Improve documentation of glyphless-character display

[gnu-emacs] / doc / emacs / display.texi

@c -*- coding: utf-8 -*-
@c This is part of the Emacs manual.
@c Copyright (C) 1985-1987, 1993-1995, 1997, 2000-2016 Free Software
@c Foundation, Inc.

@c See file emacs.texi for copying conditions.
@node Display
@chapter 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.

@menu
* Scrolling::              Commands to move text up and down in a window.
* Recentering::            A scroll command that centers the current line.
* Auto Scrolling::         Redisplay scrolls text automatically when needed.
* Horizontal Scrolling::   Moving text left and right in a window.
* Narrowing::              Restricting display and editing to a portion
                             of the buffer.
* View Mode::              Viewing read-only buffers.
* Follow Mode::            Follow mode lets two windows scroll as one.
* Faces::                  How to change the display style using faces.
* Colors::                 Specifying colors for faces.
* Standard Faces::         The main predefined faces.
* Text Scale::             Increasing or decreasing text size in a buffer.
* Font Lock::              Minor mode for syntactic highlighting using faces.
* Highlight Interactively:: Tell Emacs what text to highlight.
* Fringes::                Enabling or disabling window fringes.
* Displaying Boundaries::  Displaying top and bottom of the buffer.
* Useless Whitespace::     Showing possibly spurious trailing whitespace.
* Selective Display::      Hiding lines with lots of indentation.
* Optional Mode Line::     Optional mode line display features.
* Text Display::           How text characters are normally displayed.
* Cursor Display::         Features for displaying the cursor.
* Line Truncation::        Truncating lines to fit the screen width instead
                             of continuing them to multiple screen lines.
* Visual Line Mode::       Word wrap and screen line-based editing.
* Display Custom::         Information on variables for customizing display.
@end menu

@node Scrolling
@section Scrolling
@cindex scrolling

  If a window is too small to display all the text in its buffer, it
displays only a portion of it.  @dfn{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, @emph{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 @key{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 (@pxref{Auto
Scrolling}).  You can also scroll explicitly with these commands:

@table @kbd
@item C-v
@itemx @key{next}
@itemx @key{PageDown}
Scroll forward by nearly a full window (@code{scroll-up-command}).
@item M-v
@itemx @key{prior}
@itemx @key{PageUp}
Scroll backward (@code{scroll-down-command}).
@end table

@kindex C-v
@kindex M-v
@kindex next
@kindex prior
@kindex PageDown
@kindex PageUp
@findex scroll-up-command
@findex scroll-down-command
  @kbd{C-v} (@code{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
@key{next} (or @key{PageDown}) key is equivalent to @kbd{C-v}.

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

@vindex next-screen-context-lines
  The number of lines of overlap left by these scroll commands is
controlled by the variable @code{next-screen-context-lines}, whose
default value is 2.  You can supply the commands with a numeric prefix
argument, @var{n}, to scroll by @var{n} lines; Emacs attempts to leave
point unchanged, so that the text and point move up or down together.
@kbd{C-v} with a negative argument is like @kbd{M-v} and vice versa.

@vindex scroll-error-top-bottom
  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 @code{scroll-error-top-bottom} to @code{t}, the command moves
point to the farthest possible position.  If point is already there,
the command signals an error.

@vindex scroll-preserve-screen-position
@cindex @code{scroll-command} property
  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 @code{scroll-preserve-screen-position}.  If the value
is @code{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-@code{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 (@pxref{Mouse Commands}); in general, it affects any
command that has a non-@code{nil} @code{scroll-command} property.
@xref{Property Lists,,, elisp, The Emacs Lisp Reference Manual}.

@vindex fast-but-imprecise-scrolling
  Sometimes, particularly when you hold down keys such as @kbd{C-v}
and @kbd{M-v}, activating keyboard auto-repeat, Emacs fails to keep up
with the rapid rate of scrolling requested; the display doesn't update
and Emacs can become unresponsive to input for quite a long time.  You
can counter this sluggishness by setting the variable
@code{fast-but-imprecise-scrolling} to a non-@code{nil} value.  This
instructs the scrolling commands not to fontify (@pxref{Font Lock})
any unfontified text they scroll over, instead to assume it has the
default face.  This can cause Emacs to scroll to somewhat wrong buffer
positions when the faces in use are not all the same size, even with
single (i.e., without auto-repeat) scrolling operations.

@vindex scroll-up
@vindex scroll-down
@findex scroll-up-line
@findex scroll-down-line
  The commands @kbd{M-x scroll-up} and @kbd{M-x scroll-down} behave
similarly to @code{scroll-up-command} and @code{scroll-down-command},
except they do not obey @code{scroll-error-top-bottom}.  Prior to
Emacs 24, these were the default commands for scrolling up and down.
The commands @kbd{M-x scroll-up-line} and @kbd{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
(@pxref{Init Rebinding}).

@node Recentering
@section Recentering

@table @kbd
@item 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 (@code{recenter-top-bottom}).

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

@item C-M-l
Scroll heuristically to bring useful information onto the screen
(@code{reposition-window}).
@end table

@kindex C-l
@findex recenter-top-bottom
  The @kbd{C-l} (@code{recenter-top-bottom}) command @dfn{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 @kbd{C-l} twice in a row (@kbd{C-l C-l}) scrolls the window
so that point is on the topmost screen line.  Typing a third @kbd{C-l}
scrolls the window so that point is on the bottom-most screen line.
Each successive @kbd{C-l} cycles through these three positions.

