@c This is part of the Emacs manual. @c Copyright (C) 1985, 1986, 1987, 1993, 1994, 1995, 1997, 2000, 2001, @c 2002, 2003, 2004, 2005 Free Software Foundation, Inc. @c See file emacs.texi for copying conditions. @node Display, Search, Registers, Top @chapter Controlling the Display Since only part of a large buffer fits in the window, Emacs tries to show a part that is likely to be interesting. Display-control commands allow you to specify which part of the text you want to see, and how to display it. @menu * Faces:: How to change the display style using faces. * Standard Faces:: Emacs' predefined faces. * Font Lock:: Minor mode for syntactic highlighting using faces. * Highlight Changes:: Using colors to show where you changed the buffer. * Highlight Interactively:: Tell Emacs what text to highlight. * Scrolling:: Moving text up and down in a window. * Horizontal Scrolling:: Moving text left and right in a window. * Fringes:: Enabling or disabling window fringes. * Useless Whitespace:: Showing possibly-spurious trailing whitespace. * Follow Mode:: Follow mode lets two windows scroll as one. * Selective Display:: Hiding lines with lots of indentation. * Optional Mode Line:: Optional mode line display features. * Text Display:: How text characters are normally displayed. * Cursor Display:: Features for displaying the cursor. * Display Custom:: Information on variables for customizing display. @end menu @node Faces @section Using Multiple Typefaces @cindex faces You can specify various styles for displaying text using @dfn{faces}. Each face can specify various @dfn{face attributes}, such as the font family, the height, weight and slant of the characters, the foreground and background color, and underlining or overlining. A face does not have to specify all of these attributes; often it inherits most of them from another face. On a window system, all the Emacs face attributes are meaningful. On a character terminal, only some of them work. Some character terminals support inverse video, bold, and underline attributes; some support colors. Character terminals generally do not support changing the height and width or the font family. The easiest way to use faces is to turn on Font Lock mode. @xref{Font Lock}, for more information about Font Lock mode and syntactic highlighting. You can print out the buffer with the highlighting that appears on your screen using the command @code{ps-print-buffer-with-faces}. @xref{PostScript}. Features which rely on text in multiple faces (such as Font Lock mode) will also work on non-windowed terminals that can display more than one face, whether by colors or underlining and emboldening. This includes the console on GNU/Linux, an @code{xterm} which supports colors, the MS-DOS display (@pxref{MS-DOS}), and the MS-Windows version invoked with the @option{-nw} option. Emacs determines automatically whether the terminal has this capability. You control the appearance of a part of the text in the buffer by specifying the face or faces to use for it. The style of display used for any given character is determined by combining the attributes of all the applicable faces specified for that character. Any attribute that isn't specified by these faces is taken from the @code{default} face, whose attributes reflect the default settings of the frame itself. Enriched mode, the mode for editing formatted text, includes several commands and menus for specifying faces for text in the buffer. @xref{Format Faces}, for how to specify the font for text in the buffer. @xref{Format Colors}, for how to specify the foreground and background color. @cindex face colors, setting @findex set-face-foreground @findex set-face-background To alter the appearance of a face, use the customization buffer. @xref{Face Customization}. You can also use X resources to specify attributes of particular faces (@pxref{Resources}). Alternatively, you can change the foreground and background colors of a specific face with @kbd{M-x set-face-foreground} and @kbd{M-x set-face-background}. These commands prompt in the minibuffer for a face name and a color name, with completion, and then set that face to use the specified color. Changing the colors of the @code{default} face also changes the foreground and background colors on all frames, both existing and those to be created in the future. (You can also set foreground and background colors for the current frame only; see @ref{Frame Parameters}.) Emacs can correctly display variable-width fonts, but Emacs commands that calculate width and indentation do not know how to calculate variable widths. This can sometimes lead to incorrect results when you use variable-width fonts. In particular, indentation commands can give inconsistent results, so we recommend you avoid variable-width fonts for editing program source code. Filling will sometimes make lines too long or too short. We plan to address these issues in future Emacs versions. @node Standard Faces @section Standard Faces @findex list-faces-display To see what faces are currently defined, and what they look like, type @kbd{M-x list-faces-display}. It's possible for a given face to look different in different frames; this command shows the appearance in the frame in which you type it. Here are the standard faces for specifying text appearance: @table @code @item default This face is used for ordinary text that doesn't specify any other face. @item bold This face uses a bold variant of the default font, if it has one. @item italic This face uses an italic variant of the default font, if it has one. @item bold-italic This face uses a bold italic variant of the default font, if it has one. @item underline This face underlines text. @item fixed-pitch The basic fixed-pitch face. @item variable-pitch The basic variable-pitch face. @end table Here's an incomplete list of faces used to highlight parts of the text temporarily for specific purposes. (Many other modes define their own faces for this purpose.) @table @code @item highlight This face is used for highlighting portions of text, in various modes. For example, mouse-sensitive text is highlighted using this face. @item mode-line-highlight Like @code{highlight}, but used for portions of text on mode lines. @item isearch This face is used for highlighting Isearch matches. @item lazy-highlight This face is used for lazy highlighting of Isearch and Query Replace matches