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 and variables allow you to specify which part of the text you want to see, and how to display it.

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.

Scrolling means moving text up or down in the window so that different parts of the text are visible.  Scrolling ``forward'' or ``up'' means that text moves up, and new text appears at the bottom. Scrolling ``backward'' or ``down'' 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 scroll explicitly with these commands:

C-l
     Scroll the selected window so that the current line is the center-most text line; on subsequent consecutive invocations, make the current line the top-most line, the bottom-most line, and so forth in cyclic order; also, maybe redisplay the screen (recenter-top-bottom).

C-v
next
PageDown
     Scroll forward by nearly a full window (scroll-up).

M-v
prior
PageUp
     Scroll backward (scroll-down).

C-M-l
     Scroll heuristically to bring useful information onto the screen (reposition-window).

C-l (recenter-top-bottom) is a basic scrolling command. It recenters the selected window, scrolling it so that the current screen line is exactly in the center of the window, or as close to the center as possible.

Typing C-l twice in a row (C-l C-l) scrolls the window so that point is on the topmost screen line.  Typing a third C-l scrolls the window so that point is on the bottom-most screen line. Each successive C-l cycles through these three screen positions.

You can change the cycling order by customizing the list variable recenter-positions.  Each list element should be the symbol top, middle, or bottom, or a number; an integer number means to move the line to the specified screen line, while a floating-point number between 0.0 and 1.0 specifies a percentage of the screen space from the top.  The default, (middle top bottom), is the cycling order described above.  Furthermore, if you change the variable scroll-margin to a non-zero value N, Emacs always leaves N screen lines between point and the top or bottom of the window (see Auto Scrolling).

You can also supply C-l with a prefix argument.  With a plain prefix argument, C-u C-l, Emacs simply recenters point.  With a positive argument N, it scrolls to place point N lines down from the top of the window.  An argument of zero puts point on the topmost line.  A negative argument -N puts point N lines from the bottom of the window.  For example, C-u - 1 C-l puts point on the bottom line, and C-u - 5 C-l puts it five lines from the bottom.  When given an argument, C-l does not clear the screen or cycle through different screen positions.

The more primitive command recenter behaves like recenter-top-bottom, but does not cycle among screen positions. Prior to Emacs 23, C-l was bound to recenter.

If the variable recenter-redisplay has a non-nil value, Emacs clears and redisplays the screen each time C-l recenters the window; the special value tty (the default) says to do this on text-terminal frames only.  Redisplaying is useful in case the screen becomes garbled for any reason (see Screen Garbled).

To read the buffer a windowful at a time, type C-v (scroll-up).  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 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.

M-v (scroll-down) scrolls backward in a similar way.

The variable next-screen-context-lines controls the number of lines of overlap left by C-v or M-v; by default, it is 2. The function keys next and prior, or PageDown and PageUp, are equivalent to C-v and M-v respectively.

You can supply C-v or M-v with a numeric prefix argument N.  This scrolls the window by N lines, while attempting to leave point unchanged (so that the text and point move up or down together).  C-v with a negative argument is like 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 scroll-up because it moves the text upward on the screen.  The keys PageUp and PageDown derive their names and customary meanings from a different convention that developed elsewhere; hence the strange result that PageDown runs scroll-up.

Some users like the full-screen scroll commands to keep point at the same screen position.  To enable this behavior, set the variable scroll-preserve-screen-position to a non-nil value. Then, whenever a command scrolls the text around point offscreen (or within scroll-margin lines of the edge), Emacs moves point to keep it at the same vertical and horizontal 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.

The C-M-l command (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.

Automatic Scrolling
===================

Emacs performs automatic scrolling when point moves out of the visible portion of the text.

Normally, this centers point vertically within the window.  However, if you set scroll-conservatively to a small number N, then if you move point just a little off the screen (less than N lines), Emacs scrolls the text just far enough to bring point back on screen.  By default, scroll-conservatively is 0.

