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+@c -*-texinfo-*-
+@c This is part of the GNU Emacs Lisp Reference Manual.
+@c Copyright (C) 1990, 1991, 1992, 1993 Free Software Foundation, Inc. 
+@c See the file elisp.texi for copying conditions.
+@setfilename ../info/internals
+@node GNU Emacs Internals, Standard Errors, Tips, Top
+@comment  node-name,  next,  previous,  up
+@appendix GNU Emacs Internals
+
+This chapter describes how the runnable Emacs executable is dumped with
+the preloaded Lisp libraries in it, how storage is allocated, and some
+internal aspects of GNU Emacs that may be of interest to C programmers.
+
+@menu
+* Building Emacs::      How to preload Lisp libraries into Emacs.
+* Pure Storage::        A kludge to make preloaded Lisp functions sharable.
+* Garbage Collection::  Reclaiming space for Lisp objects no longer used.
+* Writing Emacs Primitives::   Writing C code for Emacs.
+* Object Internals::    Data formats of buffers, windows, processes.
+@end menu
+
+@node Building Emacs, Pure Storage, GNU Emacs Internals, GNU Emacs Internals
+@appendixsec Building Emacs
+@cindex building Emacs
+@pindex temacs
+
+  This section explains the steps involved in building the Emacs
+executable.  You don't have to know this material to build and install
+Emacs, since the makefiles do all these things automatically.  This
+information is pertinent to Emacs maintenance.
+
+   Compilation of the C source files in the @file{src} directory
+produces an executable file called @file{temacs}, also called a
+@dfn{bare impure Emacs}.  It contains the Emacs Lisp interpreter and I/O
+routines, but not the editing commands.
+
+@cindex @file{loadup.el}
+  The command @w{@samp{temacs -l loadup}} uses @file{temacs} to create
+the real runnable Emacs executable.  These arguments direct
+@file{temacs} to evaluate the Lisp files specified in the file
+@file{loadup.el}.  These files set up the normal Emacs editing
+environment, resulting in an Emacs which is still impure but no longer
+bare.
+
+  It takes a substantial time to load the standard Lisp files.  Luckily,
+you don't have to do this each time you run Emacs; @file{temacs} can
+dump out an executable program called @file{emacs} which has these files
+preloaded.  @file{emacs} starts more quickly because it does not need to
+load the files.  This is the Emacs executable that is normally
+installed.
+
+  To create @file{emacs}, use the command @samp{temacs -batch -l loadup
+dump}.  The purpose of @samp{-batch} here is to prevent @file{temacs}
+from trying to initialize any of its data on the terminal; this ensures
+that the tables of terminal information are empty in the dumped Emacs.
+The argument @samp{dump} tells @file{loadup.el} to dump a new executable
+named @file{emacs}.
+
+  Some operating systems don't support dumping.  On those systems, you
+must start Emacs with the @samp{temacs -l loadup} command each time you
+use it.  This takes a long time, but since you need to start Emacs once
+a day at most---or once a week if you never log out---the extra time is
+not too severe a problem.
+
+@cindex @file{site-load.el}
+  You can specify additional files to preload by writing a library named
+@file{site-load.el} which loads them.  You may need to increase the
+value of @code{PURESIZE}, in @file{src/puresize.h}, to make room for the
+additional files.  (Try adding increments of 20000 until it is big
+enough.)  However, the advantage of preloading additional files
+decreases as machines get faster.  On modern machines, it is usually not
+advisable.
+
+@cindex @file{site-init.el}
+  You can specify other things to be done in Lisp just before dumping by
+putting them in a library named @file{site-init.el}.  However, if these
+things might alter the behavior that users expect from an ordinary
+unmodified Emacs, it is better to do them in @file{default.el}, so that
+users can override them if they wish.  @xref{Start-up Summary}.
+
+  Before @file{emacs} is dumped, the documentation strings for primitive
+and preloaded functions (and variables) need to be found in the file
+where they are stored.  This is done by calling
+@code{Snarf-documentation} (@pxref{Accessing Documentation}).  These
+strings were moved out of @file{emacs} to make it smaller.
+@xref{Documentation Basics}.
+
+@defun dump-emacs to-file from-file
+@cindex unexec
+  This function dumps the current state of Emacs into an executable file
+@var{to-file}.  It takes symbols from @var{from-file} (this is normally
+the executable file @file{temacs}).
