GNU Emacs Manual - Glossary

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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 few letters 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). (Note that many terminals have a key labeled `ALT` which is really a `META` key.) See section Kinds of User Input.
ASCII character
  An ASCII character is either an ASCII control character or an ASCII printing character. See section Kinds of User Input.
ASCII control character
  An ASCII control character is the Control version of an upper-case letter, or the Control version of one of the characters ``@[\]^_?'`.
ASCII printing character
  ASCII printing characters include letters, digits, space, and these punctuation characters: ``!@#$%^& *()_-+=|\~` {}[]:;"' <>,.?/'`.
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 or highlighting 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 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 (q.v.). Most buffers are visiting (q.v.) some file. 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 Kinds of User Input.
`C-M-`
  `C-M-` in the name of a character is an abbreviation for Control-Meta. See section Kinds of User 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.
Character
  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 Kinds of User Input.
Character Set
  Emacs supports a number of character sets, each of which represents a particular alphabet or script. See section International Character Set Support.
Click Event
  A click event is the kind of input event generated when you press a mouse button and release it without moving the mouse. See section Rebinding Mouse Buttons.
Coding System
  A coding system is an encoding for representing text characters in a file or in a stream of information. Emacs has the ability to convert text to or from a variety of coding systems when reading or writing it. See section Coding Systems.
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).
Comment
  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 Compilations under Emacs).
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
  A control character is a character that you type by holding down the `CTRL` key. Some control characters also have their own keys, so that you can type them without using `CTRL`. For example, `RET`, `TAB`, `ESC` and `DEL` are all control characters. See section Kinds of User Input.
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 promote freedom and cooperation, just as copyrights are used by right-wing programmers to gain power over other people. The particular form of copyleft used by the GNU project is called the GNU General Public License. See section GNU GENERAL PUBLIC LICENSE.
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 Rmail 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 File Directories.
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). The messages are stored in the buffer ``*Messages*'` so you can review them later. 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.
Electric
  We say that a character is electric if it is normally self-inserting (q.v.), but the current major mode (q.v.) redefines it to do something else as well. For example, some programming language major modes define particular delimiter characters to reindent the line or insert one or more newlines in addition to self-insertion.
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 Message
  An error message is a single line of output displayed 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), you press the `ESC` key as you would press a letter key, and it applies to the next character you type.
Expunging
  Expunging an Rmail file or Dired buffer is an operation that truly discards the messages or files you have previously flagged for deletion.
File Locking
  Emacs used file locking to notice when two different users start to edit one file at the same time. See section Protection against Simultaneous Editing.
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 shifting text between consecutive lines so that all the lines are approximately the same length. See section Filling Text.
Formatted Text
  Formatted text is text that displays with formatting information while you edit. Formatting information includes fonts, colors, and specified margins. See section Editing Formatted Text.
Frame
  A frame is a rectangular cluster of Emacs windows. Emacs starts out with one frame, but you can create more. You can subdivide each frame into Emacs windows (q.v.). When you are using X windows, all the frames can be visible at the same time. See section Frames and X Windows.
Function Key
  A function key is a key on the keyboard that sends input but 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 Mark Ring
  The global mark ring records the series of buffers you have recently set a mark in. In many cases you can use this to backtrack through buffers you have been editing in, or in which you have found tags. See section The Global Mark Ring.
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.
Highlighting
  Highlighting text means displaying it with a different foreground and/or background color to make it stand out from the rest of the text in the buffer.
Hardcopy
  Hardcopy means printed output. Emacs has commands for making printed listings of text in Emacs buffers. See section Hardcopy Output.
`HELP`
  `HELP` is the Emacs name for `C-h` or `F1`. You can type `HELP` at any time to ask what options you have, or to ask what any command does. 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 Kinds of User Input.
Inbox
  An inbox is a file in which mail is delivered by the operating system. Rmail transfers mail from inboxes to Rmail 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.
Indirect Buffer
  An indirect buffer is a buffer that shares the text of another buffer, called its base buffer. See section Indirect Buffers.
Input Event
  An input event represents, within Emacs, one action taken by the user on the terminal. Input events include typing characters, typing function keys, pressing or releasing mouse buttons, and switching between Emacs frames. See section Kinds of User Input.
Input Method
  An input method is a system for entering non-ASCII text characters by typing sequences of ASCII characters (q.v.). See section Input Methods.
Insertion
  Insertion means copying text into the buffer, either from the keyboard or from some other place in Emacs.
Interlocking
  Interlocking is a feature for warning when you start to alter a file that someone else is already editing. See section Protection against Simultaneous Editing.
