resume Emacs, use the appropriate command in the parent shell---most
likely @code{fg}.
+@cindex controlling terminal
+ Suspending works only on a terminal device from which the Emacs
+session was started. We call that device the @dfn{controlling
+terminal} of the session.
+
Some operating systems do not support suspension of jobs; on these
systems, ``suspension'' actually creates a new shell temporarily as a
subprocess of Emacs. Then you would exit the shell to return to Emacs.
If and when the superior process resumes Emacs, @code{suspend-emacs}
returns @code{nil} to its caller in Lisp.
+This function works only on the controlling terminal of the Emacs
+session; to relinquish control of other tty devices, use
+@code{suspend-tty} (see below). If the Emacs session uses more than
+one terminal device, you will need to delete the frames on all the
+other devices before suspending Emacs, otherwise this function signals
+an error.
+
If @var{string} is non-@code{nil}, its characters are sent to be read
as terminal input by Emacs's superior shell. The characters in
@var{string} are not echoed by the superior shell; only the results
after a suspension.
@end defvar
+@defun suspend-tty &optional tty
+If @var{tty} specifies a terminal device used by Emacs, this function
+relinquishes the device and restores it to its prior state. Frames
+that used the device continue to exist, but are not updated and Emacs
+doesn't read input from them. If @var{tty} is a frame, it means that
+frame's terminal; if it is @code{nil}, the function uses the selected
+frame's terminal. If @var{tty} is already suspended, the function
+does nothing.
+
+This function runs the hook @code{suspend-tty-functions} (each
+function gets one argument, the terminal that corresponds to
+@var{tty}).
+@end defun
+
+@defun resume-tty &optional tty
+Resume the previously suspended terminal device @var{tty}. If
+@var{tty} is a frame, it means resume that frame's terminal;
+@code{nil} means the selected frame.
+
+This function reopens the terminal device, re-initializes it, and
+redraws its with that terminal's selected frame. It then runs the
+hook @code{resume-tty-functions}, passing each function the terminal
+which corresponds to @var{tty}.
+
+If the same device is already used by another Emacs terminal, this
+function signals an error.
+@end defun
+
+@defun controlling-tty-p &optional terminal
+This function returns non-@code{nil} if @var{terminal} is the
+controlling terminal device of the Emacs session.
+@end defun
+
+@deffn Command suspend-frame
+This command @dfn{suspends} a frame. For GUI frames, it calls
+@code{iconify-frame} (@pxref{Visibility of Frames}); for text-only
+frames, it calls either @code{suspend-emacs} or @code{suspend-tty},
+depending on whether the frame is displayed on the controlling
+terminal device or not.
+@end deffn
+
@node System Environment
@section Operating System Environment
@cindex operating system environment
AT&T System V.
@item windows-nt
-Microsoft windows NT. The same executable supports Windows 9X, but the
-value of @code{system-type} is @code{windows-nt} in either case.
+Microsoft Windows NT and later. The same executable supports Windows
+9X, but the value of @code{system-type} is @code{windows-nt} in either
+case.
@end table
specifies the variable, and the other ``duplicates'' are ignored.
@end defvar
+@defvar initial-environment
+This variable holds the list of environment variables Emacs inherited
+from its parent process. It is computed during startup, see
+@ref{Startup Summary}.
+@end defvar
+
@defvar path-separator
This variable holds a string which says which character separates
directories in a search path (as found in an environment variable). Its