+
+If you use this function in an Emacs that was already dumped, you must
+set @code{command-line-processed} to @code{nil} first for good results.
+@xref{Command Line Arguments}.
+@end defun
+
+@deffn Command emacs-version
+  This function returns a string describing the version of Emacs that is
+running.  It is useful to include this string in bug reports.
+
+@example
+@group
+(emacs-version)
+  @result{} "GNU Emacs 19.22.1 of Fri Feb 27 1994 \
+on slug (berkeley-unix)"
+@end group
+@end example
+
+Called interactively, the function prints the same information in the
+echo area.
+@end deffn
+
+@defvar emacs-build-time
+  The value of this variable is the time at which Emacs was built at the
+local site.
+
+@example
+@group
+emacs-build-time
+     @result{} "Fri Feb 27 14:55:57 1994"
+@end group
+@end example
+@end defvar
+
+@defvar emacs-version
+The value of this variable is the version of Emacs being run.  It is a
+string such as @code{"19.22.1"}.
+@end defvar
+
+@node Pure Storage, Garbage Collection, Building Emacs, GNU Emacs Internals
+@appendixsec Pure Storage
+@cindex pure storage
+
+  There are two types of storage in GNU Emacs Lisp for user-created Lisp
+objects: @dfn{normal storage} and @dfn{pure storage}.  Normal storage is
+where all the new data which is created during an Emacs session is kept;
+see the following section for information on normal storage.  Pure
+storage is used for certain data in the preloaded standard Lisp files:
+data that should never change during actual use of Emacs.
+
+  Pure storage is allocated only while @file{temacs} is loading the
+standard preloaded Lisp libraries.  In the file @file{emacs}, it is
+marked as read-only (on operating systems which permit this), so that
+the memory space can be shared by all the Emacs jobs running on the
+machine at once.  Pure storage is not expandable; a fixed amount is
+allocated when Emacs is compiled, and if that is not sufficient for the
+preloaded libraries, @file{temacs} crashes.  If that happens, you will
+have to increase the compilation parameter @code{PURESIZE} in the file
+@file{src/puresize.h}.  This normally won't happen unless you try to
+preload additional libraries or add features to the standard ones.
+
+@defun purecopy object
+  This function makes a copy of @var{object} in pure storage and returns
+it.  It copies strings by simply making a new string with the same
+characters in pure storage.  It recursively copies the contents of
+vectors and cons cells.  It does not make copies of symbols, or any
+other objects, but just returns them unchanged.  It signals an error if
+asked to copy markers.
+
+This function is used only while Emacs is being built and dumped; it is
+called only in the file @file{emacs/lisp/loaddefs.el}.
+@end defun
+
+@defvar pure-bytes-used
+  The value of this variable is the number of bytes of pure storage
+allocated so far.  Typically, in a dumped Emacs, this number is very
+close to the total amount of pure storage available---if it were not,
+we would preallocate less.
+@end defvar
+
+@defvar purify-flag
+  This variable determines whether @code{defun} should make a copy of the
+function definition in pure storage.  If it is non-@code{nil}, then the
+function definition is copied into pure storage.
+
+  This flag is @code{t} while loading all of the basic functions for
+building Emacs initially (allowing those functions to be sharable and
+non-collectible).  It is set to @code{nil} when Emacs is saved out
+as @file{emacs}.  The flag is set and reset in the C sources.
+
+ You should not change this flag in a running Emacs.
+@end defvar
+
+@node Garbage Collection, Writing Emacs Primitives, Pure Storage, GNU Emacs Internals
+@appendixsec Garbage Collection
+@cindex garbage collector
+
+@cindex memory allocation
+  When a program creates a list or the user defines a new function (such
+as by loading a library), then that data is placed in normal storage.
+If normal storage runs low, then Emacs asks the operating system to
+allocate more memory in blocks of 1k bytes.  Each block is used for one
+type of Lisp object, so symbols, cons cells, markers, etc.@: are
+segregated in distinct blocks in memory.  (Vectors, buffers and certain
+other editing types, which are fairly large, are allocated in individual
+blocks, one per object, while strings are packed into blocks of 8k
+bytes.)
