# glossary.texi   [plain text]

@c This is part of the Emacs manual.
@c Copyright (C) 1985, 1986, 1987, 1993, 1994, 1995, 1997, 2001, 2002,
@c   2003, 2004, 2005, 2006, 2007 Free Software Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Glossary, Key Index, Intro, Top
@unnumbered Glossary

@table @asis
@item 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.
@xref{Abbrevs}.

@item Aborting
Aborting means getting out of a recursive edit (q.v.@:).  The
commands @kbd{C-]} and @kbd{M-x top-level} are used for this.
@xref{Quitting}.

@item 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 @key{ALT}
(usually written @kbd{A-} for short).  (Note that many terminals have a
key labeled @key{ALT} which is really a @key{META} key.)  @xref{User
Input, Alt}.

@item Argument
See numeric argument.'

@item @acronym{ASCII} character
An @acronym{ASCII} character is either an @acronym{ASCII} control character or an @acronym{ASCII}
printing character.  @xref{User Input}.

@item @acronym{ASCII} control character
An @acronym{ASCII} control character is the Control version of an upper-case
letter, or the Control version of one of the characters @samp{@@[\]^_?}.

@item @acronym{ASCII} printing character
@acronym{ASCII} printing characters include letters, digits, space, and these
punctuation characters: @samp{!@@#%^& *()_-+=|\~ @{@}[]:;"' <>,.?/}. @item Auto Fill Mode Auto Fill mode is a minor mode in which text that you insert is automatically broken into lines of a given maximum width. @xref{Filling}. @item 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. @xref{Auto Save}. @item Autoloading Emacs automatically loads Lisp libraries when a Lisp program requests a function or a variable from those libraries. This is called autoloading'. @xref{Lisp Libraries}. @item Backtrace A backtrace is a trace of a series of function calls showing how a program arrived to a certain point. It is used mainly for finding and correcting bugs (q.v.@:). Emacs can display a backtrace when it signals an error or when you type @kbd{C-g} (see quitting'). @xref{Checklist}. @item 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. @xref{Backup}. @item Balancing Parentheses Emacs can balance parentheses (or other matching delimiters) either manually or automatically. You do manual balancing with the commands to move over parenthetical groupings (@pxref{Moving by Parens}). Automatic balancing works by blinking or highlighting the delimiter that matches the one you just inserted (@pxref{Matching,,Matching Parens}). @item Balanced Expressions A balanced expression is a syntactically recognizable expression, such as a symbol, number, string constant, block, or parenthesized expression in C. @xref{Expressions,Balanced Expressions}. @item Balloon Help See tooltips.' @item Base Buffer A base buffer is a buffer whose text is shared by an indirect buffer (q.v.@:). @item Bind To bind a key sequence means to give it a binding (q.v.@:). @xref{Rebinding}. @item 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. @xref{Commands,Binding}. Customization often involves rebinding a character to a different command function. The bindings of all key sequences are recorded in the keymaps (q.v.@:). @xref{Keymaps}. @item Blank Lines Blank lines are lines that contain only whitespace. Emacs has several commands for operating on the blank lines in the buffer. @item Bookmark Bookmarks are akin to registers (q.v.@:) in that they record positions in buffers to which you can return later. Unlike registers, bookmarks persist between Emacs sessions. @item Border A border is a thin space along the edge of the frame, used just for spacing, not for displaying anything. An Emacs frame has an ordinary external border, outside of everything including the menu bar, plus an internal border that surrounds the text windows and their scroll bars and separates them from the menu bar and tool bar. You can customize both borders with options and resources (@pxref{Borders X}). Borders are not the same as fringes (q.v.@:). @item 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 current buffer,' though several can be visible when you are using multiple windows (q.v.@:). Most buffers are visiting (q.v.@:) some file. @xref{Buffers}. @item 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. @xref{Buffers}. @item Bug A bug is an incorrect or unreasonable behavior of a program, or inaccurate or confusing documentation. Emacs developers treat bug reports, both in Emacs code and its documentation, very seriously and ask you to report any bugs you find. @xref{Bugs}. @item Button Down Event A button down event is the kind of input event generated right away when you press down on a mouse button. @xref{Mouse Buttons}. @item By Default See default.' @item Byte Compilation See compilation.' @item @kbd{C-} @kbd{C-} in the name of a character is an abbreviation for Control. @xref{User Input,C-}. @item @kbd{C-M-} @kbd{C-M-} in the name of a character is an abbreviation for Control-Meta. @xref{User Input,C-M-}. @item Case Conversion Case conversion means changing text from upper case to lower case or vice versa. @xref{Case}, for the commands for case conversion. @item Character Characters form the contents of an Emacs buffer; see @ref{Text Characters}. Also, key sequences (q.v.@:) are usually made up of characters (though they may include other input events as well). @xref{User Input}. @item Character Set Emacs supports a number of character sets, each of which represents a particular alphabet or script. @xref{International}. @item Character Terminal See text-only terminal.' @item 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. @xref{Mouse Buttons}. @item Clipboard A clipboard is a buffer provided by the window system for transferring text between applications. On the X Window system, the clipboard is provided in addition to the primary selection (q.v.