@vindex recenter-positions
  You can change the cycling order by customizing the list variable
@code{recenter-positions}.  Each list element should be the symbol
@code{top}, @code{middle}, or @code{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,
@code{(middle top bottom)}, is the cycling order described above.
Furthermore, if you change the variable @code{scroll-margin} to a
non-zero value @var{n}, @kbd{C-l} always leaves at least @var{n}
screen lines between point and the top or bottom of the window
(@pxref{Auto Scrolling}).

  You can also give @kbd{C-l} a prefix argument.  A plain prefix
argument, @kbd{C-u C-l}, simply recenters point.  A positive argument
@var{n} puts point @var{n} lines down from the top of the window.  An
argument of zero puts point on the topmost line.  A negative argument
@var{-n} puts point @var{n} lines from the bottom of the window.  When
given an argument, @kbd{C-l} does not clear the screen or cycle
through different screen positions.

@vindex recenter-redisplay
  If the variable @code{recenter-redisplay} has a non-@code{nil}
value, each invocation of @kbd{C-l} also clears and redisplays the
screen; the special value @code{tty} (the default) says to do this on
text-terminal frames only.  Redisplaying is useful in case the screen
becomes garbled for any reason (@pxref{Screen Garbled}).

@findex recenter
  The more primitive command @kbd{M-x recenter} behaves like
@code{recenter-top-bottom}, but does not cycle among screen positions.

@kindex C-M-l
@findex reposition-window
  @kbd{C-M-l} (@code{reposition-window}) scrolls the current window
heuristically in a way designed to get useful information onto the
screen.  For example, in a Lisp file, this command tries to get the
entire current defun onto the screen if possible.

@node Auto Scrolling
@section Automatic Scrolling

@cindex automatic scrolling
  Emacs performs @dfn{automatic scrolling} when point moves out of the
visible portion of the text.  Normally, automatic scrolling centers
point vertically in the window, but there are several ways to alter
this behavior.

@vindex scroll-conservatively
  If you set @code{scroll-conservatively} to a small number @var{n},
then moving point just a little off the screen (no more than @var{n}
lines) causes Emacs to scroll just enough to bring point back on
screen; if doing so fails to make point visible, Emacs scrolls just
far enough to center point in the window.  If you set
@code{scroll-conservatively} to a large number (larger than 100),
automatic scrolling never centers point, no matter how far point
moves; Emacs always scrolls text just enough to bring point into view,
either at the top or bottom of the window depending on the scroll
direction.  By default, @code{scroll-conservatively} is@tie{}0, which
means to always center point in the window.

@vindex scroll-step
  Another way to control automatic scrolling is to customize the
variable @code{scroll-step}.  Its value determines the number of lines
by which to automatically scroll, when point moves off the screen.  If
scrolling by that number of lines fails to bring point back into view,
point is centered instead.  The default value is zero, which (by
default) causes point to always be centered after scrolling.

@cindex aggressive scrolling
@vindex scroll-up-aggressively
@vindex scroll-down-aggressively
  A third way to control automatic scrolling is to customize the
variables @code{scroll-up-aggressively} and
@code{scroll-down-aggressively}, which directly specify the vertical
position of point after scrolling.  The value of
@code{scroll-up-aggressively} should be either @code{nil} (the
default), or a floating point number @var{f} between 0 and 1.  The
latter means that when point goes below the bottom window edge (i.e.,
scrolling forward), Emacs scrolls the window so that point is @var{f}
parts of the window height from the bottom window edge.  Thus, larger
@var{f} means more aggressive scrolling: more new text is brought into
view.  The default value, @code{nil}, is equivalent to 0.5.

  Likewise, @code{scroll-down-aggressively} is used when point goes
above the bottom window edge (i.e., scrolling backward).  The value
specifies how far point should be from the top margin of the window
after scrolling.  Thus, as with @code{scroll-up-aggressively}, a
larger value is more aggressive.

  Note that the variables @code{scroll-conservatively},
@code{scroll-step}, and @code{scroll-up-aggressively} /
@code{scroll-down-aggressively} control automatic scrolling in
contradictory ways.  Therefore, you should pick no more than one of
these methods to customize automatic scrolling.  In case you customize
multiple variables, the order of priority is:
@code{scroll-conservatively}, then @code{scroll-step}, and finally
@code{scroll-up-aggressively} / @code{scroll-down-aggressively}.

@vindex scroll-margin
  The variable @code{scroll-margin} restricts how close point can come
to the top or bottom of a window (even if aggressive scrolling
specifies a fraction @var{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,
@code{scroll-margin} is 0.

@node Horizontal Scrolling
@section Horizontal Scrolling
@cindex horizontal scrolling

@vindex auto-hscroll-mode
  @dfn{Horizontal scrolling} means shifting all the lines sideways
within a window, so that some of the text near the left margin is not
displayed.  When the text in a window is scrolled horizontally, text
lines are truncated rather than continued (@pxref{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
@code{auto-hscroll-mode} to @code{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.)

@vindex hscroll-margin
  The variable @code{hscroll-margin} controls how close point can get
to the window's left and right 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.

@vindex hscroll-step
  The variable @code{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:

@table @kbd
@item C-x <
Scroll text in current window to the left (@code{scroll-left}).
@item C-x >
Scroll to the right (@code{scroll-right}).
@end table

@kindex C-x <
@kindex C-x >
@findex scroll-left
@findex scroll-right
  @kbd{C-x <} (@code{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 @var{n}, it scrolls by @var{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
@code{auto-hscroll-mode}, which, for text scrolled to the left, only
affects the behavior at the right edge of the window.

  @kbd{C-x >} (@code{scroll-right}) scrolls similarly to the right.
The window cannot be scrolled any farther to the right once it is
displayed normally, with each line starting at the window's left
margin; attempting to do so has no effect.  This means that you don't
have to calculate the argument precisely for @w{@kbd{C-x >}}; any
sufficiently large argument will restore the normal display.