other than the current one. @item region This face is used for displaying a selected region (when Transient Mark mode is enabled---see below). @item secondary-selection This face is used for displaying a secondary X selection (@pxref{Secondary Selection}). @item trailing-whitespace The face for highlighting trailing whitespace when @code{show-trailing-whitespace} is non-@code{nil}; see @ref{Useless Whitespace}. @item nobreak-space The face for displaying the character ``nobreak space''. @item escape-glyph The face for highlighting the @samp{\} or @samp{^} that indicates a control character. It's also used when @samp{\} indicates a nobreak space or nobreak (soft) hyphen. @item shadow The basic face for making the text less noticeable than the surrounding ordinary text. Usually this is achieved by using shades of grey in contrast with either black or white default foreground color. @end table @cindex @code{region} face When Transient Mark mode is enabled, the text of the region is highlighted when the mark is active. This uses the face named @code{region}; you can control the style of highlighting by changing the style of this face (@pxref{Face Customization}). @xref{Transient Mark}, for more information about Transient Mark mode and activation and deactivation of the mark. These faces control the appearance of parts of the Emacs frame. They exist as faces to provide a consistent way to customize the appearance of these parts of the frame. @table @code @item mode-line This face is used for the mode line of the currently selected window. By default, it's drawn with shadows for a ``raised'' effect on window systems, and drawn as the inverse of the default face on non-windowed terminals. @item mode-line-inactive Like @code{mode-line}, but used for mode lines of the windows other than the selected one (if @code{mode-line-in-non-selected-windows} is non-@code{nil}). This face inherits from @code{mode-line}, so changes in that face affect mode lines in all windows. @item header-line Similar to @code{mode-line} for a window's header line. Most modes don't use the header line, but the Info mode does. @item vertical-border This face is used for the vertical divider between windows. By default this face inherits from the @code{mode-line-inactive} face on character terminals. On window systems the foreground color of this face is used for the vertical line between windows without scrollbars. @item minibuffer-prompt This face is used for the prompt strings displayed in the minibuffer. @item fringe @cindex fringe The face for the fringes to the left and right of windows on graphic displays. (The fringes are the narrow portions of the Emacs frame between the text area and the window's right and left borders.) @xref{Fringes}. @item scroll-bar This face determines the visual appearance of the scroll bar. @xref{Scroll Bars}. @item border This face determines the color of the frame border. @item cursor This face determines the color of the cursor. @item mouse This face determines the color of the mouse pointer. @item tool-bar This is the basic tool-bar face. No text appears in the tool bar, but the colors of this face affect the appearance of tool bar icons. @xref{Tool Bars}. @item tooltip This face is used for tooltips. @xref{Tooltips}. @item menu @cindex menu bar appearance @cindex @code{menu} face, no effect if customized @cindex customization of @code{menu} face This face determines the colors and font of Emacs's menus. @xref{Menu Bars}. Setting the font of LessTif/Motif menus is currently not supported; attempts to set the font are ignored in this case. Likewise, attempts to customize this face in Emacs built with GTK and in the MS-Windows port are ignored by the respective GUI toolkits; you need to use system-wide styles and options to change the appearance of the menus. @end table @node Font Lock @section Font Lock mode @cindex Font Lock mode @cindex mode, Font Lock @cindex syntax highlighting and coloring Font Lock mode is a minor mode, always local to a particular buffer, which highlights (or ``fontifies'') the buffer contents according to the syntax of the text you are editing. It can recognize comments and strings in most languages; in several languages, it can also recognize and properly highlight various other important constructs---for example, names of functions being defined or reserved keywords. Some special modes, such as Occur mode and Info mode, have completely specialized ways of assigning fonts for Font Lock mode. @findex font-lock-mode @findex turn-on-font-lock The command @kbd{M-x font-lock-mode} turns Font Lock mode on with positive argument, off with negative or zero argument, and toggles the mode when it has no argument. The function @code{turn-on-font-lock} unconditionally enables Font Lock mode. This is useful in mode-hook functions. For example, to enable Font Lock mode whenever you edit a C file, you can do this: @example (add-hook 'c-mode-hook 'turn-on-font-lock) @end example @findex global-font-lock-mode @vindex global-font-lock-mode To turn on Font Lock mode automatically in all modes which support it, customize the variable @code{global-font-lock-mode} using the Customize interface (@pxref{Easy Customization}) or use the function @code{global-font-lock-mode} in your @file{.emacs} file, like this: @example (global-font-lock-mode 1) @end example @noindent You can also specify this using the menu bar Options menu, specifying first Syntax Highlighting and then Save Options. Font Lock mode uses several specifically named faces to do its job, including @code{font-lock-string-face}, @code{font-lock-comment-face}, and others. The easiest way to find them all is to use completion on the face name in @code{set-face-foreground}. To change the colors or the fonts used by Font Lock mode to fontify different parts of text, just change these faces. There are two ways to do it: @itemize @bullet @item Invoke @kbd{M-x set-face-foreground} or @kbd{M-x set-face-background} to change the colors of a particular face used by Font Lock. @xref{Faces}. The command @kbd{M-x list-faces-display} displays all the faces currently known to Emacs, including those used by Font Lock. @item Customize the faces interactively with @kbd{M-x customize-face}, as described in @ref{Face Customization}. @end itemize @vindex font-lock-maximum-decoration The variable @code{font-lock-maximum-decoration} specifies the preferred level of fontification, for modes that provide multiple levels. Level 1 is the least amount of fontification; some modes support levels as high as 3. The normal default is ``as high as possible.'' You can specify an integer, which applies to all modes, or you can specify different numbers for particular major modes; for example, to use level 1 for C/C++ modes, and the default level otherwise, use this: @example (setq font-lock-maximum-decoration '((c-mode . 