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Glossary

Abbrev
An abbrev is a text string which expands into a different text string when present in the buffer. For example, you might define a short word as an abbrev for a long phrase that you want to insert frequently. See section Abbrevs.

Aborting
Aborting means getting out of a recursive edit (q.v.). The commands C-] and M-x top-level are used for this. See section Quitting and Aborting.

Alt
Alt is the name of a modifier bit which a keyboard input character may have. To make a character Alt, type it while holding down the ALT key. Such characters are given names that start with Alt- (usually written A- for short). See section Keyboard Input.

Auto Fill Mode
Auto Fill mode is a minor mode in which text that you insert is automatically broken into lines of fixed width. See section Filling Text.

Auto Saving
Auto saving is the practice of saving the contents of an Emacs buffer in a specially-named file, so that the information will not be lost if the buffer is lost due to a system error or user error. See section Auto-Saving: Protection Against Disasters.

Backup File
A backup file records the contents that a file had before the current editing session. Emacs makes backup files automatically to help you track down or cancel changes you later regret making. See section Backup Files.

Balance Parentheses
Emacs can balance parentheses manually or automatically. Manual balancing is done by the commands to move over balanced expressions (see section Lists and Sexps). Automatic balancing is done by blinking the parenthesis that matches one just inserted (see section Automatic Display Of Matching Parentheses).

Bind
To bind a key sequence means to give it a binding (q.v.). See section Changing Key Bindings Interactively.

Binding
A key sequence gets its meaning in Emacs by having a binding, which is a command (q.v.), a Lisp function that is run when the user types that sequence. See section Keys and Commands. Customization often involves rebinding a character to a different command function. The bindings of all key sequences are recorded in the keymaps (q.v.). See section Keymaps.

Blank Lines
Blank lines are lines that contain only whitespace. Emacs has several commands for operating on the blank lines in the buffer.

Buffer
The buffer is the basic editing unit; one buffer corresponds to one piece of text being edited. You can have several buffers, but at any time you are editing only one, the `selected' buffer, though several can be visible when you are using multiple windows. See section Using Multiple Buffers.

Buffer Selection History
Emacs keeps a buffer selection history which records how recently each Emacs buffer has been selected. This is used for choosing a buffer to select. See section Using Multiple Buffers.

Button Down Event
A button down event is the kind of input event generated right away when you press a mouse button. See section Rebinding Mouse Buttons.

C-
`C' in the name of a character is an abbreviation for Control. See section Keyboard Input.

C-M-
`C-M-' in the name of a character is an abbreviation for Control-Meta. See section Keyboard Input.

Case Conversion
Case conversion means changing text from upper case to lower case or vice versa. See section Case Conversion Commands, for the commands for case conversion.

Characters
Characters form the contents of an Emacs buffer; see section Character Set for Text. Also, key sequences (q.v.) are usually made up of characters (though they may include other input events as well). See section Keyboard Input.

Click Event
A click event is the kind of input event generated when you press a mouse button and let it go without moving the mouse. See section Rebinding Mouse Buttons.

Command
A command is a Lisp function specially defined to be able to serve as a key binding in Emacs. When you type a key sequence (q.v.), its binding (q.v.) is looked up in the relevant keymaps (q.v.) to find the command to run. See section Keys and Commands.

Command Name
A command name is the name of a Lisp symbol which is a command (see section Keys and Commands). You can invoke any command by its name using M-x (see section Running Commands by Name).

Comments
A comment is text in a program which is intended only for humans reading the program, and which is marked specially so that it will be ignored when the program is loaded or compiled. Emacs offers special commands for creating, aligning and killing comments. See section Manipulating Comments.

Compilation
Compilation is the process of creating an executable program from source code. Emacs has commands for compiling files of Emacs Lisp code (see section `Byte Compilation' in the Emacs Lisp Reference Manual) and programs in C and other languages (see section Running `make', or Compilers Generally).