When the window does scroll by a longer distance, you can control how aggressively it scrolls by setting the variables scroll-up-aggressively and scroll-down-aggressively. The value of scroll-up-aggressively should be either nil, or a fraction F between 0 and 1.  A fraction specifies where on the screen to put point when scrolling upward: when a window scrolls up because point is above the window start, the new start position is chosen to put point F parts of the window height from the top.  Thus, larger F means more aggressive scrolling.  The default value, nil, is equivalent to 0.5.

Likewise, scroll-down-aggressively is used for scrolling down.  The value specifies how far point should be placed from the bottom of the window; thus, as with scroll-up-aggressively, a larger value is more aggressive.

The variable 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 performs automatic scrolling.  By default, scroll-margin is 0.

Horizontal Scrolling
====================

Horizontal scrolling means shifting all the lines sideways within a window, so that some of the text near the left margin is not displayed.  When the text in a window is scrolled horizontally, text lines are truncated rather than continued (see Line Truncation). If a window shows truncated lines, Emacs performs automatic horizontal scrolling whenever point moves off the left or right edge of the screen.  To disable automatic horizontal scrolling, set the variable auto-hscroll-mode to nil.  Note that when the automatic horizontal scrolling is turned off, if point moves off the edge of the screen, the cursor disappears to indicate that.  (On text-mode terminals, the cursor is left at the edge instead.)

The variable hscroll-margin controls how close point can get to the window's edges before automatic scrolling occurs.  It is measured in columns.  For example, if the value is 5, then moving point within 5 columns of an edge causes horizontal scrolling away from that edge.

The variable hscroll-step determines how many columns to scroll the window when point gets too close to the edge.  Zero, the default value, means to center point horizontally within the window. A positive integer value specifies the number of columns to scroll by. A floating-point number specifies the fraction of the window's width to scroll by.

You can also perform explicit horizontal scrolling with the following commands:

C-x <
     Scroll text in current window to the left (scroll-left).

C-x >
     Scroll to the right (scroll-right).

C-x < (scroll-left) scrolls text in the selected window to the left by the full width of the window, less two columns.  (In other words, the text in the window moves left relative to the window.)  With a numeric argument N, it scrolls by N columns.

If the text is scrolled to the left, and point moves off the left edge of the window, the cursor will freeze at the left edge of the window, until point moves back to the displayed portion of the text. This is independent of the current setting of auto-hscroll-mode, which, for text scrolled to the left, only affects the behavior at the right edge of the window.

C-x > (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 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 scroll-left.

Follow Mode
===========

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 C-x 3, and then type 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 M-x follow-mode a second time.

Faces: Controlling Text Display Style
=====================================

Emacs can display text in several different styles, which are called faces.  Each face can specify various face attributes, such as the font, height, weight and slant, 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 text-only terminal, not all face attributes are meaningful. Some text-only terminals support inverse video, bold, and underline attributes; some support colors.  Text-only terminals generally do not support changing the height, width or font.

Most major modes assign faces to the text automatically through the work of Font Lock mode.  See Font Lock, for more information about Font Lock mode and syntactic highlighting.  You can print the current buffer with the highlighting that appears on your screen using the command ps-print-buffer-with-faces.  See PostScript.

Enriched mode, the mode for editing formatted text, provides commands and menus for specifying faces for text in the buffer. See Format Faces.

To alter the appearance of a face, use the customization buffer. See Face Customization.  You can also use X resources to specify attributes of any particular face (see Resources).  When displaying a character, any attribute that isn't specified by its face is taken from the default face, whose attributes reflect the default settings of the frame itself.

You can also change the foreground and background colors of a specific face with M-x set-face-foreground and 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.  See Face Customization, for information about color names.  These commands affect the face colors on all frames, both existing and those to be created in the future.  These changes do not, however, persist for future Emacs sessions; to make lasting changes, use the customization buffer (see Face Customization).

You can also set foreground and background colors for the current frame only; see Frame Parameters.

Emacs can display variable-width fonts, but some of the 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, especially for editing program source code.

Standard Faces
==============

To see what faces are currently defined, and what they look like, type 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.  With a prefix argument, this prompts for a regular expression, and displays only faces with names matching that regular expression.