1) (c++-mode . 1))) @end example @vindex font-lock-maximum-size Fontification can be too slow for large buffers, so you can suppress it. The variable @code{font-lock-maximum-size} specifies a buffer size, beyond which buffer fontification is suppressed. @c @w is used below to prevent a bad page-break. @vindex font-lock-beginning-of-syntax-function @cindex incorrect fontification @cindex parenthesis in column zero and fontification @cindex brace in column zero and fontification Comment and string fontification (or ``syntactic'' fontification) relies on analysis of the syntactic structure of the buffer text. For the sake of speed, some modes, including C mode and Lisp mode, rely on a special convention: an open-parenthesis or open-brace in the leftmost column always defines the @w{beginning} of a defun, and is thus always outside any string or comment. (@xref{Left Margin Paren}.) If you don't follow this convention, Font Lock mode can misfontify the text that follows an open-parenthesis or open-brace in the leftmost column that is inside a string or comment. @cindex slow display during scrolling The variable @code{font-lock-beginning-of-syntax-function} (always buffer-local) specifies how Font Lock mode can find a position guaranteed to be outside any comment or string. In modes which use the leftmost column parenthesis convention, the default value of the variable is @code{beginning-of-defun}---that tells Font Lock mode to use the convention. If you set this variable to @code{nil}, Font Lock no longer relies on the convention. This avoids incorrect results, but the price is that, in some cases, fontification for a changed text must rescan buffer text from the beginning of the buffer. This can considerably slow down redisplay while scrolling, particularly if you are close to the end of a large buffer. @findex font-lock-add-keywords Font Lock highlighting patterns already exist for many modes, but you may want to fontify additional patterns. You can use the function @code{font-lock-add-keywords}, to add your own highlighting patterns for a particular mode. For example, to highlight @samp{FIXME:} words in C comments, use this: @example (font-lock-add-keywords 'c-mode '(("\\<\\(FIXME\\):" 1 font-lock-warning-face t))) @end example @findex font-lock-remove-keywords To remove keywords from the font-lock highlighting patterns, use the function @code{font-lock-remove-keywords}. @xref{Search-based Fontification,,, elisp, The Emacs Lisp Reference Manual}, for documentation of the format of this list. @cindex just-in-time (JIT) font-lock @cindex background syntax highlighting Fontifying large buffers can take a long time. To avoid large delays when a file is visited, Emacs fontifies only the visible portion of a buffer. As you scroll through the buffer, each portion that becomes visible is fontified as soon as it is displayed. The parts of the buffer that are not displayed are fontified ``stealthily,'' in the background, i.e.@: when Emacs is idle. You can control this background fontification, also called @dfn{Just-In-Time} (or @dfn{JIT}) Lock, by customizing variables in the customization group @samp{jit-lock}. @xref{Specific Customization}. @node Highlight Changes @section Highlight Changes Mode @findex highlight-changes-mode Use @kbd{M-x highlight-changes-mode} to enable a minor mode that uses faces (colors, typically) to indicate which parts of the buffer were changed most recently. @node Highlight Interactively @section Interactive Highlighting by Matching @cindex highlighting by matching @cindex interactive highlighting It is sometimes useful to highlight the strings that match a certain regular expression. For example, you might wish to see all the references to a certain variable in a program source file, or highlight certain parts in a voluminous output of some program, or make certain cliches stand out in an article. @findex hi-lock-mode Use the @kbd{M-x hi-lock-mode} command to turn on a minor mode that allows you to specify regular expressions of the text to be highlighted. Hi-lock mode works like Font Lock (@pxref{Font Lock}), except that it lets you specify explicitly what parts of text to highlight. You control Hi-lock mode with these commands: @table @kbd @item C-x w h @var{regexp} @key{RET} @var{face} @key{RET} @kindex C-x w h @findex highlight-regexp Highlight text that matches @var{regexp} using face @var{face} (@code{highlight-regexp}). By using this command more than once, you can highlight various parts of the text in different ways. @item C-x w r @var{regexp} @key{RET} @kindex C-x w r @findex unhighlight-regexp Unhighlight @var{regexp} (@code{unhighlight-regexp}). You must enter one of the regular expressions currently specified for highlighting. (You can use completion, or choose from a menu, to enter one of them conveniently.) @item C-x w l @var{regexp} @key{RET} @var{face} @key{RET} @kindex C-x w l @findex highlight-lines-matching-regexp @cindex lines, highlighting @cindex highlighting lines of text Highlight entire lines containing a match for @var{regexp}, using face @var{face} (@code{highlight-lines-matching-regexp}). @item C-x w b @kindex C-x w b @findex hi-lock-write-interactive-patterns Insert all the current highlighting regexp/face pairs into the buffer at point, with comment delimiters to prevent them from changing your program. This key binding runs the @code{hi-lock-write-interactive-patterns} command. These patterns will be read the next time you visit the file while Hi-lock mode is enabled, or whenever you use the @kbd{M-x hi-lock-find-patterns} command. @item C-x w i @kindex C-x w i @findex hi-lock-find-patterns @vindex hi-lock-exclude-modes Re-read regexp/face pairs in the current buffer (@code{hi-lock-write-interactive-patterns}). The list of pairs is found no matter where in the buffer it may be. This command does nothing if the major mode is a member of the list @code{hi-lock-exclude-modes}. @end table @node