Controlling the Display
***********************

Since only part of a large buffer fits in the window, Emacs has to show only a part of it.  This chapter describes commands and variables that let you specify which part of the text you want to see, and how the text is displayed.

Scrolling
=========

If a window is too small to display all the text in its buffer, it displays only a portion of it.  Scrolling commands change which portion of the buffer is displayed.

Scrolling ``forward'' or ``up'' advances the portion of the buffer displayed in the window; equivalently, it moves the buffer text upwards relative to the window.  Scrolling ``backward'' or ``down'' displays an earlier portion of the buffer, and moves the text downwards relative to the window.

In Emacs, scrolling ``up'' or ``down'' refers to the direction that the text moves in the window, not the direction that the window moves relative to the text.  This terminology was adopted by Emacs before the modern meaning of ``scrolling up'' and ``scrolling down'' became widespread.  Hence, the strange result that PageDown scrolls ``up'' in the Emacs sense.

The portion of a buffer displayed in a window always contains point. If you move point past the bottom or top of the window, scrolling occurs automatically to bring it back onscreen (see Auto Scrolling).  You can also scroll explicitly with these commands:

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

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

C-v (scroll-up-command) 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 on the window's new topmost line.  The next (or PageDown) key is equivalent to C-v.

M-v (scroll-down-command) scrolls backward in a similar way.  The prior (or PageUp) key is equivalent to M-v.

The number of lines of overlap left by these scroll commands is controlled by the variable next-screen-context-lines, whose default value is 2.  You can supply the commands with a numeric prefix argument, N, to scroll by N lines; Emacs attempts 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.

By default, these commands signal an error (by beeping or flashing the screen) if no more scrolling is possible, because the window has reached the beginning or end of the buffer.  If you change the variable scroll-error-top-bottom to t, the command moves point to the farthest possible position.  If point is already there, the command signals an error.

Some users like scroll commands to keep point at the same screen position, so that scrolling back to the same screen conveniently returns point to its original position.  You can enable this behavior via the variable scroll-preserve-screen-position.  If the value is t, Emacs adjusts point to keep the cursor at the same screen position whenever a scroll command moves it off-window, rather than moving it to the topmost or bottommost line.  With any other non-nil value, Emacs adjusts point this way even if the scroll command leaves point in the window.  This variable affects all the scroll commands documented in this section, as well as scrolling with the mouse wheel (see Mouse Commands); in general, it affects any command that has a non-nil scroll-command property. See Property Lists (The Emacs Lisp Reference Manual).

The commands M-x scroll-up and M-x scroll-down behave similarly to scroll-up-command and scroll-down-command, except they do not obey scroll-error-top-bottom.  Prior to Emacs 24, these were the default commands for scrolling up and down. The commands M-x scroll-up-line and M-x scroll-down-line scroll the current window by one line at a time.  If you intend to use any of these commands, you might want to give them key bindings (see Init Rebinding).

Recentering
===========

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

M-x recenter
     Scroll the selected window so the current line is the center-most text line.  Possibly redisplay the screen too.

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

The C-l (recenter-top-bottom) command 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 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 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 of the window.  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, C-l always leaves at least N screen lines between point and the top or bottom of the window (see Auto Scrolling).

You can also give C-l a prefix argument.  A plain prefix argument, C-u C-l, simply recenters point.  A positive argument N puts 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.  When given an argument, C-l does not clear the screen or cycle through different screen positions.

If the variable recenter-redisplay has a non-nil value, each invocation of C-l also clears and redisplays the screen; 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).

The more primitive command M-x recenter behaves like recenter-top-bottom, but does not cycle among screen positions.

C-M-l (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.  If you set scroll-conservatively to a large number (larger than 100), Emacs will never center point as result of scrolling, even if point moves far away from the text previously displayed in the window.  With such a large value, Emacs will always scroll text just enough for bringing point into view, so point will end up at the top or bottom of the window, depending on the scroll direction.

The variable scroll-step determines how many lines to scroll the window when point moves off the screen.  If moving by that number of lines fails to bring point back into view, point is centered instead.  The default value is zero, which causes point to always be centered after scrolling.