Here are the standard faces for specifying text appearance.  You can apply them to specific text when you want the effects they produce.

default
     This face is used for ordinary text that doesn't specify any face.

bold
     This face uses a bold variant of the default font.

italic
     This face uses an italic variant of the default font.

bold-italic
     This face uses a bold italic variant of the default font.

underline
     This face underlines text.

fixed-pitch
     This face forces use of a fixed-width font.  It's reasonable to customize this face to use a different fixed-width font, if you like, but you should not make it a variable-width font.

variable-pitch
     This face forces use of a variable-width font.

shadow
     This face is used for making the text less noticeable than the surrounding ordinary text.  Usually this can be achieved by using shades of gray in contrast with either black or white default foreground color.

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.)

highlight
     This face is used for highlighting portions of text, in various modes. For example, mouse-sensitive text is highlighted using this face.

isearch
     This face is used for highlighting the current Isearch match (see Incremental Search).

query-replace
     This face is used for highlighting the current Query Replace match (see Replace).

lazy-highlight
     This face is used for lazy highlighting of Isearch and Query Replace matches other than the current one.

region
     This face is used for displaying a selected region (see Mark).

secondary-selection
     This face is used for displaying a secondary X selection (see Secondary Selection).

trailing-whitespace
     The face for highlighting excess spaces and tabs at the end of a line when show-trailing-whitespace is non-nil; see Useless Whitespace.

nobreak-space
     The face for displaying the character ``nobreak space.''

escape-glyph
     The face for highlighting the \ or ^ that indicates a control character.  It's also used when \ indicates a nobreak space or nobreak (soft) hyphen.

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.

mode-line
     This face is used for the mode line of the currently selected window, and for menu bars when toolkit menus are not used.  By default, it's drawn with shadows for a ``raised'' effect on graphical displays, and drawn as the inverse of the default face on non-windowed terminals.

mode-line-inactive
     Like mode-line, but used for mode lines of the windows other than the selected one (if mode-line-in-non-selected-windows is non-nil).  This face inherits from mode-line, so changes in that face affect mode lines in all windows.

mode-line-highlight
     Like highlight, but used for portions of text on mode lines.

mode-line-buffer-id
     This face is used for buffer identification parts in the mode line.

header-line
     Similar to mode-line for a window's header line, which appears at the top of a window just as the mode line appears at the bottom. Most windows do not have a header line---only some special modes, such Info mode, create one.

vertical-border
     This face is used for the vertical divider between windows. By default this face inherits from the mode-line-inactive face on character terminals.  On graphical displays the foreground color of this face is used for the vertical line between windows without scrollbars.

minibuffer-prompt
     This face is used for the prompt strings displayed in the minibuffer. By default, Emacs automatically adds this face to the value of minibuffer-prompt-properties, which is a list of text properties used to display the prompt text.  (This variable takes effect when you enter the minibuffer.)

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.) See Fringes.

scroll-bar
     This face determines the visual appearance of the scroll bar. See Scroll Bars.

border
     This face determines the color of the frame border.

cursor
     This face determines the color of the cursor.

mouse
     This face determines the color of the mouse pointer.

tool-bar
     This face determines the color of tool bar icons.  See Tool Bars.

tooltip
     This face is used for tooltips.  See Tooltips.

menu
     This face determines the colors and font of Emacs's menus.  See Menu Bars.  This has no effect in Emacs built with GTK and in the MS-Windows/Mac ports; you need to use system-wide styles and options to change the appearance of GTK, Windows, or Mac menus.  Setting the font of LessTif/Motif menus is currently not supported; attempts to set the font are ignored in this case.

Temporary Face Changes
======================

The following commands change the default face within a buffer.

To increase the height of the default face in the current buffer, type C-x C-+ or C-x C-=.  To decrease it, type C-x C--.  To restore the default (global) face height, type C-x C-0.  These keys are all bound to the same command, text-scale-adjust, which looks at the last key typed to determine which action to take.