  If you use those commands to scroll a window horizontally, that sets
a lower bound for automatic horizontal scrolling.  Automatic scrolling
will continue to scroll the window, but never farther to the right
than the amount you previously set by @code{scroll-left}.

@node Narrowing
@section Narrowing
@cindex widening
@cindex restriction
@cindex narrowing
@cindex accessible portion

  @dfn{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 @dfn{accessible portion}.  Canceling the
narrowing, which makes the entire buffer once again accessible, is
called @dfn{widening}.  The bounds of narrowing in effect in a buffer
are called the buffer's @dfn{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.

@table @kbd
@item C-x n n
Narrow down to between point and mark (@code{narrow-to-region}).
@item C-x n w
Widen to make the entire buffer accessible again (@code{widen}).
@item C-x n p
Narrow down to the current page (@code{narrow-to-page}).
@item C-x n d
Narrow down to the current defun (@code{narrow-to-defun}).
@end table

  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 @samp{Narrow} appears in
the mode line whenever narrowing is in effect.

@kindex C-x n n
@findex narrow-to-region
  The primary narrowing command is @kbd{C-x n n} (@code{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.

@kindex C-x n p
@findex narrow-to-page
@kindex C-x n d
@findex narrow-to-defun
  Alternatively, use @kbd{C-x n p} (@code{narrow-to-page}) to narrow
down to the current page.  @xref{Pages}, for the definition of a page.
@kbd{C-x n d} (@code{narrow-to-defun}) narrows down to the defun
containing point (@pxref{Defuns}).

@kindex C-x n w
@findex widen
  The way to cancel narrowing is to widen with @kbd{C-x n w}
(@code{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 @kbd{C-x =} command.  @xref{Position Info}.

  Because narrowing can easily confuse users who do not understand it,
@code{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.  @xref{Disabling}.

@node View Mode
@section View Mode
@cindex View mode
@cindex mode, View

@kindex s @r{(View mode)}
@kindex SPC @r{(View mode)}
@kindex DEL @r{(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 @key{SPC} to scroll forward one
windowful, @kbd{S-@key{SPC}} or @key{DEL} to scroll backward, and @kbd{s} to
start an incremental search.

@kindex q @r{(View mode)}
@kindex e @r{(View mode)}
@findex View-quit
@findex View-exit
  Typing @kbd{q} (@code{View-quit}) disables View mode, and switches
back to the buffer and position before View mode was enabled.  Typing
@kbd{e} (@code{View-exit}) disables View mode, keeping the current
buffer and position.

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

@node Follow Mode
@section Follow Mode
@cindex Follow mode
@cindex mode, Follow
@findex follow-mode
@cindex windows, synchronizing
@cindex synchronizing windows

  @dfn{Follow mode} is a minor mode that makes two windows, both
showing the same buffer, scroll as a single tall virtual window.
To use Follow mode, go to a frame with just one window, split it into
two side-by-side windows using @kbd{C-x 3}, and then type @kbd{M-x
follow-mode}.  From then on, you can edit the buffer in either of the
two windows, or scroll either one; the other window follows it.

  In Follow mode, if you move point outside the portion visible in one
window and into the portion visible in the other window, that selects
the other window---again, treating the two as if they were parts of
one large window.

  To turn off Follow mode, type @kbd{M-x follow-mode} a second time.

@node Faces
@section Text Faces
@cindex faces

  Emacs can display text in several different styles, called
@dfn{faces}.  Each face can specify various @dfn{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.  @xref{Font Lock}, for
more information about how these faces are assigned.

@findex list-faces-display
  To see what faces are currently defined, and what they look like,
type @kbd{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 (@pxref{Regexps}).

@vindex frame-background-mode
  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 @code{frame-background-mode}
a non-@code{nil} value.  A value of @code{dark} makes Emacs treat all
frames as if they have a dark background, whereas a value of
@code{light} makes it treat all frames as if they have a light
background.

@cindex background color
@cindex default face
  You can customize a face to alter its attributes, and save those
customizations for future Emacs sessions.  @xref{Face Customization},
for details.

  The @code{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.  @xref{Colors}.

@cindex cursor face
  Another special face is the @code{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 @code{cursor} face.

  You can also use X resources to specify attributes of any particular
face.  @xref{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.

@node Colors
@section Colors for Faces
@cindex color name
@cindex RGB triplet

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

@findex list-colors-display
@vindex list-colors-sort
  A color name is a pre-defined name, such as @samp{dark orange} or
@samp{medium sea green}.  To view a list of color names, type @kbd{M-x
list-colors-display}.  To control the order in which colors are shown,
customize @code{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
@file{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 @samp{#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 @kbd{M-x list-colors-display} command also shows the equivalent
RGB triplet for each named color.  For instance, @samp{medium sea
green} is equivalent to @samp{#3CB371}.

@cindex face colors, setting
@findex set-face-foreground
@findex set-face-background
  You can change the foreground and background colors of a face with
@kbd{M-x set-face-foreground} and @kbd{M-x set-face-background}.
These commands prompt in the minibuffer for a face name and a color,
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; @xref{Frame
Parameters}.

@node Standard Faces
@section Standard Faces
@cindex 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.

@table @code
@item 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.
@item bold
This face uses a bold variant of the default font.
@item italic
This face uses an italic variant of the default font.
@item bold-italic
This face uses a bold italic variant of the default font.
@item underline
This face underlines text.
@item 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.
@cindex variable-pitch face
@item variable-pitch
This face forces use of a variable-width font.
@cindex shadow face
@item 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.
@end table

  Here's an incomplete list of faces used to highlight parts of the
text temporarily for specific purposes.  (Many other modes define
their own faces for this purpose.)