Scrolling @section Scrolling If a buffer contains text that is too large to fit entirely within a window that is displaying the buffer, Emacs shows a contiguous portion of the text. The portion shown always contains point. @cindex scrolling @dfn{Scrolling} means moving text up or down in the window so that different parts of the text are visible. Scrolling forward means that text moves up, and new text appears at the bottom. Scrolling backward moves text down and new text appears at the top. Scrolling happens automatically if you move point past the bottom or top of the window. You can also explicitly request scrolling with the commands in this section. @table @kbd @item C-l Clear screen and redisplay, scrolling the selected window to center point vertically within it (@code{recenter}). @item C-v Scroll forward (a windowful or a specified number of lines) (@code{scroll-up}). @item @key{NEXT} @itemx @key{PAGEDOWN} Likewise, scroll forward. @item M-v Scroll backward (@code{scroll-down}). @item @key{PRIOR} @itemx @key{PAGEUP} Likewise, scroll backward. @item @var{arg} C-l Scroll so point is on line @var{arg} (@code{recenter}). @item C-M-l Scroll heuristically to bring useful information onto the screen (@code{reposition-window}). @end table @kindex C-l @findex recenter The most basic scrolling command is @kbd{C-l} (@code{recenter}) with no argument. It scrolls the selected window so that point is halfway down from the top of the window. On a text terminal, it also clears the screen and redisplays all windows. That is useful in case the screen is garbled (@pxref{Screen Garbled}). @kindex C-v @kindex M-v @kindex NEXT @kindex PRIOR @kindex PAGEDOWN @kindex PAGEUP @findex scroll-up @findex scroll-down @vindex next-screen-context-lines To read the buffer a windowful at a time, use @kbd{C-v} (@code{scroll-up}) with no argument. This scrolls forward by nearly the whole window height. The effect is to take the two lines at the bottom of the window and put them at the top, followed by nearly a whole windowful of lines that were not previously visible. If point was in the text that scrolled off the top, it ends up at the new top of the window. @kbd{M-v} (@code{scroll-down}) with no argument scrolls backward in a similar way, also with overlap. The number of lines of overlap across a @kbd{C-v} or @kbd{M-v} is controlled by the variable @code{next-screen-context-lines}; by default, it is 2. The function keys @key{NEXT} and @key{PRIOR}, or @key{PAGEDOWN} and @key{PAGEUP}, are equivalent to @kbd{C-v} and @kbd{M-v}. The commands @kbd{C-v} and @kbd{M-v} with a numeric argument scroll the text in the selected window up or down a few lines. @kbd{C-v} with an argument moves the text and point up, together, that many lines; it brings the same number of new lines into view at the bottom of the window. @kbd{M-v} with numeric argument scrolls the text downward, bringing that many new lines into view at the top of the window. @kbd{C-v} with a negative argument is like @kbd{M-v} and vice versa. The names of scroll commands are based on the direction that the text moves in the window. Thus, the command to scroll forward is called @code{scroll-up} because it moves the text upward on the screen. The keys @key{PAGEDOWN} and @key{PAGEUP} derive their names and customary meanings from a different convention that developed elsewhere; hence the strange result that @key{PAGEDOWN} runs @code{scroll-up}. @vindex scroll-preserve-screen-position Some users like the full-screen scroll commands to keep point at the same screen line. To enable this behavior, set the variable @code{scroll-preserve-screen-position} to a non-@code{nil} value. In this mode, when scrolling shifts point off the screen, or into the scrolling margins, Emacs moves point to keep the same vertical position within the window. This mode is convenient for browsing through a file by scrolling by screenfuls; if you come back to the screen where you started, point goes back to the line where it started. However, this mode is inconvenient when you move to the next screen in order to move point to the text there. Another way to do scrolling is with @kbd{C-l} with a numeric argument. @kbd{C-l} does not clear the screen when given an argument; it only scrolls the selected window. With a positive argument @var{n}, it repositions text to put point @var{n} lines down from the top. An argument of zero puts point on the very top line. Point does not move with respect to the text; rather, the text and point move rigidly on the screen. @kbd{C-l} with a negative argument puts point that many lines from the bottom of the window. For example, @kbd{C-u - 1 C-l} puts point on the bottom line, and @kbd{C-u - 5 C-l} puts it five lines from the bottom. @kbd{C-u C-l} scrolls to put point at the center (vertically) of the selected window. @kindex C-M-l @findex reposition-window The @kbd{C-M-l} command (@code{reposition-window}) scrolls the current window heuristically in a way designed to get useful information onto the screen. For example, in a Lisp file, this command tries to get the entire current defun onto the screen if possible. @vindex scroll-conservatively Scrolling happens automatically when point moves out of the visible portion of the text. Normally, automatic scrolling centers point vertically within the window. However, if you set @code{scroll-conservatively} to a small number @var{n}, then if you move point just a little off the screen---less than @var{n} lines---then Emacs scrolls the text just far enough to bring point back on screen. By default, @code{scroll-conservatively} is 0. @cindex aggressive scrolling @vindex scroll-up-aggressively @vindex scroll-down-aggressively When the window does scroll by a longer distance, you can control how aggressively it scrolls, by setting the variables @code{scroll-up-aggressively} and @code{scroll-down-aggressively}. The value of @code{scroll-up-aggressively} should be either @code{nil}, or a fraction @var{f} between 0 and 1. A fraction specifies where on the screen to put point when scrolling upward. More precisely, when a window scrolls up because point is above the window start, the new start position is chosen to put point @var{f} part of the window height from the top. The larger @var{f}, the more aggressive the scrolling. @code{nil}, which is the default, scrolls to put point at the center. So it is equivalent to .5. Likewise, @code{scroll-down-aggressively} is used for scrolling down. The value, @var{f}, specifies how far point should be placed from the bottom of the window; thus, as with @code{scroll-up-aggressively}, a larger value is more aggressive. @vindex scroll-margin The variable @code{scroll-margin} restricts how close point can come to the top or bottom of a window. Its value is a number of screen lines; if point comes within that many lines of the top or bottom of the window, Emacs recenters the window. By default, @code{scroll-margin} is 0. @node Horizontal Scrolling @section Horizontal Scrolling @cindex horizontal scrolling @dfn{Horizontal scrolling} means shifting all the lines sideways within a window---so that some of the text near the left margin is not displayed at all. When the text in a window is scrolled horizontally, text lines are truncated rather than continued (@pxref{Display Custom}). Whenever a window shows truncated lines, Emacs automatically updates its horizontal scrolling whenever point moves off the left or right edge of the screen. You can also use these commands to do explicit horizontal scrolling. @table @kbd @item C-x < Scroll text in current window to the left (@code{scroll-left}). @item C-x > Scroll to the right (@code{scroll-right}). @end table @kindex C-x < @kindex C-x > @findex scroll-left @findex scroll-right The command @kbd{C-x <} (@code{scroll-left}) scrolls the selected window to the left by @var{n} columns with argument @var{n}. This moves part of the beginning of each line off the left edge of the window. With no argument, it scrolls by almost the full width of the window (two columns less, to be precise). @kbd{C-x >} (@code{scroll-right}) scrolls similarly to the right. The window cannot be scrolled any farther to the right once it is displayed normally (with each line starting at the window's left margin); attempting to do so has no effect. This means that you don't have to calculate the argument precisely for @w{@kbd{C-x >}}; any sufficiently large argument will restore the normal display. If you use those commands to scroll a window horizontally, that sets a lower bound for automatic horizontal scrolling. Automatic scrolling will continue to scroll the window, but never farther to the right than the amount you previously set by @code{scroll-left}. @vindex hscroll-margin The value of the variable @code{hscroll-margin} controls how close to the window's edges point is allowed to get before the window will be automatically scrolled. It is measured in columns. If the value is 5, then moving point within 5 columns of the edge causes horizontal scrolling away from that edge. @vindex hscroll-step The variable @code{hscroll-step} determines how many columns to scroll the window when point gets too close to the edge. If it's zero, horizontal scrolling centers point horizontally within the window. If it's a positive integer, it specifies the number of columns to scroll by. If it's a floating-point number, it specifies the fraction of the window's width to scroll by. The default is zero. @vindex auto-hscroll-mode To disable automatic horizontal scrolling, set the variable @code{auto-hscroll-mode} to @code{nil}. @node Fringes @section Window Fringes @cindex fringes On a graphical display, each Emacs window normally has narrow @dfn{fringes} on the left and right edges. The fringes display indications about the text in the window. The most common use of the fringes is to indicate a continuation line, when one line of text is split into multiple lines on the screen. The left fringe shows a curving arrow for each screen line except the first, indicating that ``this is not the real beginning.'' The right fringe shows a curving arrow for each screen line except the last, indicating that ``this is not the real end.'' The fringes indicate line truncation with short horizontal arrows meaning ``there's more text on this line which is scrolled horizontally out of view;'' clicking the mouse on one of the arrows scrolls the display horizontally in the direction of the arrow. The fringes can also indicate other things, such as empty lines, or where a program you are debugging is executing (@pxref{Debuggers}). @findex set-fringe-style @findex fringe-mode You can enable and disable the fringes for all frames using @kbd{M-x fringe-mode}. To enable and disable the fringes for the selected frame, use @kbd{M-x set-fringe-style}. @node Useless Whitespace @section Useless Whitespace @cindex trailing whitespace @cindex whitespace, trailing @vindex show-trailing-whitespace It is easy to leave unnecessary spaces at the end of a line, or empty lines at the end of a file, without realizing it. In most cases, this @dfn{trailing whitespace} has no effect, but there are special circumstances where it matters. You can make trailing whitespace at the end of a line visible on the screen by setting the buffer-local variable @code{show-trailing-whitespace} to @code{t}. Then Emacs displays trailing whitespace in the face @code{trailing-whitespace}. This feature does not apply when point is at the end of the line containing the whitespace. Strictly speaking, that is ``trailing whitespace'' nonetheless, but displaying it specially in that case looks ugly while you are typing in new text. In this special case, the location of point is enough to show you that the spaces are present. @findex delete-trailing-whitespace To delete all trailing whitespace within the current buffer's accessible portion (@pxref{Narrowing}), type @kbd{M-x delete-trailing-whitespace @key{RET}}. (This command does not remove the form-feed characters.) @vindex indicate-empty-lines @vindex default-indicate-empty-lines @cindex unused lines @cindex fringes, and unused line indication Emacs can indicate unused lines at the end of the window with a small image in the left fringe (@pxref{Fringes}). The image appears for window lines that do not correspond to any buffer text. Blank lines at the end of the buffer then stand out because they do not have this image in the fringe. To enable this feature, set the buffer-local variable @code{indicate-empty-lines} to a non-@code{nil} value. The default value of this variable is controlled by the variable @code{default-indicate-empty-lines}; by setting that variable, you can enable or disable this feature for all new buffers. (This feature currently doesn't work on character terminals.) @node Follow Mode @section