The final key of these commands may be repeated without the leading C-x.  For instance, C-x C-= C-= C-= increases the face height by three steps.  Each step scales the height of the default face by the value of the variable text-scale-mode-step.  As a special case, an argument of 0 removes any scaling currently active.

The commands text-scale-increase and text-scale-decrease increase or decrease the height of the default face, just like C-x C-+ and C-x C-- respectively. You may find it convenient to bind to these commands, rather than text-scale-adjust.

The command text-scale-set sets the height of the default face in the current buffer to an absolute level specified by its prefix argument.

The above commands automatically enable or disable the minor mode text-scale-mode, depending on whether the current font scaling is other than 1 or not.

To temporarily change the face in the current buffer to a variable-pitch (``proportional'') font, use the command M-x variable-pitch-mode to enable or disable the Variable Pitch minor mode.

Font Lock mode
==============

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 programming languages; in several languages, it can also recognize and properly highlight various other important constructs, such as 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.

Font Lock mode is turned on by default in all modes which support it. You can toggle font-lock for each buffer with the command M-x font-lock-mode.  Using a positive argument unconditionally turns Font Lock mode on, and a negative or zero argument turns it off.

If you do not wish Font Lock mode to be turned on by default, customize the variable global-font-lock-mode using the Customize interface (see Easy Customization), or use the function global-font-lock-mode in your .emacs file, like this:

     (global-font-lock-mode 0)

This variable, like all the variables that control Font Lock mode, take effect whenever fontification is done; that is, potentially at any time.

If you have disabled Global Font Lock mode, you can still enable Font Lock for specific major modes by adding the function turn-on-font-lock to the mode hooks (see Hooks).  For example, to enable Font Lock mode for editing C files, you can do this:

     (add-hook 'c-mode-hook 'turn-on-font-lock)

Font Lock mode uses several specifically named faces to do its job, including font-lock-string-face, font-lock-comment-face, and others.  The easiest way to find them all is to use M-x customize-group RET font-lock-faces RET.  You can then use that customization buffer to customize the appearance of these faces.  See Face Customization.

The variable 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:

     (setq font-lock-maximum-decoration
           '((c-mode . 1) (c++-mode . 1)))

Fontification can be too slow for large buffers, so you can suppress it for buffers above a certain size.  The variable font-lock-maximum-size specifies a buffer size, beyond which buffer fontification is suppressed.

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 Lisp mode, rely on a special convention: an open-parenthesis or open-brace in the leftmost column always defines the beginning of a defun, and is thus always outside any string or comment.  (see 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.

The variable 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 beginning-of-defun---that tells Font Lock mode to use the convention.  If you set this variable to 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.

Font Lock highlighting patterns already exist for many modes, but you may want to fontify additional patterns.  You can use the function font-lock-add-keywords, to add your own highlighting patterns for a particular mode.  For example, to highlight FIXME: words in C comments, use this:

     (add-hook 'c-mode-hook
               (lambda ()
                (font-lock-add-keywords nil
                 '(("\\<\\(FIXME\\):" 1 font-lock-warning-face t)))))

To remove keywords from the font-lock highlighting patterns, use the function font-lock-remove-keywords.  See Search-based Fontification (The Emacs Lisp Reference Manual).

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; this type of Font Lock is called Just-In-Time (or JIT) Lock. You can control how JIT Lock behaves, including telling it to perform fontification while idle, by customizing variables in the customization group jit-lock.  See Specific Customization.

Interactive Highlighting
========================

Highlight Changes mode is a minor mode that highlights the parts of the buffer were changed most recently, by giving that text a different face.  To enable or disable Highlight Changes mode, use M-x highlight-changes-mode.

Hi Lock mode is a minor mode that highlights text that matches regular expressions you specify.  For example, you can use it to highlight all the references to a certain variable in a program source file, highlight certain parts in a voluminous output of some program, or highlight certain names in an article.  To enable or disable Hi Lock mode, use the command M-x hi-lock-mode.  To enable Hi Lock mode for all buffers, use M-x global-hi-lock-mode or place (global-hi-lock-mode 1) in your .emacs file.