@table @code
@item highlight
This face is used for text highlighting in various contexts, such as
when the mouse cursor is moved over a hyperlink.
@item isearch
This face is used to highlight the current Isearch match
(@pxref{Incremental Search}).
@item query-replace
This face is used to highlight the current Query Replace match
(@pxref{Replace}).
@item lazy-highlight
This face is used to highlight lazy matches for Isearch and Query
Replace (matches other than the current one).
@item region
This face is used for displaying an active region (@pxref{Mark}).
When Emacs is built with GTK support, its colors are taken from the
current GTK theme.
@item secondary-selection
This face is used for displaying a secondary X selection (@pxref{Secondary
Selection}).
@item trailing-whitespace
The face for highlighting excess spaces and tabs at the end of a line
when @code{show-trailing-whitespace} is non-@code{nil} (@pxref{Useless
Whitespace}).
@item escape-glyph
The face for displaying control characters and escape sequences
(@pxref{Text Display}).
@item nobreak-space
The face for displaying no-break space characters (@pxref{Text
Display}).
@end table

  The following faces control the appearance of parts of the Emacs
frame:

@table @code
@item mode-line
@cindex mode-line face
@cindex faces for mode lines
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.
@item mode-line-inactive
@cindex mode-line-inactive face
Like @code{mode-line}, but used for mode lines of the windows other
than the selected one (if @code{mode-line-in-non-selected-windows} is
non-@code{nil}).  This face inherits from @code{mode-line}, so changes
in that face affect mode lines in all windows.
@item mode-line-highlight
@cindex mode-line-highlight face
Like @code{highlight}, but used for mouse-sensitive portions of text
on mode lines.  Such portions of text typically pop up tooltips
(@pxref{Tooltips}) when the mouse pointer hovers above them.
@item mode-line-buffer-id
@cindex mode-line-buffer-id face
This face is used for buffer identification parts in the mode line.
@item header-line
@cindex header-line face
Similar to @code{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.
@item vertical-border
@cindex vertical-border face
This face is used for the vertical divider between windows on text
terminals.
@item minibuffer-prompt
@cindex @code{minibuffer-prompt} face
@vindex minibuffer-prompt-properties
This face is used for the prompt strings displayed in the minibuffer.
By default, Emacs automatically adds this face to the value of
@code{minibuffer-prompt-properties}, which is a list of text
properties (@pxref{Text Properties,,, elisp, the Emacs Lisp Reference
Manual}) used to display the prompt text.  (This variable takes effect
when you enter the minibuffer.)
@item fringe
@cindex @code{fringe} face
The face for the fringes to the left and right of windows on graphic
displays.  (The fringes are the narrow portions of the Emacs frame
between the text area and the window's right and left borders.)
@xref{Fringes}.
@item cursor
The @code{:background} attribute of this face specifies the color of
the text cursor.  @xref{Cursor Display}.
@item 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.  @xref{Tooltips}.
@item mouse
This face determines the color of the mouse pointer.
@end table

  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.)

@table @code
@item scroll-bar
This face determines the visual appearance of the scroll bar.
@xref{Scroll Bars}.
@item tool-bar
This face determines the color of tool bar icons.  @xref{Tool Bars}.
@item menu
@cindex menu bar appearance
@cindex @code{menu} face, no effect if customized
@cindex customization of @code{menu} face
This face determines the colors and font of Emacs's menus.  @xref{Menu
Bars}.
@item tty-menu-enabled-face
@cindex faces for text-mode menus
@cindex TTY menu faces
This face is used to display enabled menu items on text-mode
terminals.
@item tty-menu-disabled-face
This face is used to display disabled menu items on text-mode
terminals.
@item tty-menu-selected-face
This face is used to display on text-mode terminals the menu item that
would be selected if you click a mouse or press @key{RET}.
@end table

@node Text Scale
@section Text Scale

@cindex adjust buffer face height
@findex text-scale-adjust
@kindex C-x C-+
@kindex C-x C--
@kindex C-x C-=
@kindex C-x C-0
  To increase the height of the default face in the current buffer,
type @kbd{C-x C-+} or @kbd{C-x C-=}.  To decrease it, type @kbd{C-x
C--}.  To restore the default (global) face height, type @kbd{C-x
C-0}.  These keys are all bound to the same command,
@code{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
@kbd{C-x}.  For instance, @kbd{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
@code{text-scale-mode-step}.  A numeric argument of 0
to the @code{text-scale-adjust} command restores the default height,
the same as typing @kbd{C-x C-0}.

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

@cindex set buffer face height
@findex text-scale-set
  The command @code{text-scale-set} scales the height of the default
face in the current buffer to an absolute level specified by its
prefix argument.

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

@node Font Lock
@section Font Lock mode
@cindex Font Lock mode
@cindex mode, Font Lock
@cindex syntax highlighting and coloring

  Font Lock mode is a minor mode, always local to a particular buffer,
which assigns faces to (or @dfn{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.

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

@findex global-font-lock-mode
@vindex global-font-lock-mode
  Type @kbd{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 @code{global-font-lock-mode} (@pxref{Easy
Customization}), or add the following line to your init file:

@example
(global-font-lock-mode 0)
@end example

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

@example
(add-hook 'c-mode-hook 'font-lock-mode)
@end example

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

@vindex font-lock-maximum-decoration
  You can customize the variable @code{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 @code{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

@example
'((c-mode . 1) (c++-mode . 1)))
@end example

@cindex incorrect fontification
@cindex parenthesis in column zero and fontification
@cindex brace in column zero and fontification
  Comment and string fontification (or ``syntactic'' fontification)
relies on analysis of the syntactic structure of the buffer text.  For
the sake of speed, some modes, including 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.  @xref{Left Margin Paren}, for details.