When the window does scroll by a distance longer than scroll-step, 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, i.e. forward.  When point goes off the window end, the new start position is chosen to put point F parts of the window height from the bottom margin.  Thus, larger F means more aggressive scrolling: more new text is brought into view.  The default value, nil, is equivalent to 0.5.

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

These two variables are ignored if either scroll-step or scroll-conservatively are set to a non-zero value.

The variable scroll-margin restricts how close point can come to the top or bottom of a window (even if aggressive scrolling specifies a fraction F that is larger than the window portion between the top and the bottom margins).  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 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.

Narrowing
=========

Narrowing means focusing in on some portion of the buffer, making the rest temporarily inaccessible.  The portion which you can still get to is called the accessible portion.  Canceling the narrowing, which makes the entire buffer once again accessible, is called widening.  The bounds of narrowing in effect in a buffer are called the buffer's restriction.

Narrowing can make it easier to concentrate on a single subroutine or paragraph by eliminating clutter.  It can also be used to limit the range of operation of a replace command or repeating keyboard macro.

C-x n n
     Narrow down to between point and mark (narrow-to-region).

C-x n w
     Widen to make the entire buffer accessible again (widen).

C-x n p
     Narrow down to the current page (narrow-to-page).

C-x n d
     Narrow down to the current defun (narrow-to-defun).

When you have narrowed down to a part of the buffer, that part appears to be all there is.  You can't see the rest, you can't move into it (motion commands won't go outside the accessible part), you can't change it in any way.  However, it is not gone, and if you save the file all the inaccessible text will be saved.  The word Narrow appears in the mode line whenever narrowing is in effect.

The primary narrowing command is C-x n n (narrow-to-region). It sets the current buffer's restrictions so that the text in the current region remains accessible, but all text before the region or after the region is inaccessible.  Point and mark do not change.

Alternatively, use C-x n p (narrow-to-page) to narrow down to the current page.  See Pages, for the definition of a page. C-x n d (narrow-to-defun) narrows down to the defun containing point (see Defuns).

The way to cancel narrowing is to widen with C-x n w (widen).  This makes all text in the buffer accessible again.

You can get information on what part of the buffer you are narrowed down to using the C-x = command.  See Position Info.

Because narrowing can easily confuse users who do not understand it, narrow-to-region is normally a disabled command.  Attempting to use this command asks for confirmation and gives you the option of enabling it; if you enable the command, confirmation will no longer be required for it.  See Disabling.

View Mode
=========

View mode is a minor mode that lets you scan a buffer by sequential screenfuls.  It provides commands for scrolling through the buffer conveniently but not for changing it.  Apart from the usual Emacs cursor motion commands, you can type SPC to scroll forward one windowful, DEL to scroll backward, and s to start an incremental search.

Typing q (View-quit) disables View mode, and switches back to the buffer and position before View mode was enabled.  Typing e (View-exit) disables View mode, keeping the current buffer and position.

M-x view-buffer prompts for an existing Emacs buffer, switches to it, and enables View mode.  M-x view-file prompts for a file and visits it with View mode enabled.

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.

Text Faces
==========

Emacs can display text in several different styles, called faces.  Each face can specify various face attributes, such as the font, height, weight, slant, foreground and background color, and underlining or overlining.  Most major modes assign faces to the text automatically, via Font Lock mode.  See Font Lock, for more information about how these faces are assigned.

To see what faces are currently defined, and what they look like, type M-x list-faces-display.  With a prefix argument, this prompts for a regular expression, and displays only faces with names matching that regular expression (see Regexps).

It's possible for a given face to look different in different frames.  For instance, some text terminals do not support all face attributes, particularly font, height, and width, and some support a limited range of colors.  In addition, most Emacs faces are defined so that their attributes are different on light and dark frame backgrounds, for reasons of legibility.  By default, Emacs automatically chooses which set of face attributes to display on each frame, based on the frame's current background color.  However, you can override this by giving the variable frame-background-mode a non-nil value.  A value of dark makes Emacs treat all frames as if they have a dark background, whereas a value of light makes it treat all frames as if they have a light background.