+
+  It is quite common to use some storage for a while, then release it
+by, for example, killing a buffer or deleting the last pointer to an
+object.  Emacs provides a @dfn{garbage collector} to reclaim this
+abandoned storage.  (This name is traditional, but ``garbage recycler''
+might be a more intuitive metaphor for this facility.)
+
+  The garbage collector operates by scanning all the objects that have
+been allocated and marking those that are still accessible to Lisp
+programs.  To begin with, all the symbols, their values and associated
+function definitions, and any data presently on the stack, are
+accessible.  Any objects which can be reached indirectly through other
+accessible objects are also accessible.
+
+  When this is finished, all inaccessible objects are garbage.  No
+matter what the Lisp program or the user does, it is impossible to refer
+to them, since there is no longer a way to reach them.  Their
+space might as well be reused, since no one will notice.  That is what
+the garbage collector arranges to do.
+
+@cindex free list
+  Unused cons cells are chained together onto a @dfn{free list} for
+future allocation; likewise for symbols and markers.  The accessible
+strings are compacted so they are contiguous in memory; then the rest of
+the space formerly occupied by strings is made available to the string
+creation functions.  Vectors, buffers, windows and other large objects
+are individually allocated and freed using @code{malloc}.
+
+@cindex CL note---allocate more storage
+@quotation
+@b{Common Lisp note:} unlike other Lisps, GNU Emacs Lisp does not
+call the garbage collector when the free list is empty.  Instead, it
+simply requests the operating system to allocate more storage, and
+processing continues until @code{gc-cons-threshold} bytes have been
+used.
+
+This means that you can make sure that the garbage collector will not
+run during a certain portion of a Lisp program by calling the garbage
+collector explicitly just before it (provided that portion of the
+program does not use so much space as to force a second garbage
+collection).
+@end quotation
+
+@deffn Command garbage-collect
+  This command runs a garbage collection, and returns information on
+the amount of space in use.  (Garbage collection can also occur
+spontaneously if you use more than @code{gc-cons-threshold} bytes of
+Lisp data since the previous garbage collection.)
+
+  @code{garbage-collect} returns a list containing the following
+information:
+
+@smallexample
+@group
+((@var{used-conses} . @var{free-conses})
+ (@var{used-syms} . @var{free-syms})
+ (@var{used-markers} . @var{free-markers})
+ @var{used-string-chars} 
+ @var{used-vector-slots}
+ (@var{used-floats} . @var{free-floats}))
+
+(garbage-collect)
+     @result{} ((3435 . 2332) (1688 . 0)
+           (57 . 417) 24510 3839 (4 . 1))
+@end group
+@end smallexample
+
+Here is a table explaining each element:
+
+@table @var
+@item used-conses
+The number of cons cells in use.
+
+@item free-conses
+The number of cons cells for which space has been obtained from the
+operating system, but that are not currently being used.
+
+@item used-syms
+The number of symbols in use.
+
+@item free-syms
+The number of symbols for which space has been obtained from the
+operating system, but that are not currently being used.
+
+@item used-markers
+The number of markers in use.
+
+@item free-markers
+The number of markers for which space has been obtained from the
+operating system, but that are not currently being used.
+
+@item used-string-chars
+The total size of all strings, in characters.
+
+@item used-vector-slots
+The total number of elements of existing vectors.
+
+@item used-floats
+@c Emacs 19 feature
+The number of floats in use.
+
+@item free-floats
+@c Emacs 19 feature
+The number of floats for which space has been obtained from the
+operating system, but that are not currently being used.
+@end table
+@end deffn
+
+@defopt gc-cons-threshold
+  The value of this variable is the number of bytes of storage that must
+be allocated for Lisp objects after one garbage collection in order to
+request another garbage collection.  A cons cell counts as eight bytes,
+a string as one byte per character plus a few bytes of overhead, and so
+on.  (Space allocated to the contents of buffers does not count.)  Note
+that the new garbage collection does not happen immediately when the
+threshold is exhausted, but only the next time the Lisp evaluator is
+called.
+
+  The initial threshold value is 100,000.  If you specify a larger
+value, garbage collection will happen less often.  This reduces the
+amount of time spent garbage collecting, but increases total memory use.
+You may want to do this when running a program which creates lots of
+Lisp data.