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

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

@findex font-lock-remove-keywords
@noindent
To remove keywords from the font-lock highlighting patterns, use the
function @code{font-lock-remove-keywords}.  @xref{Search-based
Fontification,,, elisp, The Emacs Lisp Reference Manual}.

@cindex just-in-time (JIT) font-lock
@cindex background syntax highlighting
  Fontifying large buffers can take a long time.  To avoid large
delays when a file is visited, Emacs 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 @dfn{Just-In-Time} (or @dfn{JIT})
Lock.  You can control how JIT Lock behaves, including telling it to
perform fontification while idle, by customizing variables in the
customization group @samp{jit-lock}.  @xref{Specific Customization}.

@node Highlight Interactively
@section Interactive Highlighting
@cindex highlighting by matching
@cindex interactive highlighting
@cindex Highlight Changes mode

@findex highlight-changes-mode
Highlight Changes mode is a minor mode that @dfn{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
@kbd{M-x highlight-changes-mode}.

@cindex Hi Lock mode
@findex hi-lock-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 @kbd{M-x hi-lock-mode}.  To enable Hi Lock
mode for all buffers, use @kbd{M-x global-hi-lock-mode} or place
@code{(global-hi-lock-mode 1)} in your @file{.emacs} file.

  Hi Lock mode works like Font Lock mode (@pxref{Font Lock}), except
that you specify explicitly the regular expressions to highlight.  You
control them with the commands described below.  (The key bindings
below that begin with @kbd{C-x w} are deprecated in favor of the
global @kbd{M-s h} bindings, and will be removed in some future Emacs
version.)

@table @kbd
@item M-s h r @var{regexp} @key{RET} @var{face} @key{RET}
@itemx C-x w h @var{regexp} @key{RET} @var{face} @key{RET}
@kindex M-s h r
@kindex C-x w h
@findex highlight-regexp
Highlight text that matches @var{regexp} using face @var{face}
(@code{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)
@kbd{M-s h r whim @key{RET} @key{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 @kbd{M-n} and @kbd{M-p} to cycle through them.

@vindex hi-lock-auto-select-face
Setting the option @code{hi-lock-auto-select-face} to a non-@code{nil}
value causes this command (and other Hi Lock commands that read faces)
to automatically choose the next face from the default list without
prompting.

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

@item M-s h u @var{regexp} @key{RET}
@itemx C-x w r @var{regexp} @key{RET}
@kindex M-s h u
@kindex C-x w r
@findex unhighlight-regexp
Unhighlight @var{regexp} (@code{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 @kbd{M-n} to show the next older expression and
@kbd{M-p} 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 @kbd{@key{RET}} to exit
the minibuffer and unhighlight it.

@item M-s h l @var{regexp} @key{RET} @var{face} @key{RET}
@itemx C-x w l @var{regexp} @key{RET} @var{face} @key{RET}
@kindex M-s h l
@kindex C-x w l
@findex highlight-lines-matching-regexp
@cindex lines, highlighting
@cindex highlighting lines of text
Highlight entire lines containing a match for @var{regexp}, using face
@var{face} (@code{highlight-lines-matching-regexp}).

@item M-s h p @var{phrase} @key{RET} @var{face} @key{RET}
@itemx C-x w p @var{phrase} @key{RET} @var{face} @key{RET}
@kindex M-s h p
@kindex C-x w p
@findex highlight-phrase
@cindex phrase, highlighting
@cindex highlighting phrase
Highlight matches of @var{phrase}, using face @var{face}
(@code{highlight-phrase}).  @var{phrase} can be any regexp,
but spaces will be replaced by matches to whitespace and
initial lower-case letters will become case insensitive.

@item M-s h .
@itemx C-x w .
@kindex M-s h .
@kindex C-x w .
@findex highlight-symbol-at-point
@cindex symbol, highlighting
@cindex highlighting symbol at point
Highlight the symbol found near point, using the next available face
(@code{highlight-symbol-at-point}).

@item M-s h w
@itemx C-x w b
@kindex M-s h w
@kindex C-x w b
@findex hi-lock-write-interactive-patterns
Insert all the current highlighting regexp/face pairs into the buffer
at point, with comment delimiters to prevent them from changing your
program.  (This key binding runs the
@code{hi-lock-write-interactive-patterns} command.)

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

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

@vindex hi-lock-file-patterns-policy
The variable @code{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 @code{nil} (never highlight),
@code{ask} (query the user), or a function.  If it is a function,
@code{hi-lock-find-patterns} calls it with the patterns as argument; if
the function returns non-@code{nil}, the patterns are used.  The default
is @code{ask}.  Note that patterns are always highlighted if you call
@code{hi-lock-find-patterns} directly, regardless of the value of this
variable.

@vindex hi-lock-exclude-modes
Also, @code{hi-lock-find-patterns} does nothing if the current major
mode's symbol is a member of the list @code{hi-lock-exclude-modes}.
@end table

@node Fringes
@section Window Fringes
@cindex fringes

@findex set-fringe-style
@findex fringe-mode
@vindex fringe-mode @r{(variable)}
  On graphical displays, each Emacs window normally has narrow
@dfn{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 @kbd{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 @kbd{M-x set-fringe-style}.
You can make your changes to the fringes permanent by customizing the
variable @code{fringe-mode}.

  The most common use of the fringes is to indicate a continuation
line (@pxref{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 (@pxref{Bidirectional
Editing}), the meanings of the curving arrows in the fringes are
swapped.

  The fringes indicate line truncation (@pxref{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 (@pxref{Displaying Boundaries}), and where a program you
are debugging is executing (@pxref{Debuggers}).

@vindex overflow-newline-into-fringe
  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
@code{overflow-newline-into-fringe} to @code{nil}; this causes Emacs
to continue or truncate lines that are exactly as wide as the window.