You can customize a face to alter its attributes, and save those customizations for future Emacs sessions.  See Face Customization, for details.

The default face is the default for displaying text, and all of its attributes are specified.  Its background color is also used as the frame's background color.  See Colors.

Another special face is the cursor face.  On graphical displays, the background color of this face is used to draw the text cursor.  None of the other attributes of this face have any effect; the foreground color for text under the cursor is taken from the background color of the underlying text.  On text terminals, the appearance of the text cursor is determined by the terminal, not by the cursor face.

You can also use X resources to specify attributes of any particular face.  See Resources.

Emacs can display variable-width fonts, but some Emacs commands, particularly indentation commands, do not account for variable character display widths.  Therefore, we recommend not using variable-width fonts for most faces, particularly those assigned by Font Lock mode.

Colors for Faces
================

Faces can have various foreground and background colors.  When you specify a color for a face---for instance, when customizing the face (see Face Customization)---you can use either a color name or an RGB triplet.

A color name is a pre-defined name, such as dark orange or medium sea green.  To view a list of color names, type M-x list-colors-display.  To control the order in which colors are shown, customize list-colors-sort.  If you run this command on a graphical display, it shows the full range of color names known to Emacs (these are the standard X11 color names, defined in X's rgb.txt file).  If you run the command on a text terminal, it shows only a small subset of colors that can be safely displayed on such terminals.  However, Emacs understands X11 color names even on text terminals; if a face is given a color specified by an X11 color name, it is displayed using the closest-matching terminal color.

An RGB triplet is a string of the form #RRGGBB.  Each of the R, G, and B components is a hexadecimal number specifying the component's relative intensity, one to four digits long (usually two digits are used).  The components must have the same number of digits. For hexadecimal values A to F, either upper or lower case are acceptable.

The M-x list-colors-display command also shows the equivalent RGB triplet for each named color.  For instance, medium sea green is equivalent to #3CB371.

You can change the foreground and background colors of a 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, with completion, and then set that face to use the specified color. They affect the face colors on all frames, but their effects do not persist for future Emacs sessions, unlike using the customization buffer or X resources.  You can also use frame parameters to set foreground and background colors for a specific frame; see Frame Parameters.

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

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. Its background color is used as the frame's background color.

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 text highlighting in various contexts, such as when the mouse cursor is moved over a hyperlink.

isearch
     This face is used to highlight the current Isearch match (see Incremental Search).

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

lazy-highlight
     This face is used to highlight ``lazy matches'' for Isearch and Query Replace (matches other than the current one).

region
     This face is used for displaying an active region (see Mark). When Emacs is built with GTK support, its colors are taken from the current GTK theme.

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).

escape-glyph
     The face for displaying control characters and escape sequences (see Text Display).

nobreak-space
     The face for displaying ``no-break'' space characters (see Text Display).

The following faces control the appearance of parts of the Emacs 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 on text terminals.

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.

cursor
     The :background attribute of this face specifies the color of the text cursor.  See Cursor Display.

tooltip
     This face is used for tooltip text.  By default, if Emacs is built with GTK support, tooltips are drawn via GTK and this face has no effect.  See Tooltips.

mouse
     This face determines the color of the mouse pointer.

The following faces likewise control the appearance of parts of the Emacs frame, but only on text terminals, or when Emacs is built on X with no toolkit support.  (For all other cases, the appearance of the respective frame elements is determined by system-wide settings.)

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

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

menu
     This face determines the colors and font of Emacs's menus.  See Menu Bars.

Text Scale
==========

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 text height by a factor of 1.2; to change this factor, customize the variable text-scale-mode-step.  As an exception, a numeric argument of 0 to the text-scale-adjust command restores the default height, similar to typing C-x C-0.

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 scales the height of the default face in the current buffer to an absolute level specified by its prefix argument.

The above commands automatically enable the minor mode text-scale-mode if the current font scaling is other than 1, and disable it otherwise.

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

Font Lock mode is a minor mode, always local to a particular buffer, which assigns faces to (or fontifies) the text in the buffer. Each buffer's major mode tells Font Lock mode which text to fontify; for instance, programming language modes fontify syntactically relevant constructs like comments, strings, and function names.

