* progmodes/prolog.el (prolog-mode): Use define-derived-mode.

[emacs.git] / doc / emacs / screen.texi

@c This is part of the Emacs manual.
@c Copyright (C) 1985, 1986, 1987, 1993, 1994, 1995, 1997, 2001, 2002,
@c   2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010 Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Screen, User Input, Acknowledgments, Top
@chapter The Organization of the Screen
@cindex screen
@cindex parts of the screen

  On a text-only terminal, the Emacs display occupies the entire
terminal screen.  On a graphical display, such as on GNU/Linux using
the X Window System, Emacs creates its own windows to use.  We use the
term @dfn{frame} to mean the entire terminal screen or graphical
window used by Emacs.  Emacs uses both kinds of frames, in the same
way, to display your editing.  Emacs normally starts out with just one
frame, but you can create additional frames if you wish
(@pxref{Frames}).

  The frame consists of several distinct regions.  At the top of the
frame is a @dfn{menu bar}, which allows you to access commands via a
series of menus.  On a graphical display, directly below the menu bar
is a @dfn{tool bar}, a row of icons that perform editing commands if
you click on them.  At the very bottom of the frame is a special
@dfn{echo area}, where short informative messages are displayed and
where you enter information when Emacs asks for it.

  The main area of the frame, below the tool bar (if one exists) and
above the echo area, is called @dfn{the window}.  This is where Emacs
displays the @dfn{buffer}: the text that you are editing.  On a
graphical display, the window possesses a @dfn{scroll bar} on one
side, which you can use to display different parts of the buffer in
the window.  The last line of the window is a @dfn{mode line}.  This
displays various information about what is going on in the buffer,
such as whether there are unsaved changes, the editing modes that are
in use, the current line number, and so forth.

  When you start Emacs, there is normally only one window in the
frame.  However, you can subdivide this window horizontally or
vertically to create multiple windows, each of which can independently
display a buffer (@pxref{Windows}).  In this manual, the word
``window'' refers to the initial large window if not subdivided, or
any one of the multiple windows you have subdivided it into.

  At any time, one window is the @dfn{selected window}.  On graphical
displays, the selected window normally shows a more prominent cursor
(usually solid and blinking) while other windows show a weaker cursor
(such as a hollow box).  Text terminals have just one cursor, so it
always appears in the selected window.  The buffer displayed in the
selected window is called the @dfn{current buffer}, and it is where
editing happens.  Most Emacs commands implicitly apply to the current
buffer; the text displayed in unselected windows is mostly visible for
reference.  If you use multiple frames on a graphical display,
selecting a particular frame selects a window in that frame.

@menu
* Point::               The place in the text where editing commands operate.
* Echo Area::           Short messages appear at the bottom of the screen.
* Mode Line::           Interpreting the mode line.
* Menu Bar::            How to use the menu bar.
@end menu

@node Point
@section Point
@cindex point
@cindex cursor

  The active cursor shows the location at which editing commands will
take effect, which is called @dfn{point}@footnote{The term ``point''
comes from the character @samp{.}, which was the command in TECO (the
language in which the original Emacs was written) for accessing the
value now called ``point.''}.  Many Emacs commands move point to
different places in the buffer; for example, you can place point by
clicking mouse button 1 (normally the left button) at the desired
location.

  While the cursor appears to be @emph{on} a character, you should
think of point as @emph{between} two characters; it points @emph{before}
the character that appears under the cursor.  For example, if your text
looks like @samp{frob} with the cursor over the @samp{b}, then point is
between the @samp{o} and the @samp{b}.  If you insert the character
@samp{!} at that position, the result is @samp{fro!b}, with point
between the @samp{!} and the @samp{b}.  Thus, the cursor remains over
the @samp{b}, as before.

  Sometimes people speak of ``the cursor'' when they mean ``point,'' or
speak of commands that move point as ``cursor motion'' commands.

  If you are editing several files in Emacs, each in its own buffer,
each buffer has its own point location.  A buffer that is not
currently displayed remembers its point location in case you display
it again later.  When Emacs displays multiple windows, each window has
its own point location.  If the same buffer appears in more than one
window, each window has its own point position in that buffer.

  On a graphical display, Emacs shows a cursor in each window; the
selected window's cursor is solid and blinking, and the other cursors
are hollow.  On a text-only terminal, there is just one cursor, in the
selected window; even though the unselected windows have their own
point positions, they do not display a cursor.  @xref{Cursor Display},
for customizable variables that control cursor display.

@node Echo Area
@section The Echo Area
@cindex echo area

  The line at the very bottom of the frame is the @dfn{echo area}.  It
is used to display small amounts of text for various purposes.