Follow Mode @cindex Follow mode @cindex mode, Follow @findex follow-mode @cindex windows, synchronizing @cindex synchronizing windows @dfn{Follow mode} is a minor mode that makes two windows, both showing the same buffer, scroll as a single tall ``virtual window.'' To use Follow mode, go to a frame with just one window, split it into two side-by-side windows using @kbd{C-x 3}, and then type @kbd{M-x follow-mode}. From then on, you can edit the buffer in either of the two windows, or scroll either one; the other window follows it. In Follow mode, if you move point outside the portion visible in one window and into the portion visible in the other window, that selects the other window---again, treating the two as if they were parts of one large window. To turn off Follow mode, type @kbd{M-x follow-mode} a second time. @node Selective Display @section Selective Display @cindex selective display @findex set-selective-display @kindex C-x $ Emacs has the ability to hide lines indented more than a certain number of columns (you specify how many columns). You can use this to get an overview of a part of a program. To hide lines in the current buffer, type @kbd{C-x $} (@code{set-selective-display}) with a numeric argument @var{n}. Then lines with at least @var{n} columns of indentation disappear from the screen. The only indication of their presence is that three dots (@samp{@dots{}}) appear at the end of each visible line that is followed by one or more hidden ones. The commands @kbd{C-n} and @kbd{C-p} move across the hidden lines as if they were not there. The hidden lines are still present in the buffer, and most editing commands see them as usual, so you may find point in the middle of the hidden text. When this happens, the cursor appears at the end of the previous line, after the three dots. If point is at the end of the visible line, before the newline that ends it, the cursor appears before the three dots. To make all lines visible again, type @kbd{C-x $} with no argument. @vindex selective-display-ellipses If you set the variable @code{selective-display-ellipses} to @code{nil}, the three dots do not appear at the end of a line that precedes hidden lines. Then there is no visible indication of the hidden lines. This variable becomes local automatically when set. See also @ref{Outline Mode} for another way to hide part of the text in a buffer. @node Optional Mode Line @section Optional Mode Line Features @cindex buffer size display @cindex display of buffer size @findex size-indication-mode The buffer percentage @var{pos} indicates the percentage of the buffer above the top of the window. You can additionally display the size of the buffer by typing @kbd{M-x size-indication-mode} to turn on Size Indication mode. The size will be displayed immediately following the buffer percentage like this: @example @var{POS} of @var{SIZE} @end example @noindent Here @var{SIZE} is the human readable representation of the number of characters in the buffer, which means that @samp{k} for 10^3, @samp{M} for 10^6, @samp{G} for 10^9, etc., are used to abbreviate. @cindex narrowing, and buffer size display If you have narrowed the buffer (@pxref{Narrowing}), the size of the accessible part of the buffer is shown. @cindex line number display @cindex display of line number @findex line-number-mode The current line number of point appears in the mode line when Line Number mode is enabled. Use the command @kbd{M-x line-number-mode} to turn this mode on and off; normally it is on. The line number appears after the buffer percentage @var{pos}, with the letter @samp{L} to indicate what it is. @xref{Minor Modes}, for more information about minor modes and about how to use this command. @cindex narrowing, and line number display If you have narrowed the buffer (@pxref{Narrowing}), the displayed line number is relative to the accessible portion of the buffer. @vindex line-number-display-limit If the buffer is very large (larger than the value of @code{line-number-display-limit}), then the line number doesn't appear. Emacs doesn't compute the line number when the buffer is large, because that would be too slow. Set it to @code{nil} to remove the limit. @vindex line-number-display-limit-width Line-number computation can also be slow if the lines in the buffer are too long. For this reason, Emacs normally doesn't display line numbers if the average width, in characters, of lines near point is larger than the value of the variable @code{line-number-display-limit-width}. The default value is 200 characters. @cindex Column Number mode @cindex mode, Column Number @findex column-number-mode You can also display the current column number by turning on Column Number mode. It displays the current column number preceded by the letter @samp{C}. Type @kbd{M-x column-number-mode} to toggle this mode. @findex display-time @cindex time (on mode line) Emacs can optionally display the time and system load in all mode lines. To enable this feature, type @kbd{M-x display-time} or customize the option @code{display-time-mode}. The information added to the mode line usually appears after the buffer name, before the mode names and their parentheses. It looks like this: @example @var{hh}:@var{mm}pm @var{l.ll} @end example @noindent @vindex display-time-24hr-format Here @var{hh} and @var{mm} are the hour and minute, followed always by @samp{am} or @samp{pm}. @var{l.ll} is the average number of running processes in the whole system recently. (Some fields may be missing if your operating system cannot support them.) If you prefer time display in 24-hour format, set the variable @code{display-time-24hr-format} to @code{t}. @cindex mail (on mode line) @vindex display-time-use-mail-icon @vindex display-time-mail-face @vindex display-time-mail-file @vindex display-time-mail-directory The word @samp{Mail} appears after the load level if there is mail for you that you have not read yet. On a graphical display you can use an icon instead of @samp{Mail} by customizing @code{display-time-use-mail-icon}; this may save some space on the mode line. You can customize @code{display-time-mail-face} to make the mail indicator prominent. Use @code{display-time-mail-file} to specify the mail file to check, or set @code{display-time-mail-directory} to specify the directory to check for incoming mail (any nonempty regular file in the directory is considered as ``newly arrived