@c This is part of the Emacs manual.
@c Copyright (C) 1985, 1986, 1987, 1993 Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Screen, User Input, Concept Index, Top
@chapter The Organization of the Screen
@cindex screen
@c

  On a text-only terminal, the Emacs display occupies the whole screen.
On the X Window System, Emacs creates its own X windows to use.  We use
the term @dfn{frame} to mean an entire text-only screen or an entire X
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 under X you can create additional frames if you wish.  @xref{Frames}.

  When you start Emacs, the entire frame except for the last line is
devoted to the text you are editing.  This area is called @dfn{window}.
The last line is a special @dfn{echo area} or @dfn{minibuffer window}
where prompts appear and where you can enter responses.  You can
subdivide the large text window horizontally or vertically into multiple
text windows, each of which can be used for a different file
(@pxref{Windows}).  In this manual, the word ``window'' always refers to
the subdivisions of a frame within Emacs.

  The window that the cursor is in is the @dfn{selected window}, in
which editing takes place.  Most Emacs commands implicitly apply to the
text in the selected window.  The other windows display text for
reference only, unless/until you select them.

  Each window's last line is a @dfn{mode line} which describes what is
going on in that window.  It is in inverse video if the terminal
supports that, and contains text that starts like @samp{-----Emacs:@:
@var{something}}.  Its purpose is to indicate what buffer is being
displayed above it in the window; what major and minor modes are in use;
and whether the buffer contains unsaved changes.

@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.
@end menu

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

  Within Emacs, the terminal's cursor shows the location at which
editing commands will take effect.  This location is called
@dfn{point}.  Other commands move point through the text, so that you
can edit at different places in it.

  While the cursor appears to point @var{at} a character, you should
think of point as @var{between} two characters; it points @var{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.

  Terminals have only one cursor, and when output is in progress it must
appear where the typing is being done.  This does not mean that point is
moving.  It is only that Emacs has no way to show you the location of point
except when the terminal is idle.

  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 where point is in case you display it again later.

  When there are multiple windows, each window has its own point
location.  The cursor shows the location of point in the selected
window.  This also is how you can tell which window is selected.  If the
same buffer appears in more than one window, each window has its own
position for point in that buffer.

  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'.

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

  The line at the bottom of the screen (below the mode line) is the
@dfn{echo area}.  It is used to display small amounts of text for several
purposes.

  @dfn{Echoing} means printing out the characters that you type.
Outside Emacs, the operating system normally echoes all your input.
Emacs handles echoing differently.

  Single-character commands do not echo in Emacs, and multi-character
commands echo only if you pause while typing them.  As soon as you pause
for more than a second in the middle of a command, Emacs echoes all the
characters of the command so far.  This is to @dfn{prompt} you for the
rest of the command.  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.  You can change this behavior by setting a variable
(@pxref{Display Vars}).

  If a command cannot be executed, it may print an @dfn{error message} in
the echo area.  Error messages are accompanied by a beep or by flashing the
screen.  Also, any input you have typed ahead is thrown away when an error
happens.

  Some commands print informative messages in the echo area.  These
messages look much like error messages, but they are not announced with
a beep and do not throw away input.  Sometimes the message tells you
what the command has done, when this is not obvious from looking at the
text being edited.  Sometimes the sole purpose of a command is to print
a message giving you specific information---for example, @kbd{C-x =}
prints 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.

  The echo area is also used to display the @dfn{minibuffer}, a window that
is used for reading arguments to commands, such as the name of a file to be
edited.  When the minibuffer is in use, the echo area begins with a prompt
string that usually ends with a colon; also, the cursor appears in that line
because it is 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
@c

  Each text window's last line is a @dfn{mode line} which describes what is
going on in that window.  When there is only one text window, the mode line
appears right above the echo area.  The mode line is in inverse video if
the terminal supports that, starts and ends with dashes, and contains text
like @samp{Emacs:@: @var{something}}.

  If a mode line has something else in place of @samp{Emacs:@: @var{something}},
then the window above it is in a special subsystem such as Dired.  The mode
line then indicates the status of the subsystem.

  Normally, the mode line looks like this:

@example
--@var{ch}-Emacs: @var{buf}      (@var{major} @var{minor})----@var{pos}------
@end example

@noindent
This gives information about the buffer being displayed in the window: the
buffer's name, what major and minor modes are in use, whether the buffer's
text has been changed, and how far down the buffer you are currently
looking.

  @var{ch} contains two stars @samp{**} if the text in the buffer has been
edited (the buffer is ``modified''), or @samp{--} if the buffer has not been
edited.  Exception: for a read-only buffer, it is @samp{%%}.

  @var{buf} is the name of the window's @dfn{buffer}.  In most cases
this is the same as the name of a file you are editing.  @xref{Buffers}.

  The buffer displayed in the selected window (the window that the
cursor is in) is also Emacs's selected buffer, the one that editing
takes place in.  When we speak of what some command does to ``the
buffer'', we are talking about the currently selected buffer.

  @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.@refill

  @var{major} is the name of the @dfn{major mode} in effect in the buffer.  At
any time, each buffer is in one and only one of the possible major modes.
The major modes available include Fundamental mode (the least specialized),
Text mode, Lisp mode, and C mode.  @xref{Major Modes}, for details
of how the modes differ and how to select one.@refill

  @var{minor} is a list of some of the @dfn{minor modes} that are turned on
at the moment in the window's chosen buffer.  @samp{Fill} means that Auto
Fill mode is on.  @samp{Abbrev} means that Word Abbrev mode is on.
@samp{Ovwrt} means that Overwrite mode is on.  @xref{Minor Modes}, for more
information.  @samp{Narrow} means that the buffer being displayed has
editing restricted to only a portion of its text.  This is not really a
minor mode, but is like one.  @xref{Narrowing}.  @samp{Def} means that a
keyboard macro is being defined.  @xref{Keyboard Macros}.

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

  In addition, if Emacs is currently 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 and not any one buffer, the square
brackets appear in every window's mode line or not in any of them.
@xref{Recursive Edit}.@refill

  @xref{Optional Display}, for features that add other handy information
to the mode line, such as the current line number of point, the current
time, and whether mail has arrived for you.