Complete Key
A complete key is a key sequence which fully specifies one action to be performed by Emacs. For example, X and C-f and C-x m are complete keys. Complete keys derive their meanings from being bound (q.v.) to commands (q.v.). Thus, X is conventionally bound to a command to insert `X' in the buffer; C-x m is conventionally bound to a command to begin composing a mail message. See section Keys.

Completion
Completion is what Emacs does when it automatically fills out an abbreviation for a name into the entire name. Completion is done for minibuffer (q.v.) arguments when the set of possible valid inputs is known; for example, on command names, buffer names, and file names. Completion occurs when TAB, SPC or RET is typed. See section Completion.

Continuation Line
When a line of text is longer than the width of the window, it takes up more than one screen line when displayed. We say that the text line is continued, and all screen lines used for it after the first are called continuation lines. See section Basic Editing Commands.

Control Character
ASCII characters with octal codes 0 through 037, and also code 0177, do not have graphic images assigned to them. These are the Control characters. To type a Control character, hold down the CTRL key and type the corresponding non-Control character. RET, TAB, ESC, LFD and DEL are all control characters. See section Keyboard Input.

When you are using the X Window System, every non-control character has a corresponding control character variant.

Copyleft
A copyleft is a notice giving the public legal permission to redistribute a program or other work of art. Copylefts are used by left-wing programmers to give people equal rights, just as copyrights are used by right-wing programmers to gain power over other people.

Current Buffer
The current buffer in Emacs is the Emacs buffer on which most editing commands operate. You can select any Emacs buffer as the current one. See section Using Multiple Buffers.

Current Line
The line point is on (see section Point).

Current Paragraph
The paragraph that point is in. If point is between paragraphs, the current paragraph is the one that follows point. See section Paragraphs.

Current Defun
The defun (q.v.) that point is in. If point is between defuns, the current defun is the one that follows point. See section Defuns.

Cursor
The cursor is the rectangle on the screen which indicates the position called point (q.v.) at which insertion and deletion takes place. The cursor is on or under the character that follows point. Often people speak of `the cursor' when, strictly speaking, they mean `point'. See section Basic Editing Commands.

Customization
Customization is making minor changes in the way Emacs works. It is often done by setting variables (see section Variables) or by rebinding key sequences (see section Keymaps).

Default Argument
The default for an argument is the value that will be assumed if you do not specify one. When the minibuffer is used to read an argument, the default argument is used if you just type RET. See section The Minibuffer.

Default Directory
When you specify a file name that does not start with `/' or `~', it is interpreted relative to the current buffer's default directory. See section Minibuffers for File Names.

Defun
A defun is a list at the top level of parenthesis or bracket structure in a program. It is so named because most such lists in Lisp programs are calls to the Lisp function defun. See section Defuns.

DEL
DEL is a character that runs the command to delete one character of text. See section Basic Editing Commands.

Deletion
Deletion means erasing text without copying it into the kill ring (q.v.). The alternative is killing (q.v.). See section Deletion and Killing.

Deletion of Files
Deleting a file means erasing it from the file system. See section Miscellaneous File Operations.

Deletion of Messages
Deleting a message means flagging it to be eliminated from your mail file. Until you expunge (q.v.) the mail file, you can still undelete the messages you have deleted. See section Deleting Messages.

Deletion of Windows
Deleting a window means eliminating it from the screen. Other windows expand to use up the space. The deleted window can never come back, but no actual text is thereby lost. See section Multiple Windows.

Directory
File directories are named collections in the file system, within which you can place individual files or subdirectories. See section Listing a File Directory.

Dired
Dired is the Emacs facility that displays the contents of a file directory and allows you to "edit the directory", performing operations on the files in the directory. See section Dired, the Directory Editor.

Disabled Command
A disabled command is one that you may not run without special confirmation. The usual reason for disabling a command is that it is confusing for beginning users. See section Disabling Commands.