+
+  You can make collections more frequent by specifying a smaller value,
+down to 10,000.  A value less than 10,000 will remain in effect only
+until the subsequent garbage collection, at which time
+@code{garbage-collect} will set the threshold back to 10,000.
+@end defopt
+
+@c Emacs 19 feature
+@defun memory-limit
+This function returns the address of the last byte Emacs has allocated,
+divided by 1024.  We divide the value by 1024 to make sure it fits in a
+Lisp integer.
+
+You can use this to get a general idea of how your actions affect the
+memory usage.
+@end defun
+
+@node Writing Emacs Primitives, Object Internals, Garbage Collection, GNU Emacs Internals
+@appendixsec Writing Emacs Primitives
+@cindex primitive function internals
+
+  Lisp primitives are Lisp functions implemented in C.  The details of
+interfacing the C function so that Lisp can call it are handled by a few
+C macros.  The only way to really understand how to write new C code is
+to read the source, but we can explain some things here.
+
+  An example of a special form is the definition of @code{or}, from
+@file{eval.c}.  (An ordinary function would have the same general
+appearance.)
+
+@cindex garbage collection protection
+@smallexample
+@group
+DEFUN ("or", For, Sor, 0, UNEVALLED, 0,
+  "Eval args until one of them yields non-NIL, then return that value.\n\
+The remaining args are not evalled at all.\n\
+@end group
+@group
+If all args return NIL, return NIL.")
+  (args)
+     Lisp_Object args;
+@{
+  register Lisp_Object val;
+  Lisp_Object args_left;
+  struct gcpro gcpro1;
+@end group
+
+@group
+  if (NULL(args))
+    return Qnil;
+
+  args_left = args;
+  GCPRO1 (args_left);
+@end group
+
+@group
+  do
+    @{
+      val = Feval (Fcar (args_left));
+      if (!NULL (val))
+        break;
+      args_left = Fcdr (args_left);
+    @}
+  while (!NULL(args_left));
+@end group
+
+@group
+  UNGCPRO;
+  return val;
+@}
+@end group
+@end smallexample
+
+  Let's start with a precise explanation of the arguments to the
+@code{DEFUN} macro.  Here are the general names for them:
+
+@example
+DEFUN (@var{lname}, @var{fname}, @var{sname}, @var{min}, @var{max}, @var{interactive}, @var{doc})
+@end example
+
+@table @var
+@item lname
+This is the name of the Lisp symbol to define with this
+function; in the example above, it is @code{or}.
+
+@item fname
+This is the C function name for this function.  This is
+the name that is used in C code for calling the function.  The name is,
+by convention, @samp{F} prepended to the Lisp name, with all dashes
+(@samp{-}) in the Lisp name changed to underscores.  Thus, to call this
+function from C code, call @code{For}.  Remember that the arguments must
+be of type @code{Lisp_Object}; various macros and functions for creating
+values of type @code{Lisp_Object} are declared in the file
+@file{lisp.h}.
+
+@item sname
+This is a C variable name to use for a structure that holds the data for
+the subr object that represents the function in Lisp.  This structure
+conveys the Lisp symbol name to the initialization routine that will
+create the symbol and store the subr object as its definition.  By
+convention, this name is always @var{fname} with @samp{F} replaced with
+@samp{S}.
+
+@item min
+This is the minimum number of arguments that the function requires.  For
+@code{or}, no arguments are required.
+
+@item max
+This is the maximum number of arguments that the function accepts.
+Alternatively, it can be @code{UNEVALLED}, indicating a special form
+that receives unevaluated arguments.  A function with the equivalent of
+an @code{&rest} argument would have @code{MANY} in this position.  Both
+@code{UNEVALLED} and @code{MANY} are macros.  This argument must be one
+of these macros or a number at least as large as @var{min}.  It may not
+be greater than six.
+
+@item interactive
+This is an interactive specification, a string such as might be used as
+the argument of @code{interactive} in a Lisp function.  In the case of
+@code{or}, it is 0 (a null pointer), indicating that @code{or} cannot be
+called interactively.  A value of @code{""} indicates an interactive
+function taking no arguments.
+
+@item doc
+This is the documentation string.  It is written just like a
+documentation string for a function defined in Lisp, except you must
+write @samp{\n\} at the end of each line.  In particular, the first line
+should be a single sentence.