Font Lock mode is enabled by default.  To toggle it in the current buffer, type M-x font-lock-mode.  A positive numeric argument unconditionally enables Font Lock mode, and a negative or zero argument disables it.

Type M-x global-font-lock-mode to toggle Font Lock mode in all buffers.  To impose this setting for future Emacs sessions, customize the variable global-font-lock-mode (see Easy Customization), or add the following line to your init file:

     (global-font-lock-mode 0)

If you have disabled Global Font Lock mode, you can still enable Font Lock for specific major modes by adding the function font-lock-mode 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 'font-lock-mode)

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.

You can customize the variable font-lock-maximum-decoration to alter the amount of fontification applied by Font Lock mode, for major modes that support this feature.  The value should be a number (with 1 representing a minimal amount of fontification; some modes support levels as high as 3); or t, meaning ``as high as possible'' (the default).  You can also specify different numbers for particular major modes; for example, to use level 1 for C/C++ modes, and the default level otherwise, use the value

     '((c-mode . 1) (c++-mode . 1)))

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.  Therefore, you should avoid placing an open-parenthesis or open-brace in the leftmost column, if it is inside a string or comment.  See Left Margin Paren, for details.

The variable font-lock-beginning-of-syntax-function, which is 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 most 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 initially 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 that 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 graphical displays, 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. You can type M-x fringe-mode to disable the fringes, or modify their width.  This command affects fringes in all frames; to modify fringes on the selected frame only, use M-x set-fringe-style.

The most common use of the fringes is to indicate a continuation line (see Continuation Lines).  When one line of text is split into multiple screen lines, 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 meanings of the curving arrows in the 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 buffer boundaries (see Displaying Boundaries), and where a program you are debugging is executing (see Debuggers).

The fringe is also used for drawing the cursor, if the current line is exactly as wide as the window and point is at the end of the line. To disable this, change the variable overflow-newline-into-fringe to nil; this causes Emacs to continue or truncate lines that are exactly as wide as the window.

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

On graphical displays, Emacs can indicate the buffer boundaries in the fringes.  If you enable this feature, the first line and the last line are marked 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.

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 buffer, without realizing it.  In most cases, this trailing whitespace has no effect, but sometimes 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.

Type M-x delete-trailing-whitespace to delete all trailing whitespace.  This command deletes all extra spaces at the end of each line in the buffer, and all empty lines at the end of the buffer; to ignore the latter, change the variable delete-trailing-lines to nil.  If the region is active, the command instead deletes extra spaces at the end of each line in the region.

On graphical displays, 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 screen lines that do not correspond to any buffer text, so blank lines at the end of the buffer stand out because they lack this image.  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).

Whitespace mode is a buffer-local minor mode that lets you ``visualize'' many kinds of whitespace in the buffer, by either drawing the whitespace characters with a special face or displaying them as special glyphs.  To toggle this mode, type M-x whitespace-mode.  The kinds of whitespace visualized are determined by the list variable whitespace-style.  Here is a partial list of possible elements (see the variable's documentation for the full list):

face
     Enable all visualizations which use special faces.  This element has a special meaning: if it is absent from the list, none of the other visualizations take effect except space-mark, tab-mark, and newline-mark.

trailing
     Highlight trailing whitespace.

tabs
     Highlight tab characters.

spaces
     Highlight space and non-breaking space characters.

lines
     Highlight lines longer than 80 lines.  To change the column limit, customize the variable whitespace-line-column.

newline
     Highlight newlines.

empty
     Highlight empty lines.

space-mark
     Draw space and non-breaking characters with a special glyph.

tab-mark
     Draw tab characters with a special glyph.

newline-mark
     Draw newline characters with a special glyph.

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 graphical displays, 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.

On graphical displays, the mode line is drawn as a 3D box.  If you don't like this effect, you can disable it by customizing the mode-line face and setting its box attribute to nil.  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
=====================

Most characters are printing characters: when they appear in a buffer, they are displayed literally on the screen.  Printing characters include ASCII numbers, letters, and punctuation characters, as well as many non-ASCII characters.