Down Event
Short for `button down event'.

Drag Event
A drag event is the kind of input event generated when you press a mouse button, move the mouse, and then release the button. See section Rebinding Mouse Buttons.

Dribble File
A file into which Emacs writes all the characters that the user types on the keyboard. Dribble files are used to make a record for debugging Emacs bugs. Emacs does not make a dribble file unless you tell it to. See section Reporting Bugs.

Echo Area
The echo area is the bottom line of the screen, used for echoing the arguments to commands, for asking questions, and printing brief messages (including error messages). See section The Echo Area.

Echoing
Echoing is acknowledging the receipt of commands by displaying them (in the echo area). Emacs never echoes single-character key sequences; longer key sequences echo only if you pause while typing them.

Error
An error occurs when an Emacs command cannot execute in the current circumstances. When an error occurs, execution of the command stops (unless the command has been programmed to do otherwise) and Emacs reports the error by printing an error message (q.v.). Type-ahead is discarded. Then Emacs is ready to read another editing command.

Error Messages
Error messages are single lines of output printed by Emacs when the user asks for something impossible to do (such as, killing text forward when point is at the end of the buffer). They appear in the echo area, accompanied by a beep.

ESC
ESC is a character used as a prefix for typing Meta characters on keyboards lacking a META key. Unlike the META key (which, like the SHIFT key, is held down while another character is typed), the ESC key is pressed once and applies to the next character typed.

Expunging
Expunging a mail file or Dired buffer means really discarding the messages or files you have previously flagged for deletion.

File Name
A file name is a name that refers to a file. File names may be relative or absolute; the meaning of a relative file name depends on the current directory, but an absolute file name refers to the same file regardless of which directory is current. On GNU and Unix systems, an absolute file name starts with a slash (the root directory) or with `~/' or `~user/' (a home directory).

Some people use the term "pathname" for file names, but we do not; we use the word "path" only in the term "search path" (q.v.).

File Name Component
A file name component names a file directly within a particular directory. On GNU and Unix systems, a file name is a sequence of file name components, separated by slashes. For example, `foo/bar' is a file name containing two components, `foo' and `bar'; it refers to the file named `bar' in the directory named `foo' in the current directory.

Fill Prefix
The fill prefix is a string that should be expected at the beginning of each line when filling is done. It is not regarded as part of the text to be filled. See section Filling Text.

Filling
Filling text means moving text from line to line so that all the lines are approximately the same length. See section Filling Text.

Frame
A frame is a rectangular cluster of Emacs windows. When using X Windows, you can create more than one Emacs frame, each having its own X window, and then you can subdivide each frame into Emacs windows as you wish. See section Frames and X Windows.

Function Key
A function key is a key on the keyboard that does not correspond to any character. See section Rebinding Function Keys.

Global
Global means `independent of the current environment; in effect throughout Emacs'. It is the opposite of local (q.v.). Particular examples of the use of `global' appear below.

Global Abbrev
A global definition of an abbrev (q.v.) is effective in all major modes that do not have local (q.v.) definitions for the same abbrev. See section Abbrevs.

Global Keymap
The global keymap (q.v.) contains key bindings that are in effect except when overridden by local key bindings in a major mode's local keymap (q.v.). See section Keymaps.

Global Substitution
Global substitution means replacing each occurrence of one string by another string through a large amount of text. See section Replacement Commands.

Global Variable
The global value of a variable (q.v.) takes effect in all buffers that do not have their own local (q.v.) values for the variable. See section Variables.

Graphic Character
Graphic characters are those assigned pictorial images rather than just names. All the non-Meta (q.v.) characters except for the Control (q.v.) characters are graphic characters. These include letters, digits, punctuation, and spaces; they do not include RET or ESC. In Emacs, typing a graphic character inserts that character (in ordinary editing modes). See section Basic Editing Commands.