Justification
  Justification means adding extra spaces to lines of text to make them come exactly to a specified width. See section Filling Text.
Keyboard Macro
  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 input events (q.v.) that are 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.
Language Environment
  Your choice of language environment specifies defaults for the input method (q.v.) and coding system (q.v.). See section Language Environments. These defaults are relevant if you edit non-ASCII text (see section International Character Set Support).
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 Kinds of User 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 Kinds of User 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 Composition Method
  A mail composition method is a program runnable within Emacs for editing and sending a mail message. Emacs lets you select from several alternative mail composition methods. See section Mail-Composition Methods.
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; in addition, there is a single global mark ring (q.v.). See section The Mark Ring.
Menu Bar
  The menu bar is the line at the top of an Emacs frame. It contains words you can click on with the mouse to bring up menus. The menu bar feature is supported only with X. See section Menu Bars.
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 Kinds of User 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.
MULE
  MULE refers to the Emacs features for editing non-ASCII text using multibyte characters (q.v.). See section International Character Set Support.
Multibyte Character
  A multibyte character is a character that takes up several buffer positions. Emacs uses multibyte characters to represent non-ASCII text, since the number of non-ASCII characters is much more than 256. See section Introduction to International Character Sets.
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
  Control-J characters in the buffer terminate lines of text and are therefore also 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.
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.
Paragraph
  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 Rmail File
  Your primary Rmail file is the file named ``RMAIL'` in your home directory. That's where Rmail stores your incoming mail, unless you specify a different file name. See section Reading Mail with Rmail.
Primary Selection
  The primary selection is one particular X selection (q.v.); it is the selection that most X applications use for transferring text to and from other applications. The Emacs kill commands set the primary selection and the yank command uses the primary selection when appropriate. See section Deletion and Killing.
Prompt
  A prompt is text printed to ask the user for input. Displaying 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 multi-character key sequence is also a kind of prompting (see section The Echo Area).
Quitting
  Quitting means canceling a partially typed command or a running command, using `C-g` (or `C-`BREAK`` on MS-DOS). See section Quitting and Aborting.
Quoting
  Quoting means depriving a character of its usual special significance. The most common kind of quoting in Emacs is 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.
Quoting File Names
  Quoting a file name turns off the special significance of constructs such as ``$'`, ``~'` and ``:'`. See section Quoted File Names.
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.
Rectangle
  A rectangle consists of the text in a given range of columns on a given range of lines. Normally you specify a rectangle by putting point at one corner and putting the mark at the opposite corner. See section Rectangles.
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 that 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 Kinds of User Input.
Rmail File
  An Rmail file is a file containing text in a special format used by Rmail for storing mail. See section Reading Mail with Rmail.
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.
Scroll Bar
  A scroll bar is a tall thin hollow box that appears at the side of a window. You can use mouse commands in the scroll bar to scroll the window. The scroll bar feature is supported only with X. See section Scroll Bars.
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 or the next match for a specified regular expression. 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. See section Libraries of Lisp Code for Emacs.
Secondary Selection
  The secondary selection is one particular X selection; some X applications can use it for transferring text to and from other applications. Emacs has special mouse commands for transferring text using the secondary selection. See section Secondary Selection.
Selecting
  Selecting a buffer means making it the current (q.v.) buffer. See section Using Multiple Buffers.
Selection
  The X window system allows an application program to specify named selections whose values are text. A program can also read the selections that other programs have set up. This is the principal way of transferring text between window applications. Emacs has commands to work with the primary (q.v.) selection and the secondary (q.v.) selection.
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.
Self-Inserting Character
  A character is self-inserting if typing that character inserts that character in the buffer. Ordinary printing and whitespace characters are self-inserting in Emacs, except in certain special major modes.
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 one of the users to investigate. 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, backslash 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 Kinds of User Input.
Tags Table
  A tags table is a file that serves as an index to the function definitions in one or more other files. See section Tags 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):
  - Data consisting of a sequence of characters, as opposed to binary numbers, images, graphics commands, executable programs, and the like. The contents of an Emacs buffer are always text in this sense.
  - Data consisting of written human language, as opposed to programs, or following the stylistic conventions of human language.
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.
User Option
  A user option is a variable (q.v.) that exists so that you can customize Emacs by setting it to a new value. See section Variables.
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 `user 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.
WYSIWYG
  WYSIWYG stands for `What you see is what you get.' Emacs generally provides WYSIWYG editing for files of characters; in Enriched mode (see section Editing Formatted Text), it provides WYSIWYG editing for files that include text formatting information.
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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