Hi Lock mode works like Font Lock mode (see Font Lock), except that you specify explicitly the regular expressions to highlight.  You control them with these commands:

C-x w h REGEXP RET FACE RET
     Highlight text that matches REGEXP using face FACE (highlight-regexp).  The highlighting will remain as long as the buffer is loaded.  For example, to highlight all occurrences of the word ``whim'' using the default face (a yellow background) C-x w h whim RET RET.  Any face can be used for highlighting, Hi Lock provides several of its own and these are pre-loaded into a list of default values.  While being prompted for a face use M-n and M-p to cycle through them.

     You can use this command multiple times, specifying various regular expressions to highlight in different ways.

C-x w r REGEXP RET
     Unhighlight REGEXP (unhighlight-regexp).

     If you invoke this from the menu, you select the expression to unhighlight from a list.  If you invoke this from the keyboard, you use the minibuffer.  It will show the most recently added regular expression; use M-p to show the next older expression and M-n to select the next newer expression.  (You can also type the expression by hand, with completion.)  When the expression you want to unhighlight appears in the minibuffer, press RET to exit the minibuffer and unhighlight it.

C-x w l REGEXP RET FACE RET
     Highlight entire lines containing a match for REGEXP, using face FACE (highlight-lines-matching-regexp).

C-x w b
     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 hi-lock-write-interactive-patterns command.)

     These patterns are extracted from the comments, if appropriate, if you invoke M-x hi-lock-find-patterns, or if you visit the file while Hi Lock mode is enabled (since that runs hi-lock-find-patterns).

C-x w i
     Extract regexp/face pairs from comments in the current buffer (hi-lock-find-patterns).  Thus, you can enter patterns interactively with highlight-regexp, store them into the file with hi-lock-write-interactive-patterns, edit them (perhaps including different faces for different parenthesized parts of the match), and finally use this command (hi-lock-find-patterns) to have Hi Lock highlight the edited patterns.

     The variable hi-lock-file-patterns-policy controls whether Hi Lock mode should automatically extract and highlight patterns found in a file when it is visited.  Its value can be nil (never highlight), ask (query the user), or a function.  If it is a function, hi-lock-find-patterns calls it with the patterns as argument; if the function returns non-nil, the patterns are used.  The default is ask.  Note that patterns are always highlighted if you call hi-lock-find-patterns directly, regardless of the value of this variable.

     Also, hi-lock-find-patterns does nothing if the current major mode's symbol is a member of the list hi-lock-exclude-modes.

Window Fringes
==============

On a graphical display, each Emacs window normally has narrow fringes on the left and right edges.  The fringes are used to display symbols that provide information 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.''  If the line's direction is right-to-left (see Bidirectional Editing), the meaning of the curving arrows in the left and right fringes are swapped.

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 (see Debuggers).

You can enable and disable the fringes for all frames using M-x fringe-mode.  To enable and disable the fringes for the selected frame, use M-x set-fringe-style.

Displaying Boundaries
=====================

On a graphical display, Emacs can indicate the buffer boundaries in the fringes.  It indicates the first line and the last line with angle images in the fringes.  This can be combined with up and down arrow images which say whether it is possible to scroll the window up and down.

The buffer-local variable indicate-buffer-boundaries controls how the buffer boundaries and window scrolling is indicated in the fringes.  If the value is left or right, both angle and arrow bitmaps are displayed in the left or right fringe, respectively.

If value is an alist, each element (INDICATOR . POSITION) specifies the position of one of the indicators. The INDICATOR must be one of top, bottom, up, down, or t which specifies the default position for the indicators not present in the alist. The POSITION is one of left, right, or nil which specifies not to show this indicator.

For example, ((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 ((top .  left) (bottom . left)).

Useless 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 trailing whitespace has no effect, but there are special circumstances where it matters, and it can be a nuisance.

You can make trailing whitespace at the end of a line visible by setting the buffer-local variable show-trailing-whitespace to t.  Then Emacs displays trailing whitespace, using the face 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.