@node Displaying Boundaries
@section Displaying Boundaries

@vindex indicate-buffer-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 @code{indicate-buffer-boundaries} controls
how the buffer boundaries and window scrolling is indicated in the
fringes.  If the value is @code{left} or @code{right}, both angle and
arrow bitmaps are displayed in the left or right fringe, respectively.

  If value is an alist (@pxref{Association Lists,,, elisp, the Emacs
Lisp Reference Manual}), each element @code{(@var{indicator} .
@var{position})} specifies the position of one of the indicators.  The
@var{indicator} must be one of @code{top}, @code{bottom}, @code{up},
@code{down}, or @code{t} which specifies the default position for the
indicators not present in the alist.  The @var{position} is one of
@code{left}, @code{right}, or @code{nil} which specifies not to show
this indicator.

  For example, @code{((top . left) (t . right))} places the top angle
bitmap in left fringe, the bottom angle bitmap in right fringe, and
both arrow bitmaps in right fringe.  To show just the angle bitmaps in
the left fringe, but no arrow bitmaps, use @code{((top .  left)
(bottom . left))}.

@node Useless Whitespace
@section Useless Whitespace

@cindex trailing whitespace
@cindex whitespace, trailing
@vindex show-trailing-whitespace
  It is easy to leave unnecessary spaces at the end of a line, or
empty lines at the end of a buffer, without realizing it.  In most
cases, this @dfn{trailing whitespace} has no effect, but sometimes it
can be a nuisance.

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

  This feature does not apply when point is at the end of the line
containing the whitespace.  Strictly speaking, that is trailing
whitespace nonetheless, but displaying it specially in that case
looks ugly while you are typing in new text.  In this special case,
the location of point is enough to show you that the spaces are
present.

@findex delete-trailing-whitespace
@vindex delete-trailing-lines
  Type @kbd{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 @code{delete-trailing-lines} to
@code{nil}.  If the region is active, the command instead deletes
extra spaces at the end of each line in the region.

@vindex indicate-empty-lines
@cindex unused lines
@cindex fringes, and unused line indication
  On graphical displays, Emacs can indicate unused lines at the end of
the window with a small image in the left fringe (@pxref{Fringes}).
The image appears for 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 @code{indicate-empty-lines} to a non-@code{nil} value.  You
can enable or disable this feature for all new buffers by setting the
default value of this variable, e.g., @code{(setq-default
indicate-empty-lines t)}.

@cindex Whitespace mode
@cindex mode, Whitespace
@findex whitespace-mode
@vindex whitespace-style
@findex whitespace-toggle-options
  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 @kbd{M-x
whitespace-mode}.  The kinds of whitespace visualized are determined
by the list variable @code{whitespace-style}.  Individual elements in
that list can be toggled on or off in the current buffer by typing
@w{@kbd{M-x whitespace-toggle-options}}.  Here is a partial list
of possible elements (see the variable's documentation for the full
list):

@table @code
@item 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 @code{space-mark}, @code{tab-mark},
and @code{newline-mark}.

@item trailing
Highlight trailing whitespace.

@item tabs
Highlight tab characters.

@item spaces
Highlight space and non-breaking space characters.

@item lines
@vindex whitespace-line-column
Highlight lines longer than 80 columns.  To change the column limit,
customize the variable @code{whitespace-line-column}.

@item newline
Highlight newlines.

@item empty
Highlight empty lines.

@item big-indent
@vindex whitespace-big-indent-regexp
Highlight too-deep indentation.  By default any sequence of at least 4
consecutive TAB characters or 32 consecutive SPC characters is
highlighted.  To change that, customize the regular expression
@code{whitespace-big-indent-regexp}.

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

@item tab-mark
Draw tab characters with a special glyph.

@item newline-mark
Draw newline characters with a special glyph.
@end table

@findex global-whitespace-toggle-options
@findex global-whitespace-mode
Global Whitespace mode is a global minor mode that lets you visualize
whitespace in all buffers.  To toggle individual features, use
@kbd{M-x global-whitespace-toggle-options}.

@node Selective Display
@section Selective Display
@cindex selective display
@findex set-selective-display
@kindex C-x $

  Emacs has the ability to hide lines indented more than a 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 @kbd{C-x $}
(@code{set-selective-display}) with a numeric argument @var{n}.  Then
lines with at least @var{n} columns of indentation disappear from the
screen.  The only indication of their presence is that three dots
(@samp{@dots{}}) appear at the end of each visible line that is
followed by one or more hidden ones.

  The commands @kbd{C-n} and @kbd{C-p} move across the hidden lines as
if they were not there.

  The hidden lines are still present in the buffer, and most editing
commands see them as usual, so you may find point in the middle of the
hidden text.  When this happens, the cursor appears at the end of the
previous line, after the three dots.  If point is at the end of the
visible line, before the newline that ends it, the cursor appears before
the three dots.

  To make all lines visible again, type @kbd{C-x $} with no argument.

@vindex selective-display-ellipses
  If you set the variable @code{selective-display-ellipses} to
@code{nil}, the three dots do not appear at the end of a line that
precedes hidden lines.  Then there is no visible indication of the
hidden lines.  This variable becomes local automatically when set.

  See also @ref{Outline Mode} for another way to hide part of
the text in a buffer.

@node Optional Mode Line
@section Optional Mode Line Features

@cindex buffer size display
@cindex display of buffer size
@findex size-indication-mode
  The buffer percentage @var{pos} indicates the percentage of the
buffer above the top of the window.  You can additionally display the
size of the buffer by typing @kbd{M-x size-indication-mode} to turn on
Size Indication mode.  The size will be displayed immediately
following the buffer percentage like this:

@example
@var{pos} of @var{size}
@end example

@noindent
Here @var{size} is the human readable representation of the number of
characters in the buffer, which means that @samp{k} for 10^3, @samp{M}
for 10^6, @samp{G} for 10^9, etc., are used to abbreviate.