Hardcopy
Hardcopy means printed output. Emacs has commands for making printed listings of text in Emacs buffers. See section Hardcopy Output.

HELP
You can type HELP at any time to ask what options you have, or to ask what any command does. The character HELP is really C-h. See section Help.

Hyper
Hyper is the name of a modifier bit which a keyboard input character may have. To make a character Hyper, type it while holding down the HYPER key. Such characters are given names that start with Hyper- (usually written H- for short). See section Keyboard Input.

Inbox
An inbox is a file in which mail is delivered by the operating system. Rmail transfers mail from inboxes to mail files (q.v.) in which the mail is then stored permanently or until explicitly deleted. See section Rmail Files and Inboxes.

Indentation
Indentation means blank space at the beginning of a line. Most programming languages have conventions for using indentation to illuminate the structure of the program, and Emacs has special commands to adjust indentation. See section Indentation.

Insertion
Insertion means copying text into the buffer, either from the keyboard or from some other place in Emacs.

Justification
Justification means adding extra spaces to lines of text to make them come exactly to a specified width. See section Filling Text.

Keyboard Macros
Keyboard macros are a way of defining new Emacs commands from sequences of existing ones, with no need to write a Lisp program. See section Keyboard Macros.

Key Sequence
A key sequence (key, for short) is a sequence of characters that, when input to Emacs, is meaningful as a single unit. If the key sequence is enough to specify one action, it is a complete key (q.v.); if it is not enough, it is a prefix key (q.v.). See section Keys.

Keymap
The keymap is the data structure that records the bindings (q.v.) of key sequences to the commands that they run. For example, the global keymap binds the character C-n to the command function next-line. See section Keymaps.

Keyboard Translation Table
The keyboard translation table is an array that translates the character codes that come from the terminal into the character codes that make up key sequences. See section Keyboard Translations.

Kill Ring
The kill ring is where all text you have killed recently is saved. You can reinsert any of the killed text still in the ring; this is called yanking (q.v.). See section Yanking.

Killing
Killing means erasing text and saving it on the kill ring so it can be yanked (q.v.) later. Some other systems call this "cutting". Most Emacs commands to erase text do killing, as opposed to deletion (q.v.). See section Deletion and Killing.

Killing Jobs
Killing a job (such as, an invocation of Emacs) means making it cease to exist. Any data within it, if not saved in a file, is lost. See section Exiting Emacs.

List
A list is, approximately, a text string beginning with an open parenthesis and ending with the matching close parenthesis. In C mode and other non-Lisp modes, groupings surrounded by other kinds of matched delimiters appropriate to the language, such as braces, are also considered lists. Emacs has special commands for many operations on lists. See section Lists and Sexps.

Local
Local means `in effect only in a particular context'; the relevant kind of context is a particular function execution, a particular buffer, or a particular major mode. It is the opposite of `global' (q.v.). Specific uses of `local' in Emacs terminology appear below.

Local Abbrev
A local abbrev definition is effective only if a particular major mode is selected. In that major mode, it overrides any global definition for the same abbrev. See section Abbrevs.

Local Keymap
A local keymap is used in a particular major mode; the key bindings (q.v.) in the current local keymap override global bindings of the same key sequences. See section Keymaps.

Local Variable
A local value of a variable (q.v.) applies to only one buffer. See section Local Variables.

M-
M- in the name of a character is an abbreviation for META, one of the modifier keys that can accompany any character. See section Keyboard Input.

M-C-
`M-C-' in the name of a character is an abbreviation for Control-Meta; it means the same thing as `C-M-'. If your terminal lacks a real META key, you type a Control-Meta character by typing ESC and then typing the corresponding Control character. See section Keyboard Input.

M-x
M-x is the key sequence which is used to call an Emacs command by name. This is how you run commands that are not bound to key sequences. See section Running Commands by Name.