To delete all trailing whitespace within the buffer's accessible portion (see Narrowing), type M-x delete-trailing-whitespace RET.  This command does not remove newline characters.

Emacs can indicate unused lines at the end of the window with a small image in the left fringe (see 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 indicate-empty-lines to a non-nil value.  You can enable or disable this feature for all new buffers by setting the default value of this variable, e.g. (setq-default indicate-empty-lines t);.  (This feature currently doesn't work on text-only terminals.)

Selective Display
=================

Emacs has the ability to hide lines indented more than a given number of columns.  You can use this to get an overview of a part of a program.

To hide lines in the current buffer, type C-x $ (set-selective-display) with a numeric argument N.  Then lines with at least N columns of indentation disappear from the screen.  The only indication of their presence is that three dots (...) appear at the end of each visible line that is followed by one or more hidden ones.

The commands C-n and 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 C-x $ with no argument.

If you set the variable selective-display-ellipses to 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 Outline Mode for another way to hide part of the text in a buffer.

Optional Mode Line Features
===========================

The buffer percentage POS indicates the percentage of the buffer above the top of the window.  You can additionally display the size of the buffer by typing M-x size-indication-mode to turn on Size Indication mode.  The size will be displayed immediately following the buffer percentage like this:

     POS of SIZE

Here SIZE is the human readable representation of the number of characters in the buffer, which means that k for 10^3, M for 10^6, G for 10^9, etc., are used to abbreviate.

The current line number of point appears in the mode line when Line Number mode is enabled.  Use the command M-x line-number-mode to turn this mode on and off; normally it is on.  The line number appears after the buffer percentage POS, with the letter L to indicate what it is.

Similarly, you can display the current column number by turning on Column number mode with M-x column-number-mode.  The column number is indicated by the letter C.  However, when both of these modes are enabled, the line and column numbers are displayed in parentheses, the line number first, rather than with L and C.  For example: (561,2).  See Minor Modes, for more information about minor modes and about how to use these commands.

If you have narrowed the buffer (see Narrowing), the displayed line number is relative to the accessible portion of the buffer. Thus, it isn't suitable as an argument to goto-line.  (Use what-line command to see the line number relative to the whole file.)

If the buffer is very large (larger than the value of line-number-display-limit), Emacs won't compute the line number, because that would be too slow; therefore, the line number won't appear on the mode-line.  To remove this limit, set line-number-display-limit to nil.

Line-number computation can also be slow if the lines in the buffer are too long.  For this reason, Emacs doesn't display line numbers if the average width, in characters, of lines near point is larger than the value of line-number-display-limit-width.  The default value is 200 characters.

Emacs can optionally display the time and system load in all mode lines.  To enable this feature, type M-x display-time or customize the option display-time-mode.  The information added to the mode line looks like this:

     HH:MMpm L.LL

Here HH and MM are the hour and minute, followed always by am or pm.  L.LL is the average number, collected for the last few minutes, of processes in the whole system that were either running or ready to run (i.e. were waiting for an available processor).  (Some fields may be missing if your operating system cannot support them.)  If you prefer time display in 24-hour format, set the variable display-time-24hr-format to t.

The word 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 Mail by customizing display-time-use-mail-icon; this may save some space on the mode line.  You can customize display-time-mail-face to make the mail indicator prominent.  Use display-time-mail-file to specify the mail file to check, or set 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'').

When running Emacs on a laptop computer, you can display the battery charge on the mode-line, by using the command display-battery-mode or customizing the variable display-battery-mode.  The variable battery-mode-line-format determines the way the battery charge is displayed; the exact mode-line message depends on the operating system, and it usually shows the current battery charge as a percentage of the total charge.

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 mode-line face.  See Face Customization.

By default, the mode line of nonselected windows is displayed in a different face, called mode-line-inactive.  Only the selected window is displayed in the 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 mode-line; as a result, ordinary entry to the minibuffer does not change any mode lines.

You can disable use of mode-line-inactive by setting variable mode-line-in-non-selected-windows to nil; then all mode lines are displayed in the mode-line face.