@cindex line number display
@cindex display of line number
@findex line-number-mode
  The current line number of point appears in the mode line when Line
Number mode is enabled.  Use the command @kbd{M-x line-number-mode} to
turn this mode on and off; normally it is on.  The line number appears
after the buffer percentage @var{pos}, with the letter @samp{L} to
indicate what it is.

@cindex Column Number mode
@cindex mode, Column Number
@findex column-number-mode
  Similarly, you can display the current column number by turning on
Column number mode with @kbd{M-x column-number-mode}.  The column
number is indicated by the letter @samp{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 @samp{L} and
@samp{C}.  For example: @samp{(561,2)}.  @xref{Minor Modes}, for more
information about minor modes and about how to use these commands.

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

@vindex line-number-display-limit
  If the buffer is very large (larger than the value of
@code{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
@code{line-number-display-limit} to @code{nil}.

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

@findex display-time
@cindex time (on mode line)
  Emacs can optionally display the time and system load in all mode
lines.  To enable this feature, type @kbd{M-x display-time} or customize
the option @code{display-time-mode}.  The information added to the mode
line looks like this:

@example
@var{hh}:@var{mm}pm @var{l.ll}
@end example

@noindent
@vindex display-time-24hr-format
Here @var{hh} and @var{mm} are the hour and minute, followed always by
@samp{am} or @samp{pm}.  @var{l.ll} is the average number, 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 @code{display-time-24hr-format} to @code{t}.

@cindex mail (on mode line)
@vindex display-time-use-mail-icon
@vindex display-time-mail-face
@vindex display-time-mail-file
@vindex display-time-mail-directory
  The word @samp{Mail} appears after the load level if there is mail
for you that you have not read yet.  On graphical displays, you can
use an icon instead of @samp{Mail} by customizing
@code{display-time-use-mail-icon}; this may save some space on the
mode line.  You can customize @code{display-time-mail-face} to make
the mail indicator prominent.  Use @code{display-time-mail-file} to
specify the mail file to check, or set
@code{display-time-mail-directory} to specify the directory to check
for incoming mail (any nonempty regular file in the directory is
considered to be newly arrived mail).

@cindex battery status (on mode line)
@findex display-battery-mode
@vindex display-battery-mode
@vindex battery-mode-line-format
  When running Emacs on a laptop computer, you can display the battery
charge on the mode-line, by using the command
@code{display-battery-mode} or customizing the variable
@code{display-battery-mode}.  The variable
@code{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.

@cindex mode line, 3D appearance
@cindex attributes of mode line, changing
@cindex non-integral number of lines in a window
  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
@code{mode-line} face and setting its @code{box} attribute to
@code{nil}.  @xref{Face Customization}.

@cindex non-selected windows, mode line appearance
  By default, the mode line of nonselected windows is displayed in a
different face, called @code{mode-line-inactive}.  Only the selected
window is displayed in the @code{mode-line} face.  This helps show
which window is selected.  When the minibuffer is selected, since
it has no mode line, the window from which you activated the minibuffer
has its mode line displayed using @code{mode-line}; as a result,
ordinary entry to the minibuffer does not change any mode lines.

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

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

@node Text Display
@section How Text Is Displayed
@cindex characters (in text)
@cindex printing character

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

@vindex tab-width
@cindex control characters on display
  The @acronym{ASCII} character set contains non-printing @dfn{control
characters}.  Two of these are displayed specially: the newline
character (Unicode code point @code{U+000A}) is displayed by starting
a new line, while the tab character (@code{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 @code{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
@key{TAB} as a command.

  Other @acronym{ASCII} control characters, whose codes are below
@code{U+0020} (octal 40, decimal 32), are displayed as a caret
(@samp{^}) followed by the non-control version of the character, with
the @code{escape-glyph} face.  For instance, the @samp{control-A}
character, @code{U+0001}, is displayed as @samp{^A}.

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

@vindex nobreak-char-display
@cindex non-breaking space
@cindex non-breaking hyphen
@cindex soft hyphen
@cindex escape-glyph face
@cindex nobreak-space face
  Some non-@acronym{ASCII} characters have the same appearance as an
@acronym{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-@acronym{ASCII} spaces as whitespace
characters.  To deal with this problem, Emacs displays such characters
specially: it displays @code{U+00A0} (no-break space) with the
@code{nobreak-space} face, and it displays @code{U+00AD} (soft
hyphen), @code{U+2010} (hyphen), and @code{U+2011} (non-breaking
hyphen) with the @code{escape-glyph} face.  To disable this, change
the variable @code{nobreak-char-display} to @code{nil}.  If you give
this variable a non-@code{nil} and non-@code{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.  @xref{Display Tables,, Display Tables,
elisp, The Emacs Lisp Reference Manual}.

@cindex glyphless characters
@cindex characters with no font glyphs
@cindex glyphless-char face
  On graphical displays, some characters may have no glyphs in any of
the fonts available to Emacs.  These @dfn{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 (@pxref{Terminal Coding}) are normally
displayed as question signs.  You can control the display method by
customizing the variable @code{glyphless-char-display-control}.  You
can also customize the @code{glyphless-char} face to make these
characters more prominent on display.  @xref{Glyphless Chars,,
Glyphless Character Display, elisp, The Emacs Lisp Reference Manual},
for details.

