For those users who live backwards in time, here is information about downgrading to Emacs version 20. We hope you will enjoy the greater simplicity that results from the absence of many Emacs 21 features.
The display engine has been greatly simplified by eliminating support for variable-size characters and other non-text display features. This avoids the complexity of display layout in Emacs 21. To wit:
Variable-size characters are not supported in Emacs 20. You cannot use fonts which contain oversized characters, and using italics fonts can result in illegible display. However, text which uses variable-size fonts is unreadable anyway. With all characters in a frame layed out on a regular grid, each character having the same height and width, text is much easier to read.
Emacs does not display images, or play sounds. It just displays text, as you would expect from a text editor.
Specification of the font for a face now uses an XLFD font name, for compatibility with other X applications. This means that font attributes cannot be merged when combining faces; however, experience shows that mergers are bad economics. Face inheritance has also been removed, so no one can accumulate "too much face."
Several face appearance attributes such as 3D appearence, strike-through, and overline, have been eliminated.
Emacs now provides its own "lean and mean" scroll bars instead of using those from the X toolkit. Toggle buttons and radio buttons in menus now look just like any other menu item, which simplifies them, and prevents them from standing out and distracting your attention from the other menu items.
There are no toolbars and no tooltips; in particular, GUD mode cannot display variable values in a tooltip when you click on that variable's name. Instead, Emacs 20 provides a direct interface to the debugger, so that you can type appropriate debugger commands, such as display foo and print bar. As these commands use explicit words, their meaning is more self-evident.
Colors are not available on character terminals. If you must have colors, but cannot afford running X, you can now use the MS-DOG version of Emacs inside a DOS emulator.
The mode line is not mouse-sensitive, since it is meant only to display information. Use keyboard commands to switch between buffers, toggle read-only and modified status, switch minor modes on and off, etc.
The support for "wheeled" mice under X has been removed, because of their slow scroll rate, and because you will find less and less of these mice as you go back in time. Instead Emacs 20 provides the C-v and M-v keys for scrolling. (You can also use the scroll bar, but be advised that it, too, may be absent in yet earlier Emacs versions.)
Busy-cursor display is gone, as it was found to be too hard to draw on displays whose resolution is getting lower and lower. This means that you get the standard kind of cursor blinking that your terminal provides.
Some aspects of Emacs appearance, such as the colors of the scroll bar and the menus, can only be controlled via X resources. Since colors aren't supported except on X, it doesn't make any sense doing this in any way but the X way. For those users who aren't privy to X arcana, we've provided good default colors that should make everybody happy.
The variable show-trailing-whitespace has no special meaning, so trailing whitespace on a line is now always displayed correctly: as empty space. To see if a line ends with spaces or TABs, type C-e on that line. Likewise, empty lines at the end of the buffer are not marked in any way; use M-> to see where the end of the buffer is.
The spacing between text lines on the display now always follows the font design and the rules of your window manager. This provides for predictable appearance of the displayed text.
Emacs 20 has simpler support for multi-lingual editing. While not as radical a simplification as Emacs 19 was, it goes a long way toward eliminating some of the annoying features:
Translations of the Emacs reference cards to other languages are no longer part of the distribution, because in the past we expect computer users to speak English.
To avoid extra confusion, many language environments have been eliminated. For example, Polish and Celtic (Latin-8) environments are not supported. The Latin-9 environment is gone, too, because you won't need the Euro sign in the past.
Emacs 20 always asks you which coding system to use when saving a buffer, unless it can use the same one that it used to read the buffer. It does not try to see if the preferred coding system is suitable.
Commands which provide detailed information about character sets and coding systems, such as list-charset-chars, describe-character-set, and the C-u C-x = key-sequence, no longer exist. The less said about non-ascii characters, the better.
The terminal coding system cannot be set to something CCL-based, so keyboards which produce KOI8 and DOS/Windows codepage codes cannot be supported directly. Instead, you should use one of the input methods provided in the Leim package.
As you move back through time, some systems will become unimportant or enter the vaporware phase, so Emacs 20 does not support them:
Emacs 20 cannot be built on GNU/Linux systems running on IA64 machines, and you cannot build a 64-bit Emacs on Solaris or Irix even though there are still 64-bit versions of those OSes.