You can customize the mode line display for each of the end-of-line formats by setting each of the variables eol-mnemonic-unix, eol-mnemonic-dos, eol-mnemonic-mac, and eol-mnemonic-undecided to the strings you prefer.

How Text Is Displayed
=====================

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 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).  The number of spaces per tab is controlled by the variable tab-width, which must have an integer value between 1 and 1000, inclusive, and is made buffer-local by changing it.  Note that how the tab character in the buffer is displayed has nothing to do with the definition of TAB as a command.

Other ASCII control characters are normally displayed as a caret (^) followed by the non-control version of the character; thus, control-A is displayed as ^A.  The caret appears in face escape-glyph.

Non-ASCII characters 0200 through 0237 (octal) are displayed with octal escape sequences; thus, character code 0230 (octal) is displayed as \230.  The backslash appears in face escape-glyph.

If the variable ctl-arrow is nil, control characters in the buffer are displayed with octal escape sequences, except for newline and tab.  Altering the value of ctl-arrow makes it local to the current buffer; until that time, the default value is in effect.  The default is initially t.

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.  See Unibyte Mode.

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, nobreak-space and escape-glyph) to distinguish them from ordinary spaces and hyphens.  You can turn off this feature by setting the variable nobreak-char-display to nil.  If you set the variable to any other value, that means to prefix these characters with an escape character.

You can customize the way any particular character code is displayed by means of a display table.  See Display Tables (The Emacs Lisp Reference Manual).

On graphics displays, some characters could have no glyphs in any of the fonts available to Emacs.  On text terminals, some characters could be impossible to encode with the terminal coding system (see Terminal Coding).  Emacs can display such glyphless characters using one of the following methods:

zero-width
     Don't display the character.

thin-space
     Display a thin space, 1-pixel wide on graphics displays or 1-character wide on text terminals.

empty-box
     Display an empty box.

acronym
     Display the acronym of the character's name (such as ZWNJ or RLM) in a box.

hex-code
     Display the Unicode codepoint of the character in hexadecimal notation, in a box.

With the exception of zero-width, all other methods draw these characters in a special face glyphless-char, which you can customize.

To control what glyphless characters are displayed using which method, customize the variable glyphless-char-display-control; see its doc string for the details.  For even finer control, set the elements of 2 char-tables: glyphless-char-display and char-acronym-table.

Displaying the Cursor
=====================

You can customize the cursor's color, and whether it blinks, using the cursor Custom group (see Easy Customization).  On a graphical display, the command 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 blink-cursor-alist.

Some text terminals offer two different cursors: the normal cursor and the very visible cursor, where the latter may be e.g. bigger or blinking.  By default Emacs uses the very visible cursor, and switches to it when you start or resume Emacs.  If the variable visible-cursor is nil when Emacs starts or resumes, it doesn't switch, so it uses the normal cursor.

Normally, the cursor appears in non-selected windows without blinking, 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 cursor-in-non-selected-windows and assign it a nil value.

On graphical displays, 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 x-stretch-cursor to a non-nil value.

To make the cursor even more visible, you can use HL Line mode, a minor mode that highlights the line containing point.  Use M-x hl-line-mode to enable or disable it in the current buffer.  M-x global-hl-line-mode enables or disables the same mode globally.

Truncation of Lines
===================

As an alternative to continuation (see Continuation Lines), Emacs can display long lines by 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 displays, a small straight arrow in the fringe indicates truncation at either end of the line.  On text-only terminals, $ appears in the leftmost column when there is text truncated to the left, and in the rightmost column when there is text truncated to the right.

Horizontal scrolling automatically causes line truncation (see Horizontal Scrolling).  You can explicitly enable line truncation for a particular buffer with the command M-x toggle-truncate-lines.  This works by locally changing the variable truncate-lines.  If that variable is non-nil, long lines are truncated; if it is nil, they are continued onto multiple screen lines.  Setting the variable 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 nil.