Mail
Mail means messages sent from one user to another through the computer system, to be read at the recipient's convenience. Emacs has commands for composing and sending mail, and for reading and editing the mail you have received. See section Sending Mail. See section Reading Mail with Rmail, for how to read mail.

Mail File
A mail file is a file which is edited using Rmail and in which Rmail stores mail. See section Reading Mail with Rmail.

Major Mode
The Emacs major modes are a mutually exclusive set of options, each of which configures Emacs for editing a certain sort of text. Ideally, each programming language has its own major mode. See section Major Modes.

Mark
The mark points to a position in the text. It specifies one end of the region (q.v.), point being the other end. Many commands operate on all the text from point to the mark. Each buffer has its own mark. See section The Mark and the Region.

Mark Ring
The mark ring is used to hold several recent previous locations of the mark, just in case you want to move back to them. Each buffer has its own mark ring. See section The Mark Ring.

Message
See `mail'.

Meta
Meta is the name of a modifier bit which a command character may have. It is present in a character if the character is typed with the META key held down. Such characters are given names that start with Meta- (usually written M- for short). For example, M-< is typed by holding down META and at the same time typing < (which itself is done, on most terminals, by holding down SHIFT and typing ,). See section Keyboard Input.

Meta Character
A Meta character is one whose character code includes the Meta bit.

Minibuffer
The minibuffer is the window that appears when necessary inside the echo area (q.v.), used for reading arguments to commands. See section The Minibuffer.

Minibuffer History
The minibuffer history records the text you have specified in the past for minibuffer arguments, so you can conveniently use the same text again. See section Minibuffer History.

Minor Mode
A minor mode is an optional feature of Emacs which can be switched on or off independently of all other features. Each minor mode has a command to turn it on or off. See section Minor Modes.

Minor Mode Keymap
A keymap that belongs to a minor mode and is active when that mode is enabled. Minor mode keymaps take precedence over the buffer's local keymap, just as the local keymap takes precedence over the global keymap. See section Keymaps.

Mode Line
The mode line is the line at the bottom of each window (q.v.), giving status information on the buffer displayed in that window. See section The Mode Line.

Modified Buffer
A buffer (q.v.) is modified if its text has been changed since the last time the buffer was saved (or since when it was created, if it has never been saved). See section Saving Files.

Moving Text
Moving text means erasing it from one place and inserting it in another. The usual way to move text by killing (q.v.) and then yanking (q.v.). See section Deletion and Killing.

Named Mark
A named mark is a register (q.v.) in its role of recording a location in text so that you can move point to that location. See section Registers.

Narrowing
Narrowing means creating a restriction (q.v.) that limits editing in the current buffer to only a part of the text in the buffer. Text outside that part is inaccessible to the user until the boundaries are widened again, but it is still there, and saving the file saves it all. See section Narrowing.

Newline
LFD characters in the buffer terminate lines of text and are called newlines. See section Character Set for Text.

Numeric Argument
A numeric argument is a number, specified before a command, to change the effect of the command. Often the numeric argument serves as a repeat count. See section Numeric Arguments.

Option
An option is a variable (q.v.) that exists so that you can customize Emacs by giving it a new value. See section Variables.

Overwrite Mode
Overwrite mode is a minor mode. When it is enabled, ordinary text characters replace the existing text after point rather than pushing it to the right. See section Minor Modes.

Page
A page is a unit of text, delimited by formfeed characters (ASCII control-L, code 014) coming at the beginning of a line. Some Emacs commands are provided for moving over and operating on pages. See section Pages.

Paragraphs
Paragraphs are the medium-size unit of English text. There are special Emacs commands for moving over and operating on paragraphs. See section Paragraphs.

Parsing
We say that certain Emacs commands parse words or expressions in the text being edited. Really, all they know how to do is find the other end of a word or expression. See section The Syntax Table.

