally this means they display as themselves. * Character code 9 is a horizontal tab. It displays as whitespace up to a position determined by `tab-width'. * Character code 10 is a newline. * All other codes in the range 0 through 31, and code 127, display in one of two ways according to the value of `ctl-arrow'. If it is is non-`nil', these codes map to sequences of two glyphs, where the first glyph is the ASCII code for `^'. Otherwise, these codes map just like the codes in the range 128 to 255. * Character codes 128 through 255 map to sequences of four glyphs, where the first glyph is the ASCII code for `\', and the others are digit characters representing the code in octal. The usual display conventions apply even when there is a display table, for any character whose entry in the active display table is `nil'. Thus, when you set up a display table, you need only specify the the characters for which you want unusual behavior. These variables affect the way certain characters are displayed on the screen. Since they change the number of columns the characters occupy, they also affect the indentation functions. - User Option: ctl-arrow This buffer-local variable controls how control characters are displayed. If it is non-`nil', they are displayed as an uparrow followed by the character: `^A'. If it is `nil', they are displayed as a backslash followed by three octal digits: `\001'. - Variable: default-ctl-arrow The value of this variable is the default value for `ctl-arrow' in buffers that do not override it. This is the same as executing the following expression: (default-value 'ctl-arrow) *Note Default Value::. - User Option: tab-width The value of this variable is the spacing between tab stops used for displaying tab characters in Emacs buffers. The default is 8. Note that this feature is completely independent from the user-settable tab stops used by the command `tab-to-tab-stop'. *Note Indent Tabs::. File: elisp, Node: Display Tables, Next: Beeping, Prev: Usual Display, Up: Emacs Display Display Tables ============== You can use the "display table" feature to control how all 256 possible character codes display on the screen. This is useful for displaying European languages that have letters not in the ASCII character set. The display table maps each character code into a sequence of "glyphs", each glyph being an image that takes up one character position on the screen. You can also define how to display each glyph on your terminal, using the "glyph table". * Menu: * Display Table Format:: What a display table consists of. * Active Display Table:: How Emacs selects a display table to use. * Glyphs:: How to define a glyph, and what glyphs mean. * ISO Latin 1:: How to use display tables to support the ISO Latin 1 character set.