If the variable truncate-partial-width-windows is non-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 truncate-lines.  See also Display (The Emacs Lisp Reference Manual).

If the variable overflow-newline-into-fringe is non-nil on a graphical display, then Emacs does not continue or truncate a line which is exactly as wide as the window.  Instead, the newline overflows into the right fringe, and the cursor appears in the fringe when positioned on that newline.

Visual Line Mode
================

Another alternative to ordinary line continuation is to use word wrap.  Here, each long logical line is divided into two or more screen lines, like in ordinary line continuation.  However, Emacs attempts to wrap the line at word boundaries near the right window edge.  This makes the text easier to read, as wrapping does not occur in the middle of words.

Word wrap is enabled by Visual Line mode, an optional minor mode. To turn on Visual Line mode in the current buffer, type M-x visual-line-mode; repeating this command turns it off.  You can also turn on Visual Line mode using the menu bar: in the Options menu, select the Line Wrapping in this Buffer submenu, followed by the Word Wrap (Visual Line Mode) menu item.  While Visual Line mode is enabled, the mode-line shows the string wrap in the mode display.  The command M-x global-visual-line-mode toggles Visual Line mode in all buffers.

In Visual Line mode, some editing commands work on screen lines instead of logical lines: C-a (beginning-of-visual-line) moves to the beginning of the screen line, C-e (end-of-visual-line) moves to the end of the screen line, and C-k (kill-visual-line) kills text to the end of the screen line.

To move by logical lines, use the commands M-x next-logical-line and M-x previous-logical-line.  These move point to the next logical line and the previous logical line respectively, regardless of whether Visual Line mode is enabled.  If you use these commands frequently, it may be convenient to assign key bindings to them.  See Init Rebinding.

By default, word-wrapped lines do not display fringe indicators. Visual Line mode is often used to edit files that contain many long logical lines, so having a fringe indicator for each wrapped line would be visually distracting.  You can change this by customizing the variable visual-line-fringe-indicators.

Customization of Display
========================

This section describes variables (see Variables) that you can change to customize how Emacs displays.  Beginning users can skip it.

If the variable visible-bell is non-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.

The variable 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.  The value takes effect when there is someting to echo.  See Echo Area.

The variable baud-rate holds the output speed of the terminal.  Setting this variable does not change the speed of actual data transmission, but the value is used for calculations.  On text-only 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 graphical displays, baud-rate is only used to determine how frequently to look for pending input during display updating.  A higher value of baud-rate means that check for pending input will be done less frequently.

On graphical displays, Emacs displays the mouse pointer as an hourglass if Emacs is busy.  To disable this feature, set the variable display-hourglass to nil.  The variable hourglass-delay determines the number of seconds of ``busy time'' before the hourglass is shown; the default is 1.

If the mouse pointer lies inside an Emacs frame, Emacs makes it invisible each time you type a character to insert text, to prevent it from obscuring the text.  (To be precise, the hiding occurs when you type a ``self-inserting'' character.  See Inserting Text.)  Moving the mouse pointer makes it visible again.  To disable this feature, set the variable make-pointer-invisible to nil.

On graphical displays, the variable underline-minimum-offset determines the minimum distance between the baseline and underline, in pixels, for underlined text.  By default, the value is 1; increasing it may improve the legibility of underlined text for certain fonts. (However, Emacs will never draw the underline below the current line area.)  The variable x-underline-at-descent-line determines how to draw underlined text.  The default is nil, which means to draw it at the baseline level of the font; if you change it to nil, Emacs draws the underline at the same height as the font's descent line.

The variable overline-margin specifies the vertical position of an overline above the text, including the height of the overline itself, in pixels; the default is 2.

On some text-only terminals, bold face and inverse video together result in text that is hard to read.  Call the function tty-suppress-bold-inverse-default-colors with a non-nil argument to suppress the effect of bold-face in this case.

On a text-only 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 ti and 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.  On such terminals, you might want to set the variable no-redraw-on-reenter non-nil; this tells Emacs to assume, when resumed, that the screen page it is using still contains what Emacs last wrote there.