+@end table
+
+  After the call to the @code{DEFUN} macro, you must write the list
+of argument names that every C function must have, followed by
+ordinary C declarations for them.  Normally, all the arguments must
+be declared as @code{Lisp_Object}.  If the function has no upper limit
+on the number of arguments in Lisp, then in C it receives two arguments:
+the number of Lisp arguments, and the address of a block containing their
+values.  These have types @code{int} and @w{@code{Lisp_Object *}}.
+
+  Within the function @code{For} itself, note the use of the macros
+@code{GCPRO1} and @code{UNGCPRO}.  @code{GCPRO1} is used to ``protect''
+a variable from garbage collection---to inform the garbage collector that
+it must look in that variable and regard its contents as an accessible
+object.  This is necessary whenever you call @code{Feval} or anything
+that can directly or indirectly call @code{Feval}.  At such a time, any
+Lisp object that you intend to refer to again must be protected somehow.
+@code{UNGCPRO} cancels the protection of the variables that are
+protected in the current function.  It is necessary to do this explicitly.
+
+  For most data types, it suffices to know that one pointer to the
+object is protected; as long as the object is not recycled, all pointers
+to it remain valid.  This is not so for strings, because the garbage
+collector can move them.  When a string is moved, any pointers to it
+that the garbage collector does not know about will not be properly
+relocated.  Therefore, all pointers to strings must be protected across
+any point where garbage collection may be possible.
+
+  The macro @code{GCPRO1} protects just one local variable.  If you
+want to protect two, use @code{GCPRO2} instead; repeating @code{GCPRO1}
+will not work.  There are also @code{GCPRO3} and @code{GCPRO4}.
+
+  In addition to using these macros, you must declare the local
+variables such as @code{gcpro1} which they implicitly use.  If you
+protect two variables, with @code{GCPRO2}, you must declare
+@code{gcpro1} and @code{gcpro2}, as it uses them both.  Alas, we can't
+explain all the tricky details here.
+
+  Defining the C function is not enough; you must also create the
+Lisp symbol for the primitive and store a suitable subr object
+in its function cell.  This is done by adding code to an initialization
+routine.  The code looks like this:
+
+@example
+defsubr (&@var{subr-structure-name});
+@end example
+
+@noindent
+@var{subr-structure-name} is the name you used as the third argument to
+@code{DEFUN}.
+
+  If you are adding a primitive to a file that already has Lisp
+primitives defined in it, find the function (near the end of the file)
+named @code{syms_of_@var{something}}, and add that function call to it.
+If the file doesn't have this function, or if you create a new file, add
+to it a @code{syms_of_@var{filename}} (e.g., @code{syms_of_myfile}).
+Then find the spot in @file{emacs.c} where all of these functions are
+called, and add a call to @code{syms_of_@var{filename}} there.
+
+  This function @code{syms_of_@var{filename}} is also the place to
+define any C variables which are to be visible as Lisp variables.
+@code{DEFVAR_LISP} is used to make a C variable of type
+@code{Lisp_Object} visible in Lisp.  @code{DEFVAR_INT} is used to make a
+C variable of type @code{int} visible in Lisp with a value that is an
+integer.
+
+  Here is another function, with more complicated arguments.  This comes
+from the code for the X Window System, and it demonstrates the use of
+macros and functions to manipulate Lisp objects.
+
+@smallexample
+@group
+DEFUN ("coordinates-in-window-p", Fcoordinates_in_window_p,
+  Scoordinates_in_window_p, 2, 2,
+  "xSpecify coordinate pair: \nXExpression which evals to window: ",
+  "Return non-nil if POSITIONS is in WINDOW.\n\  
+  \(POSITIONS is a list, (SCREEN-X SCREEN-Y)\)\n\
+@end group
+@group
+  Returned value is list of positions expressed\n\
+  relative to window upper left corner.")