  @dfn{Echoing} means displaying the characters that you type.
Single-character commands, including most simple editing operations,
are not echoed.  Multi-character commands are echoed if you pause
while typing them: if you pause for more than a second in the middle
of a command, Emacs echoes all the characters of the command so far,
to prompt you for the rest of the command.  The echoed characters are
displayed in the echo area.  Once echoing has started, the rest of the
command echoes immediately as you type it.  This behavior is designed
to give confident users fast response, while giving hesitant users
maximum feedback.  @xref{Display Custom}.

@cindex error message in the echo area
  If a command cannot do its job, it may display an @dfn{error
message}.  Error messages are also displayed in the echo area.  They
may be accompanied by beeping or by flashing the screen.

  Some commands display informative messages in the echo area.  Unlike
error messages, these messages are not announced with a beep or flash.
Sometimes the message tells you what the command has done, when this
is not obvious from looking at the text being edited.  Other times,
the sole purpose of a command is to show you a message giving you
specific information.  For example, @kbd{C-x =} (hold down @key{CTRL}
and type @kbd{x}, then let go of @key{CTRL} and type @kbd{=}) displays
a message describing the character position of point in the text and
its current column in the window.  Commands that take a long time
often display messages ending in @samp{...} while they are working,
and add @samp{done} at the end when they are finished.  They may also
indicate progress with percentages.

@cindex @samp{*Messages*} buffer
@cindex saved echo area messages
@cindex messages saved from echo area
@vindex message-log-max
  Informative echo-area messages are saved in a special buffer named
@samp{*Messages*}.  (We have not explained buffers yet; see
@ref{Buffers}, for more information about them.)  If you miss a
message that appeared briefly on the screen, you can switch to the
@samp{*Messages*} buffer to see it again.  The @samp{*Messages*}
buffer is limited to a certain number of lines, specified by the
variable @code{message-log-max}.  (We have not explained variables
either; see @ref{Variables}, for more information about them.)  Beyond
this limit, one line is deleted from the beginning whenever a new
message line is added at the end.

@cindex minibuffer
  The echo area is also used to display the @dfn{minibuffer}, a
special window where you can input arguments to commands, such as the
name of a file to be edited.  When the minibuffer is in use, the text
displayed in the echo area begins with a @dfn{prompt string} (usually
ending with a colon); also, the active cursor appears within the
minibuffer, which is temporarily considered the selected window.  You
can always get out of the minibuffer by typing @kbd{C-g}.
@xref{Minibuffer}.

@node Mode Line
@section The Mode Line
@cindex mode line
@cindex top level

  At the bottom of each window is a @dfn{mode line}, which describes
what is going on in the current buffer.  When there is only one
window, the mode line appears right above the echo area; it is the
next-to-last line in the frame.  On a graphical display, the mode line
is drawn with a 3D box appearance, and the mode line of the selected
window has a brighter color than that of unselected windows to make it
stand out.  On a text-only terminal, the mode line is usually drawn in
inverse video.

  The text displayed in the mode line has the following format:

@example
-@var{cs}:@var{ch}-@var{fr}  @var{buf}      @var{pos} @var{line}   (@var{major} @var{minor})------
@end example

@noindent
The @var{cs} string and the colon character after it describe the
character set and newline convention used for the current buffer.
Normally, Emacs handles these settings intelligently, but it is
sometimes useful to have this information.

  @var{cs} describes the character set of the buffer (@pxref{Coding
Systems}).  If it is a dash (@samp{-}), that indicates the default
state of affairs: no special character set handling, except for the
end-of-line translations described in the next paragraph.  @samp{=}
means no conversion whatsoever.  Letters represent various nontrivial
@dfn{coding systems}---for example, @samp{1} represents ISO Latin-1.
On a text-only terminal, @var{cs} is preceded by two additional
characters that describe the coding system for keyboard input and the
coding system for terminal output.  Furthermore, if you are using an
input method, @var{cs} is preceded by a string that identifies the
input method, which takes the form @samp{@var{i}>}, @samp{@var{i}+},
or @samp{@var{i}@@} (@pxref{Input Methods}).

@cindex end-of-line conversion, mode-line indication
  The character after @var{cs} is usually a colon.  However, under
some circumstances a different string is displayed, which indicates a
nontrivial end-of-line convention.  Usually, lines of text are
separated by @dfn{newline characters}, but two other conventions are
sometimes used.  The MS-DOS convention is to use a ``carriage-return''
character followed by a ``linefeed'' character; when editing such
files, the colon changes to either a backslash (@samp{\}) or
@samp{(DOS)}, depending on the operating system.  The Macintosh
end-of-line convention is to use a ``carriage-return'' character
instead of a newline; when editing such files, the colon indicator
changes to either a forward slash (@samp{/}) or @samp{(Mac)}.  On some
systems, Emacs displays @samp{(Unix)} instead of the colon for files
that use newline as the line separator.