@cindex curly quotes
@cindex curved quotes
@cindex escape-glyph face
  If the curved quotes @samp{‘}, @samp{’}, @samp{“}, and @samp{”} are
known to look just like @acronym{ASCII} characters, they are shown
with the @code{escape-glyph} face.  Curved quotes that cannot be
displayed are shown as their @acronym{ASCII} approximations @samp{`},
@samp{'}, and @samp{"} with the @code{escape-glyph} face.

@node Cursor Display
@section Displaying the Cursor
@cindex text cursor

@vindex visible-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 @code{visible-cursor} is @code{nil} when Emacs starts or
resumes, it uses the normal cursor.

@cindex cursor face
@vindex cursor-type
  On a graphical display, many more properties of the text cursor can
be altered.  To customize its color, change the @code{:background}
attribute of the face named @code{cursor} (@pxref{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
@code{cursor-type}; possible values are @code{box} (the default),
@code{hollow} (a hollow box), @code{bar} (a vertical bar), @code{(bar
. @var{n})} (a vertical bar @var{n} pixels wide), @code{hbar} (a
horizontal bar), @code{(hbar . @var{n})} (a horizontal bar @var{n}
pixels tall), or @code{nil} (no cursor at all).

@findex blink-cursor-mode
@cindex cursor, blinking
@cindex blinking cursor
@vindex blink-cursor-mode
@vindex blink-cursor-blinks
@vindex blink-cursor-alist
  By default, the cursor stops blinking after 10 blinks, if Emacs does
not get any input during that time; any input event restarts the
count.  You can customize the variable @code{blink-cursor-blinks} to
control that: its value says how many times to blink without input
before stopping.  Setting that variable to a zero or negative value
will make the cursor blink forever.  To disable cursor blinking
altogether, change the variable @code{blink-cursor-mode} to @code{nil}
(@pxref{Easy Customization}), or add the line

@lisp
  (blink-cursor-mode 0)
@end lisp

@noindent
to your init file.  Alternatively, you can change how the cursor
looks when it blinks off by customizing the list variable
@code{blink-cursor-alist}.  Each element in the list should have the
form @code{(@var{on-type} . @var{off-type})}; this means that if the
cursor is displayed as @var{on-type} when it blinks on (where
@var{on-type} is one of the cursor types described above), then it is
displayed as @var{off-type} when it blinks off.

@vindex x-stretch-cursor
@cindex wide block cursor
  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
@code{x-stretch-cursor} to a non-@code{nil} value.

@cindex cursor in non-selected windows
@vindex cursor-in-non-selected-windows
  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 @code{cursor-in-non-selected-windows} to @code{nil}.

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

@node Line Truncation
@section Line Truncation

@cindex truncation
@cindex line truncation, and fringes
  As an alternative to continuation (@pxref{Continuation Lines}),
Emacs can display long lines by @dfn{truncation}.  This means that all
the characters that do not fit in the width of the screen or window do
not appear at all.  On graphical displays, a small straight arrow in
the fringe indicates truncation at either end of the line.  On text
terminals, this is indicated with @samp{$} signs in the leftmost
and/or rightmost columns.

@vindex truncate-lines
@findex toggle-truncate-lines
  Horizontal scrolling automatically causes line truncation
(@pxref{Horizontal Scrolling}).  You can explicitly enable line
truncation for a particular buffer with the command @kbd{M-x
toggle-truncate-lines}.  This works by locally changing the variable
@code{truncate-lines}.  If that variable is non-@code{nil}, long lines
are truncated; if it is @code{nil}, they are continued onto multiple
screen lines.  Setting the variable @code{truncate-lines} in any way
makes it local to the current buffer; until that time, the default
value, which is normally @code{nil}, is in effect.

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

@node Visual Line Mode
@section Visual Line Mode

@cindex word wrap
  Another alternative to ordinary line continuation is to use
@dfn{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.

@cindex mode, Visual Line
@cindex Visual Line mode
@findex visual-line-mode
@findex global-visual-line-mode
  Word wrap is enabled by Visual Line mode, an optional minor mode.
To turn on Visual Line mode in the current buffer, type @kbd{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 @samp{Line Wrapping in this Buffer} submenu, followed by
the @samp{Word Wrap (Visual Line Mode)} menu item.  While Visual Line
mode is enabled, the mode-line shows the string @samp{wrap} in the
mode display.  The command @kbd{M-x global-visual-line-mode} toggles
Visual Line mode in all buffers.

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

  To move by logical lines, use the commands @kbd{M-x
next-logical-line} and @kbd{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.  @xref{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 @code{visual-line-fringe-indicators}.

@node Display Custom
@section Customization of Display

  This section describes variables that control miscellaneous aspects
of the appearance of the Emacs screen.  Beginning users can skip it.

@vindex visible-bell
  If the variable @code{visible-bell} is non-@code{nil}, Emacs attempts
to make the whole screen blink when it would normally make an audible bell
sound.  This variable has no effect if your terminal does not have a way
to make the screen blink.

@vindex echo-keystrokes
  The variable @code{echo-keystrokes} controls the echoing of multi-character
keys; its value is the number of seconds of pause required to cause echoing
to start, or zero, meaning don't echo at all.  The value takes effect when
there is something to echo.  @xref{Echo Area}.

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

@vindex make-pointer-invisible
  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.  @xref{Inserting Text}.)  Moving
the mouse pointer makes it visible again.  To disable this feature,
set the variable @code{make-pointer-invisible} to @code{nil}.

@vindex underline-minimum-offset
@vindex x-underline-at-descent-line
  On graphical displays, the variable @code{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 @code{x-underline-at-descent-line} determines how
to draw underlined text.  The default is @code{nil}, which means to
draw it at the baseline level of the font; if you change it to
@code{nil}, Emacs draws the underline at the same height as the font's
descent line.

@vindex overline-margin
  The variable @code{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.

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