LynxOS is also not supported, and neither is the Macintosh, though they still exist.
The arrangement of menu bar items differs from most other GUI programs. We think that uniformity of look-and-feel is boring, and that Emacs' unique features require its unique menu-bar configuration.
You cannot save the options that you set from the Options menu-bar menu; instead, you need to set all the options again each time you start a new session. However, if you follow the recommended practice and keep a single Emacs session running until you log out, you won't have to set the options very often.
Emacs 20 does not pop up a buffer with error messages when an error is signaled during loading of the user's init file. Instead, it simply announces the fact that an error happened. To know where in the init file was that, insert (message "foo") lines judiciously into the file and look for those messages in the *Messages* buffer.
Some commands no longer treat Transient Mark mode specially. For example, ispell doesn't spell-check the region when Transient Mark mode is in effect and the mark is active; instead, it checks the current buffer. (Transient Mark mode is alien to the spirit of Emacs, so we are planning to remove it altogether in an earlier version.)
C-Down-Mouse-3 does not show what would be in the menu bar when the menu bar is not displayed.
For uniformity, the delete function key in Emacs 20 works exactly like the DEL key, on both text-only terminals and window systems--it always deletes backward. This eliminates the inconsistency of Emacs 21, where the key labeled delete deletes forward when you are using a window system, and backward on a text-only terminals.
The ability to place backup files in special subdirectories (controlled by backup-directory-alist) has been eliminated. This makes finding your backup files much easier: they are always in the same directory as the original files.
Emacs no longer refuses to load Lisp files compiled by incompatible versions of Emacs, which may contain invalid byte-code. Instead, Emacs now dumps core when it encounters such byte-code. However, this is a rare occurrence, and it won't happen at all when all Emacs versions merge together, in the distant past.
The C-x 5 1 command has been eliminated. If you want to delete all the frames but the current one, delete them one by one instead.
CC Mode now enforces identical values for some customizable options, such as indentation style, for better consistency. In particular, if you select an indentation style for Java, the same style is used for C and C++ buffers as well.
Isearch does not highlight other possible matches; it shows only the current match, to avoid distracting your attention. Mouse-2 in the echo area during incremental search now signals an error, instead of inserting the current selection into the search string. But you can accomplish more or less the same job by typing M-y.
The ability to specify a port number when editing remote files with ange-ftp was removed. Instead, Emacs 20 provides undocumented features in the function ange-ftp-normal-login ([Use the source, Luke!]) to specify the port.
Emacs 20 does not check for changing time stamps of remote files, since the old FTP programs you will encounter in the past could not provide the time stamp anyway. Windows-style FTP clients which output the ^M character at the end of each line get special handling from ange-ftp in Emacs 20, with unexpected results that should make your life more interesting.
Many complicated display features, including highlighting of mouse-sensitive text regions and popping up help strings for menu items, don't work in the MS-DOS version. Spelling doesn't work on MS-DOS, and Eshell doesn't exist, so there's no workable shell-mode, either. This fits the spirit of MS-DOS, which resembles a dumb character terminal.
The woman package has been removed, so Emacs users on non-Posix systems will need a real man to read manual pages. (Users who are not macho can read the Info documentation instead.)
recentf has been removed, because we figure that you can remember the names of the files you edit frequently. With decreasing disk size, you should have fewer files anyway, so you won't notice the absence of this feature.
The field property does not exist in Emacs 20, so various packages that run subsidiary programs in Emacs buffers cannot in general distinguish which text was user input and which was output from the subprocess. If you need to try to do this nonetheless, Emacs 20 provides a variable comint-prompt-regexp, which lets you try to distinguish input by recognizing prompt strings.
We have eliminated the special major modes for Delphi sources, PostScript files, context diffs, and TODO files. Use Fundamental Mode instead.
Many additional packages that unnecessarily complicate your life in Emacs 21 are absent in Emacs 20. You cannot browse C++ classes with Ebrowse, access SQL data bases, access LDAP and other directory servers, or mix shell commands and Lisp functions using Eshell.
To keep up with decreasing computer memory capacity and disk space, many other functions and files have been eliminated in Emacs 20.