+  (coordinate, window)
+     register Lisp_Object coordinate, window;
+@{
+  register Lisp_Object xcoord, ycoord;
+@end group
+
+@group
+  if (!CONSP (coordinate)) wrong_type_argument (Qlistp, coordinate);
+  CHECK_WINDOW (window, 2);
+  xcoord = Fcar (coordinate);
+  ycoord = Fcar (Fcdr (coordinate));
+  CHECK_NUMBER (xcoord, 0);
+  CHECK_NUMBER (ycoord, 1);
+@end group
+@group
+  if ((XINT (xcoord) < XINT (XWINDOW (window)->left))
+      || (XINT (xcoord) >= (XINT (XWINDOW (window)->left)
+                            + XINT (XWINDOW (window)->width))))
+    @{
+      return Qnil;
+    @}
+  XFASTINT (xcoord) -= XFASTINT (XWINDOW (window)->left);
+@end group
+@group
+  if (XINT (ycoord) == (screen_height - 1))
+    return Qnil;
+@end group
+@group
+  if ((XINT (ycoord) < XINT (XWINDOW (window)->top))
+      || (XINT (ycoord) >= (XINT (XWINDOW (window)->top)
+                            + XINT (XWINDOW (window)->height)) - 1))
+    @{
+      return Qnil;
+    @}
+@end group
+@group
+  XFASTINT (ycoord) -= XFASTINT (XWINDOW (window)->top);
+  return (Fcons (xcoord, Fcons (ycoord, Qnil)));
+@}
+@end group
+@end smallexample
+
+  Note that you cannot directly call functions defined in Lisp as, for
+example, the primitive function @code{Fcons} is called above.  You must
+create the appropriate Lisp form, protect everything from garbage
+collection, and @code{Feval} the form, as was done in @code{For} above.
+
+  @file{eval.c} is a very good file to look through for examples;
+@file{lisp.h} contains the definitions for some important macros and
+functions.
+
+@node Object Internals,  , Writing Emacs Primitives, GNU Emacs Internals
+@appendixsec Object Internals
+@cindex object internals
+
+  GNU Emacs Lisp manipulates many different types of data.  The actual
+data are stored in a heap and the only access that programs have to it is
+through pointers.  Pointers are thirty-two bits wide in most
+implementations.  Depending on the operating system and type of machine
+for which you compile Emacs, twenty-four to twenty-six bits are used to
+address the object, and the remaining six to eight bits are used for a
+tag that identifies the object's type.
+
+  Because all access to data is through tagged pointers, it is always
+possible to determine the type of any object.  This allows variables to
+be untyped, and the values assigned to them to be changed without regard
+to type.  Function arguments also can be of any type; if you want a
+function to accept only a certain type of argument, you must check the
+type explicitly using a suitable predicate (@pxref{Type Predicates}).
+@cindex type checking internals
+
+@menu
+* Buffer Internals::    Components of a buffer structure.
+* Window Internals::    Components of a window structure.
+* Process Internals::   Components of a process structure.
+@end menu
+
+@node Buffer Internals, Window Internals, Object Internals, Object Internals
+@appendixsubsec Buffer Internals
+@cindex internals, of buffer
+@cindex buffer internals
+
+  Buffers contain fields not directly accessible by the Lisp programmer.
+We describe them here, naming them by the names used in the C code.
+Many are accessible indirectly in Lisp programs via Lisp primitives.
+
+@table @code
+@item name
+The buffer name is a string which names the buffer.  It is guaranteed to
+be unique.  @xref{Buffer Names}.
+
+@item save_modified
+This field contains the time when the buffer was last saved, as an integer.
+@xref{Buffer Modification}.
+
+@item modtime
+This field contains the modification time of the visited file.  It is
+set when the file is written or read.  Every time the buffer is written
+to the file, this field is compared to the modification time of the
+file.  @xref{Buffer Modification}.
+
+@item auto_save_modified
+This field contains the time when the buffer was last auto-saved.
+
+@item last_window_start
+This field contains the @code{window-start} position in the buffer as of
+the last time the buffer was displayed in a window.
+
+@item undodata
+This field points to the buffer's undo stack.  @xref{Undo}.
+
+@item syntax_table_v
+This field contains the syntax table for the buffer.  @xref{Syntax Tables}.
+
+@item downcase_table
+This field contains the conversion table for converting text to lower case.
+@xref{Case Table}.
+
+@item upcase_table
+This field contains the conversion table for converting text to upper case.
+@xref{Case Table}.
+
+@item case_canon_table
+This field contains the conversion table for canonicalizing text for
+case-folding search.  @xref{Case Table}.