Point
Point is the place in the buffer at which insertion and deletion occur. Point is considered to be between two characters, not at one character. The terminal's cursor (q.v.) indicates the location of point. See section Basic Editing Commands.
Prefix Argument
See `numeric argument'.

Prefix Key
A prefix key is a key sequence (q.v.) whose sole function is to introduce a set of longer key sequences. C-x is an example of prefix key; any two-character sequence starting with C-x is therefore a legitimate key sequence. See section Keys.

Primary Mail File
Your primary mail file is the file named `RMAIL' in your home directory, where all mail that you receive is stored by Rmail unless you make arrangements to do otherwise. See section Reading Mail with Rmail.

Prompt
A prompt is text printed to ask the user for input. Printing a prompt is called prompting. Emacs prompts always appear in the echo area (q.v.). One kind of prompting happens when the minibuffer is used to read an argument (see section The Minibuffer); the echoing which happens when you pause in the middle of typing a multicharacter key sequence is also a kind of prompting (see section The Echo Area).

Quitting
Quitting means cancelling a partially typed command or a running command, using C-g. See section Quitting and Aborting.

Quoting
Quoting means depriving a character of its usual special significance. In Emacs this is usually done with C-q. What constitutes special significance depends on the context and on convention. For example, an "ordinary" character as an Emacs command inserts itself; so in this context, a special character is any character that does not normally insert itself (such as DEL, for example), and quoting it makes it insert itself as if it were not special. Not all contexts allow quoting. See section Basic Editing Commands.

Read-Only Buffer
A read-only buffer is one whose text you are not allowed to change. Normally Emacs makes buffers read-only when they contain text which has a special significance to Emacs; for example, Dired buffers. Visiting a file that is write protected also makes a read-only buffer. See section Using Multiple Buffers.

Recursive Editing Level
A recursive editing level is a state in which part of the execution of a command involves asking the user to edit some text. This text may or may not be the same as the text to which the command was applied. The mode line indicates recursive editing levels with square brackets (`[' and `]'). See section Recursive Editing Levels.

Redisplay
Redisplay is the process of correcting the image on the screen to correspond to changes that have been made in the text being edited. See section The Organization of the Screen.

Regexp
See `regular expression'.

Region
The region is the text between point (q.v.) and the mark (q.v.). Many commands operate on the text of the region. See section The Mark and the Region.

Registers
Registers are named slots in which text or buffer positions or rectangles can be saved for later use. See section Registers.

Regular Expression
A regular expression is a pattern that can match various text strings; for example, `l[0-9]+' matches `l' followed by one or more digits. See section Syntax of Regular Expressions.

Repeat Count
See `numeric argument'.

Replacement
See `global substitution'.

Restriction
A buffer's restriction is the amount of text, at the beginning or the end of the buffer, that is temporarily inaccessible. Giving a buffer a nonzero amount of restriction is called narrowing (q.v.). See section Narrowing.

RET
RET is a character than in Emacs runs the command to insert a newline into the text. It is also used to terminate most arguments read in the minibuffer (q.v.). See section Keyboard Input.

Saving
Saving a buffer means copying its text into the file that was visited (q.v.) in that buffer. This is the way text in files actually gets changed by your Emacs editing. See section Saving Files.

Scrolling
Scrolling means shifting the text in the Emacs window so as to see a different part of the buffer. See section Controlling the Display.

Searching
Searching means moving point to the next occurrence of a specified string. See section Searching and Replacement.

Search Path
A search path is a list of directory names, to be used for searching for files for certain purposes. For example, the variable load-path holds a search path for finding Lisp library files.

Selecting
Selecting a buffer means making it the current (q.v.) buffer. See section Using Multiple Buffers.

Self-Documentation
Self-documentation is the feature of Emacs which can tell you what any command does, or give you a list of all commands related to a topic you specify. You ask for self-documentation with the help character, C-h. See section Help.

Sentences
Emacs has commands for moving by or killing by sentences. See section Sentences.