mail''). @cindex mode line, 3D appearance @cindex attributes of mode line, changing @cindex non-integral number of lines in a window By default, the mode line is drawn on graphics displays with 3D-style highlighting, like that of a button when it is not being pressed. If you don't like this effect, you can disable the 3D highlighting of the mode line, by customizing the attributes of the @code{mode-line} face in your @file{.emacs} init file, like this: @example (set-face-attribute 'mode-line nil :box nil) @end example @noindent Alternatively, you can turn off the box attribute in your @file{.Xdefaults} file: @example Emacs.mode-line.AttributeBox: off @end example @cindex non-selected windows, mode line appearance By default, the mode line of nonselected windows is displayed in a different face, called @code{mode-line-inactive}. Only the selected window is displayed in the @code{mode-line} face. This helps show which window is selected. When the minibuffer is selected, since it has no mode line, the window from which you activated the minibuffer has its mode line displayed using @code{mode-line}; as a result, ordinary entry to the minibuffer does not change any mode lines. @vindex mode-line-in-non-selected-windows You can disable use of @code{mode-line-inactive} by setting variable @code{mode-line-in-non-selected-windows} to @code{nil}; then all mode lines are displayed in the @code{mode-line} face. @node Text Display @section How Text Is Displayed @cindex characters (in text) @acronym{ASCII} printing characters (octal codes 040 through 0176) in Emacs buffers are displayed with their graphics, as are non-ASCII multibyte printing characters (octal codes above 0400). Some @acronym{ASCII} control characters are displayed in special ways. The newline character (octal code 012) is displayed by starting a new line. The tab character (octal code 011) is displayed by moving to the next tab stop column (normally every 8 columns). Other @acronym{ASCII} control characters are normally displayed as a caret (@samp{^}) followed by the non-control version of the character; thus, control-A is displayed as @samp{^A}. Non-@acronym{ASCII} characters 0200 through 0237 (octal) are displayed with octal escape sequences; thus, character code 0230 (octal) is displayed as @samp{\230}. The display of character codes 0240 through 0377 (octal) may be either as escape sequences or as graphics. They do not normally occur in multibyte buffers, but if they do, they are displayed as Latin-1 graphics. In unibyte mode, if you enable European display they are displayed using their graphics (assuming your terminal supports them), otherwise as escape sequences. @xref{Single-Byte Character Support}. @vindex nobreak-char-display @cindex no-break space, display @cindex no-break hyphen, display @cindex soft hyphen, display Some character sets define ``no-break'' versions of the space and hyphen characters, which are used where a line should not be broken. Emacs normally displays these characters with special faces (respectively, @code{nobreak-space} and @code{escape-glyph}) to distinguish them from ordinary spaces and hyphens. You can turn off this feature by setting the variable @code{nobreak-char-display} to @code{nil}. If you set the variable to any other value, that means to prefix these characters with an escape character. @node Cursor Display @section Displaying the Cursor @findex blink-cursor-mode @vindex blink-cursor-alist @cindex cursor, locating visually @cindex cursor, blinking You can customize the cursor's color, and whether it blinks, using the @code{cursor} Custom group (@pxref{Easy Customization}). On graphical terminals, the command @kbd{M-x blink-cursor-mode} enables or disables the blinking of the cursor. (On text terminals, the terminal itself blinks the cursor, and Emacs has no control over it.) You can control how the cursor appears when it blinks off by setting the variable @code{blink-cursor-alist}. @cindex cursor in non-selected windows @vindex cursor-in-non-selected-windows Normally, the cursor appears in non-selected windows in the ``off'' state, with the same appearance as when the blinking cursor blinks ``off''. For a box cursor, this is a hollow box; for a bar cursor, this is a thinner bar. To turn off cursors in non-selected windows, customize the variable @code{cursor-in-non-selected-windows} and assign it a @code{nil} value. @vindex x-stretch-cursor @cindex wide block cursor On graphical terminals, Emacs can optionally draw the block cursor as wide as the character under the cursor---for example, if the cursor is on a tab character, it would cover the full width occupied by that tab character. To enable this feature, set the variable @code{x-stretch-cursor} to a non-@code{nil} value. @findex hl-line-mode @findex global-hl-line-mode @cindex highlight current line If you find it hard to see the cursor, you might like HL Line mode, a minor mode that highlights the line containing point. Use @kbd{M-x hl-line-mode} to enable or disable it in the current buffer. @kbd{M-x global-hl-line-mode} enables or disables the same mode globally. @node Display Custom @section Customization of Display This section contains information for customization only. Beginning users should skip it. @vindex inverse-video If the variable @code{inverse-video} is non-@code{nil}, Emacs attempts to invert all the lines of the display from what they normally are. @vindex visible-bell If the variable @code{visible-bell} is non-@code{nil}, Emacs attempts to make the whole screen blink when it would normally make an audible bell sound. This variable has no effect if your terminal does not have a way to make the screen blink. @vindex no-redraw-on-reenter On a text terminal, when you reenter Emacs after suspending, Emacs normally clears the screen and redraws the entire display. On some terminals with more than one page of memory, it is possible to arrange the termcap entry so that the @samp{ti} and @samp{te} strings (output to the terminal when Emacs is entered and exited, respectively) switch between pages of memory so as to use one page for Emacs and another page for other output. Then you might want to set the variable @code{no-redraw-on-reenter} non-@code{nil}; this tells Emacs to assume, when resumed, that the screen page it is using still contains what Emacs last wrote there. @vindex echo-keystrokes The variable @code{echo-keystrokes} controls