+
+@item case_eqv_table
+This field contains the equivalence table for case-folding search.
+@xref{Case Table}.
+
+@item display_table
+This field contains the buffer's display table, or @code{nil} if it doesn't
+have one.  @xref{Display Tables}.
+
+@item markers
+This field contains the chain of all markers that point into the
+buffer.  At each deletion or motion of the buffer gap, all of these
+markers must be checked and perhaps updated.  @xref{Markers}.
+
+@item backed_up
+This field is a flag which tells whether a backup file has been made
+for the visited file of this buffer.
+
+@item mark
+This field contains the mark for the buffer.  The mark is a marker,
+hence it is also included on the list @code{markers}.  @xref{The Mark}.
+
+@item local_var_alist
+This field contains the association list containing all of the variables
+local in this buffer, and their values.  The function
+@code{buffer-local-variables} returns a copy of this list.
+@xref{Buffer-Local Variables}.
+
+@item mode_line_format
+This field contains a Lisp object which controls how to display the mode
+line for this buffer.  @xref{Mode Line Format}.
+@end table
+
+@node Window Internals, Process Internals, Buffer Internals, Object Internals
+@appendixsubsec Window Internals
+@cindex internals, of window
+@cindex window internals
+
+  Windows have the following accessible fields:
+
+@table @code
+@item frame
+  The frame that this window is on.
+
+@item mini_p
+  Non-@code{nil} if this window is a minibuffer window.
+
+@item height
+  The height of the window, measured in lines.
+
+@item width
+  The width of the window, measured in columns.
+
+@item buffer
+  The buffer which the window is displaying.  This may change often during
+the life of the window.
+
+@item dedicated
+  Non-@code{nil} if this window is dedicated to its buffer.
+
+@item start
+ The position in the buffer which is the first character to be displayed
+in the window.
+
+@item pointm
+@cindex window point internals
+  This is the value of point in the current buffer when this window is
+selected; when it is not selected, it retains its previous value.
+
+@item left
+  This is the left-hand edge of the window, measured in columns.  (The
+leftmost column on the screen is @w{column 0}.)
+
+@item top
+  This is the top edge of the window, measured in lines.  (The top line on
+the screen is @w{line 0}.)
+
+@item next
+  This is the window that is the next in the chain of siblings.
+
+@item prev
+  This is the window that is the previous in the chain of siblings.
+
+@item force_start
+  This is a flag which, if non-@code{nil}, says that the window has been
+scrolled explicitly by the Lisp program.  At the next redisplay, if
+point is off the screen, instead of scrolling the window to show the
+text around point, point will be moved to a location that is on the
+screen.
+
+@item hscroll
+  This is the number of columns that the display in the window is scrolled
+horizontally to the left.  Normally, this is 0.
+
+@item use_time
+  This is the last time that the window was selected.  The function
+@code{get-lru-window} uses this field.
+
+@item display_table
+  The window's display table, or @code{nil} if none is specified for it.
+@end table
+
+@node Process Internals,  , Window Internals, Object Internals
+@appendixsubsec Process Internals
+@cindex internals, of process
+@cindex process internals
+
+  The fields of a process are:
+
+@table @code
+@item name
+A string, the name of the process.
+
+@item command
+A list containing the command arguments that were used to start this
+process.
+
+@item filter
+A function used to accept output from the process instead of a buffer,
+or @code{nil}.
+
+@item sentinel
+A function called whenever the process receives a signal, or @code{nil}.
+
+@item buffer
+The associated buffer of the process.
+
+@item pid
+An integer, the Unix process @sc{id}.
+
+@item childp
+A flag, non-@code{nil} if this is really a child process.
+It is @code{nil} for a network connection.
+
+@item flags
+A symbol indicating the state of the process.  Possible values include
+@code{run}, @code{stop}, @code{closed}, etc.
+
+@item reason
+An integer, the Unix signal number that the process received that
+caused the process to terminate or stop.  If the process has exited,
+then this is the exit code it specified.
+
+@item mark
+A marker indicating the position of end of last output from this process
+inserted into the buffer.  This is usually the end of the buffer.
+
+@item kill_without_query
+A flag, non-@code{nil} meaning this process should not cause
+confirmation to be needed if Emacs is killed.
+@end table