Sexp
A sexp (short for `s-expression') is the basic syntactic unit of Lisp in its textual form: either a list, or Lisp atom. Many Emacs commands operate on sexps. The term `sexp' is generalized to languages other than Lisp, to mean a syntactically recognizable expression. See section Lists and Sexps.

Simultaneous Editing
Simultaneous editing means two users modifying the same file at once. Simultaneous editing if not detected can cause one user to lose his work. Emacs detects all cases of simultaneous editing and warns the user to investigate them. See section Protection against Simultaneous Editing.

String
A string is a kind of Lisp data object which contains a sequence of characters. Many Emacs variables are intended to have strings as values. The Lisp syntax for a string consists of the characters in the string with a `"' before and another `"' after. A `"' that is part of the string must be written as `\"' and a `\' that is part of the string must be written as `\\'. All other characters, including newline, can be included just by writing them inside the string; however, escape sequences as in C, such as `\n' for newline or `\241' using an octal character code, are allowed as well.

String Substitution
See `global substitution'.

Syntax Table
The syntax table tells Emacs which characters are part of a word, which characters balance each other like parentheses, etc. See section The Syntax Table.

Super
Super is the name of a modifier bit which a keyboard input character may have. To make a character Super, type it while holding down the SUPER key. Such characters are given names that start with Super- (usually written s- for short). See section Keyboard Input.

Tag Table
A tag table is a file that serves as an index to the function definitions in one or more other files. See section Tag Tables.

Termscript File
A termscript file contains a record of all characters sent by Emacs to the terminal. It is used for tracking down bugs in Emacs redisplay. Emacs does not make a termscript file unless you tell it to. See section Reporting Bugs.

Text
Two meanings (see section Commands for Human Languages):

Top Level
Top level is the normal state of Emacs, in which you are editing the text of the file you have visited. You are at top level whenever you are not in a recursive editing level (q.v.) or the minibuffer (q.v.), and not in the middle of a command. You can get back to top level by aborting (q.v.) and quitting (q.v.). See section Quitting and Aborting.

Transposition
Transposing two units of text means putting each one into the place formerly occupied by the other. There are Emacs commands to transpose two adjacent characters, words, sexps (q.v.) or lines (see section Transposing Text).

Truncation
Truncating text lines in the display means leaving out any text on a line that does not fit within the right margin of the window displaying it. See also `continuation line'. See section Basic Editing Commands.

Undoing
Undoing means making your previous editing go in reverse, bringing back the text that existed earlier in the editing session. See section Undoing Changes.

Variable
A variable is an object in Lisp that can store an arbitrary value. Emacs uses some variables for internal purposes, and has others (known as `options' (q.v.)) just so that you can set their values to control the behavior of Emacs. The variables used in Emacs that you are likely to be interested in are listed in the Variables Index in this manual. See section Variables, for information on variables.

Version Control
Version control systems keep track of multiple versions of a source file. They provide a more powerful alternative to keeping backup files (q.v.). See section Version Control.

Visiting
Visiting a file means loading its contents into a buffer (q.v.) where they can be edited. See section Visiting Files.

Whitespace
Whitespace is any run of consecutive formatting characters (space, tab, newline, and backspace).

Widening
Widening is removing any restriction (q.v.) on the current buffer; it is the opposite of narrowing (q.v.). See section Narrowing.

Window
Emacs divides a frame (q.v.) into one or more windows, each of which can display the contents of one buffer (q.v.) at any time. See section The Organization of the Screen, for basic information on how Emacs uses the screen. See section Multiple Windows, for commands to control the use of windows.

Word Abbrev
Synonymous with `abbrev'.

Word Search
Word search is searching for a sequence of words, considering the punctuation between them as insignificant. See section Word Search.

Yanking
Yanking means reinserting text previously killed. It can be used to undo a mistaken kill, or for copying or moving text. Some other systems call this "pasting". See section Yanking.

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