the echoing of multi-character keys; its value is the number of seconds of pause required to cause echoing to start, or zero meaning don't echo at all. @xref{Echo Area}. @vindex ctl-arrow If the variable @code{ctl-arrow} is @code{nil}, all control characters in the buffer are displayed with octal escape sequences, except for newline and tab. Altering the value of @code{ctl-arrow} makes it local to the current buffer; until that time, the default value is in effect. The default is initially @code{t}. @xref{Display Tables,, Display Tables, elisp, The Emacs Lisp Reference Manual}. @vindex tab-width @vindex default-tab-width Normally, a tab character in the buffer is displayed as whitespace which extends to the next display tab stop position, and display tab stops come at intervals equal to eight spaces. The number of spaces per tab is controlled by the variable @code{tab-width}, which is made local by changing it, just like @code{ctl-arrow}. Note that how the tab character in the buffer is displayed has nothing to do with the definition of @key{TAB} as a command. The variable @code{tab-width} must have an integer value between 1 and 1000, inclusive. The variable @code{default-tab-width} controls the default value of this variable for buffers where you have not set it locally. @cindex truncation @cindex line truncation, and fringes As an alternative to continuation, Emacs can display long lines by @dfn{truncation}. This means that all the characters that do not fit in the width of the screen or window do not appear at all. On graphical terminals, a small straight arrow in the fringe indicates truncation at either end of the line. On text terminals, @samp{$} appears in the first column when there is text truncated to the left, and in the last column when there is text truncated to the right. @vindex truncate-lines @findex toggle-truncate-lines Horizontal scrolling automatically causes line truncation (@pxref{Horizontal Scrolling}). You can explicitly enable line truncation for a particular buffer with the command @kbd{M-x toggle-truncate-lines}. This works by locally changing the variable @code{truncate-lines}. If that variable is non-@code{nil}, long lines are truncated; if it is @code{nil}, they are continued onto multiple screen lines. Setting the variable @code{truncate-lines} in any way makes it local to the current buffer; until that time, the default value is in effect. The default value is normally @code{nil}. @c @vindex truncate-partial-width-windows @c Idx entry is in Split Windows. If the variable @code{truncate-partial-width-windows} is non-@code{nil}, it forces truncation rather than continuation in any window less than the full width of the screen or frame, regardless of the value of @code{truncate-lines}. For information about side-by-side windows, see @ref{Split Window}. See also @ref{Display,, Display, elisp, The Emacs Lisp Reference Manual}. @vindex overflow-newline-into-fringe If the variable @code{overflow-newline-into-fringe} is non-@code{nil} on a window system, it specifies that lines which are exactly as wide as the window (not counting the final newline character) shall not be broken into two lines on the display (with just the newline on the second line). Instead, the newline overflows into the right fringe, and the cursor will be displayed in the fringe when positioned on that newline. @vindex indicate-buffer-boundaries On a window system, Emacs may indicate the buffer boundaries in the fringes. The buffer boundaries, i.e. first and last line in the buffer, can be marked with angle bitmaps in the left or right fringe. This can be combined with up and down arrow bitmaps shown at the top and bottom of the left or right fringe if the window can be scrolled in either direction. The buffer-local variable @code{indicate-buffer-boundaries} controls how the buffer boundaries and window scrolling is indicated in the fringes. If the value is @code{left} or @code{right}, both angle and arrow bitmaps are displayed in the left or right fringe, respectively. If value is an alist, each element @code{(@var{indicator} . @var{position})} specifies the position of one of the indicators. The @var{indicator} must be one of @code{top}, @code{bottom}, @code{up}, @code{down}, or @code{t} which specifies the default position for the indicators not present in the alist. The @var{position} is one of @code{left}, @code{right}, or @code{nil} which specifies not to show this indicator. For example, @code{((top . left) (t . right))} places the top angle bitmap in left fringe, the bottom angle bitmap in right fringe, and both arrow bitmaps in right fringe. To show just the angle bitmaps in the left fringe, but no arrow bitmaps, use @code{((top . left) (bottom . left))}. @vindex default-indicate-buffer-boundaries The value of the variable @code{default-indicate-buffer-boundaries} is the default value for @code{indicate-buffer-boundaries} in buffers that do not override it. @vindex baud-rate The variable @anchor{baud-rate}@code{baud-rate} holds 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. On terminals, it affects padding, and decisions about whether to scroll part of the screen or redraw it instead. It also affects the behavior of incremental search. On window-systems, @code{baud-rate} is only used to determine how frequently to look for pending input during display updating. A higher value of @code{baud-rate} means that check for pending input will be done less frequently. You can customize the way any particular character code is displayed by means of a display table. @xref{Display Tables,, Display Tables, elisp, The Emacs Lisp Reference Manual}. @cindex hourglass pointer display @vindex hourglass-delay On a window system, Emacs can optionally display the mouse pointer in a special shape to say that Emacs is busy. To turn this feature on or off, customize the group @code{cursor}. You can also control the amount of time Emacs must remain busy before the busy indicator is displayed, by setting the variable @code{hourglass-delay}. @findex tty-suppress-bold-inverse-default-colors On some text-only terminals, bold face and inverse video together result in text that is hard to read. Call the function @code{tty-suppress-bold-inverse-default-colors} with a non-@code{nil} argument to suppress the effect of bold-face in this case. @ignore arch-tag: 2219f910-2ff0-4521-b059-1bd231a536c4 @end ignore