  The next element on the mode line is the string indicated by
@var{ch}.  This shows two dashes (@samp{--}) if the buffer displayed
in the window has the same contents as the corresponding file on the
disk; i.e., if the buffer is ``unmodified''.  If the buffer is
modified, it shows two stars (@samp{**}).  For a read-only buffer, it
shows @samp{%*} if the buffer is modified, and @samp{%%} otherwise.

  The character after @var{ch} is normally a dash (@samp{-}).
However, if the default-directory for the current buffer is on a
remote machine, @samp{@@} is displayed instead (@pxref{File Names}).

  @var{fr} gives the selected frame name (@pxref{Frames}).  It appears
only on text-only terminals.  The initial frame's name is @samp{F1}.

  @var{buf} is the name of the buffer displayed in the window.
Usually, this is the same as the name of a file you are editing.
@xref{Buffers}.

  @var{pos} tells you whether there is additional text above the top of
the window, or below the bottom.  If your buffer is small and it is all
visible in the window, @var{pos} is @samp{All}.  Otherwise, it is
@samp{Top} if you are looking at the beginning of the buffer, @samp{Bot}
if you are looking at the end of the buffer, or @samp{@var{nn}%}, where
@var{nn} is the percentage of the buffer above the top of the window.
With Size Indication mode, you can display the size of the buffer as
well.  @xref{Optional Mode Line}.

  @var{line} is the character @samp{L} followed by the line number at
point.  (You can display the current column number too, by turning on
Column Number mode.  @xref{Optional Mode Line}.)

  @var{major} is the name of the @dfn{major mode} used in the buffer.
A major mode is a principal editing mode for the buffer, such as Text
mode, Lisp mode, C mode, and so forth.  @xref{Major Modes}.

  Some major modes display additional information after the major mode
name.  For example, Rmail buffers display the current message number and
the total number of messages.  Compilation buffers and Shell buffers
display the status of the subprocess.

  @var{minor} is a list of some of the @dfn{minor modes} turned on in
the buffer.  Minor modes are optional editing modes that provide
additional features on top of the major mode.  @xref{Minor Modes}.

  Some features are listed together with the minor modes whenever they
are turned on, even through they are not really minor modes.
@samp{Narrow} means that the buffer being displayed has editing
restricted to only a portion of its text (@pxref{Narrowing}).
@samp{Def} means that a keyboard macro is currently being defined
(@pxref{Keyboard Macros}).

  In addition, if Emacs is inside a recursive editing level, square
brackets (@samp{[@dots{}]}) appear around the parentheses that
surround the modes.  If Emacs is in one recursive editing level within
another, double square brackets appear, and so on.  Since recursive
editing levels affect Emacs globally, not just one buffer, the square
brackets appear in every window's mode line or not in any of them.
@xref{Recursive Edit}.@refill

  You can change the appearance of the mode line as well as the format
of its contents.  @xref{Optional Mode Line}.  In addition, the mode
line is mouse-sensitive; clicking on different parts of the mode line
performs various commands.  @xref{Mode Line Mouse}.

@node Menu Bar
@section The Menu Bar
@cindex menu bar

  Each Emacs frame normally has a @dfn{menu bar} at the top which you
can use to perform common operations.  There's no need to list them
here, as you can more easily see them yourself.

@kindex M-`
@kindex F10
@findex tmm-menubar
@findex menu-bar-open
  On a graphical display, you can use the mouse to choose a command
from the menu bar.  A right-arrow at the end of a menu item means it
leads to a subsidiary menu, or @dfn{submenu}.  A @samp{...} at the end
of a menu item means that the command invoked will prompt you for
further input before it actually does anything.

  Some of the commands in the menu bar have ordinary key bindings as
well; if so, a key binding is shown in parentheses after the item
itself.  To view the full command name and documentation for a menu
item, type @kbd{C-h k}, and then select the menu bar with the mouse in
the usual way (@pxref{Key Help}).

  Instead of using the mouse, you can also invoke the first menu bar
item by pressing @key{F10} (to run the command @code{menu-bar-open}).
You can then navigate the menus with the arrow keys.  To activate a
selected menu item, press @key{RET}; to cancel menu navigation, press
@key{ESC}.

  On text-only terminals with no mouse, you can use the menu bar by
typing @kbd{M-`} or @key{F10} (these run the command
@code{tmm-menubar}).  This lets you select a menu item with the
keyboard.  A provisional choice appears in the echo area.  You can use
the up and down arrow keys to move through the menu to different
items, and then you can type @key{RET} to select the item.

  Each menu item also has an assigned letter or digit which designates
that item; it is usually the initial of some word in the item's name.
This letter or digit is separated from the item name by @samp{=>}.  You
can type the item's letter or digit to select the item.

@ignore
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@end ignore