The ASCII character set contains non-printing control characters.  Two of these are displayed specially: the newline character (Unicode code point U+000A) is displayed by starting a new line, while the tab character (U+0009) is displayed as a space that extends to the next tab stop column (normally every 8 columns).  The number of spaces per tab is controlled by the buffer-local variable tab-width, which must have an integer value between 1 and 1000, inclusive.  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, whose codes are below U+0020 (octal 40, decimal 32), are displayed as a caret (^) followed by the non-control version of the character, with the escape-glyph face.  For instance, the control-A character, U+0001, is displayed as ^A.

The raw bytes with codes U+0080 (octal 200) through U+009F (octal 237) are displayed as octal escape sequences, with the escape-glyph face.  For instance, character code U+0098 (octal 230) is displayed as \230. If you change the buffer-local variable ctl-arrow to nil, the ASCII control characters are also displayed as octal escape sequences instead of caret escape sequences.

Some non-ASCII characters have the same appearance as an ASCII space or hyphen (minus) character.  Such characters can cause problems if they are entered into a buffer without your realization, e.g. by yanking; for instance, source code compilers typically do not treat non-ASCII spaces as whitespace characters.  To deal with this problem, Emacs displays such characters specially: it displays U+00A0 (no-break space) with the nobreak-space face, and it displays U+00AD (soft hyphen), U+2010 (hyphen), and U+2011 (non-breaking hyphen) with the escape-glyph face.  To disable this, change the variable nobreak-char-display to nil.  If you give this variable a non-nil and non-t value, Emacs instead displays such characters as a highlighted backslash followed by a space or hyphen.

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 graphical displays, some characters may have no glyphs in any of the fonts available to Emacs.  These glyphless characters are normally displayed as boxes containing the hexadecimal character code. Similarly, on text terminals, characters that cannot be displayed using the terminal encoding (see Terminal Coding) are normally displayed as question signs.  You can control the display method by customizing the variable glyphless-char-display-control. See Glyphless Character Display (The Emacs Lisp Reference Manual), for details.

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

On a text terminal, the cursor's appearance is controlled by the terminal, largely out of the control of Emacs.  Some terminals offer two different cursors: a ``visible'' static cursor, and a ``very visible'' blinking cursor.  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 uses the normal cursor.

On a graphical display, many more properties of the text cursor can be altered.  To customize its color, change the :background attribute of the face named cursor (see Face Customization).  (The other attributes of this face have no effect; the text shown under the cursor is drawn using the frame's background color.)  To change its shape, customize the buffer-local variable cursor-type; possible values are box (the default), hollow (a hollow box), bar (a vertical bar), (bar . N) (a vertical bar N pixels wide), hbar (a horizontal bar), (hbar . N) (a horizontal bar N pixels tall), or nil (no cursor at all).

To disable cursor blinking, change the variable blink-cursor-mode to nil (see Easy Customization), or add the line (blink-cursor-mode 0) to your init file. Alternatively, you can change how the cursor looks when it ``blinks off'' by customizing the list variable blink-cursor-alist. Each element in the list should have the form (ON-TYPE . OFF-TYPE); this means that if the cursor is displayed as ON-TYPE when it blinks on (where ON-TYPE is one of the cursor types described above), then it is displayed as OFF-TYPE when it blinks off.

Some characters, such as tab characters, are ``extra wide''.  When the cursor is positioned over such a character, it is normally drawn with the default character width.  You can make the cursor stretch to cover wide characters, by changing the variable x-stretch-cursor to a non-nil value.

The cursor normally appears in non-selected windows as a non-blinking hollow box.  (For a bar cursor, it instead appears as a thinner bar.)  To turn off cursors in non-selected windows, change the variable cursor-in-non-selected-windows to nil.

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.

Line Truncation
===============

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 terminals, this is indicated with $ signs in the leftmost and/or rightmost columns.

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, which is normally nil, is in effect.

If a split window becomes too narrow, Emacs may automatically enable line truncation.  See Split Window, for the variable truncate-partial-width-windows which controls this.

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 that control miscellaneous aspects of the appearance of the Emacs screen.  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 something to echo.  See Echo Area.

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 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.