@:); on MS-Windows and Mac, the clipboard is used @emph{instead} of the primary selection. @xref{Clipboard}. @item 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. @xref{Coding Systems}. @item 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. @xref{Commands}. @item Command History See minibuffer history.' @item Command Name A command name is the name of a Lisp symbol which is a command (@pxref{Commands}). You can invoke any command by its name using @kbd{M-x} (@pxref{M-x,M-x,Running Commands by Name}). @item 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. @xref{Comments}. @item Common Lisp Common Lisp is a dialect of Lisp (q.v.@:) much larger and more powerful than Emacs Lisp. Emacs provides a subset of Common Lisp in the CL package. @xref{Top, Common Lisp, Overview, cl, Common Lisp Extensions}. @item Compilation Compilation is the process of creating an executable program from source code. Emacs has commands for compiling files of Emacs Lisp code (@pxref{Byte Compilation,,, elisp, the Emacs Lisp Reference Manual}) and programs in C and other languages (@pxref{Compilation}). @item Complete Key A complete key is a key sequence which fully specifies one action to be performed by Emacs. For example, @kbd{X} and @kbd{C-f} and @kbd{C-x m} are complete keys. Complete keys derive their meanings from being bound (q.v.@:) to commands (q.v.@:). Thus, @kbd{X} is conventionally bound to a command to insert @samp{X} in the buffer; @kbd{C-x m} is conventionally bound to a command to begin composing a mail message. @xref{Keys}. @item 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 @key{TAB}, @key{SPC} or @key{RET} is typed. @xref{Completion}.@refill @item 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. @xref{Continuation Lines}. A related Emacs feature is filling' (q.v.@:). @item Control Character A control character is a character that you type by holding down the @key{CTRL} key. Some control characters also have their own keys, so that you can type them without using @key{CTRL}. For example, @key{RET}, @key{TAB}, @key{ESC} and @key{DEL} are all control characters. @xref{User Input}. @item Copyleft A copyleft is a notice giving the public legal permission to redistribute and modify a program or other work of art, but requiring modified versions to carry similar permission. Copyright is normally used to keep users divided and helpless; with copyleft we turn that around to empower users and encourage them to cooperate. The particular form of copyleft used by the GNU project is called the GNU General Public License. @xref{Copying}. @item @key{CTRL} The @key{CTRL} or control'' key is what you hold down in order to enter a control character (q.v.). @item 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. @xref{Buffers}. @item Current Line The current line is the line that point is on (@pxref{Point}). @item Current Paragraph The current paragraph is the paragraph that point is in. If point is between two paragraphs, the current paragraph is the one that follows point. @xref{Paragraphs}. @item Current Defun The current defun is the defun (q.v.@:) that point is in. If point is between defuns, the current defun is the one that follows point. @xref{Defuns}. @item 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.' @xref{Point,Cursor}. @item Customization Customization is making minor changes in the way Emacs works. It is often done by setting variables (@pxref{Variables}) or faces (@pxref{Face Customization}), or by rebinding key sequences (@pxref{Keymaps}). @cindex cut and paste @item Cut and Paste See killing' and yanking.' @item 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 @key{RET}. @xref{Minibuffer}. @item Default A default is the value that is used for a certain purpose if and when you do not specify a value to use. @item Default Directory When you specify a file name that does not start with @samp{/} or @samp{~}, it is interpreted relative to the current buffer's default directory. (On MS-Windows and MS-DOS, file names which start with a drive letter @samp{@var{x}:} are treated as absolute, not relative.) @xref{Minibuffer File,Default Directory}. @item Defun A defun is a major definition at the top level in a program. The name defun' comes from Lisp, where most such definitions use the construct @code{defun}. @xref{Defuns}. @item @key{DEL} @key{DEL} is a character that runs the command to delete one character of text before the cursor. It is typically either the @key{DELETE} key or the @key{BACKSPACE} key, whichever one is easy to type. @xref{Erasing,DEL}. @item Deletion Deletion means erasing text without copying it into the kill ring (q.v.@:). The alternative is killing (q.v.@:). @xref{Killing,Deletion}. @item Deletion of Files Deleting a file means erasing it from the file system. @xref{Misc File Ops,Misc File Ops,Miscellaneous File Operations}. @item 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. @xref{Rmail Deletion}. @item 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. @xref{Windows}. @item Directory File directories are named collections in the file system, within which you can place individual files or subdirectories. @xref{Directories}. @item 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. @xref{Dired}. @item 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. @xref{Disabling}. @item Down Event Short for button down event' (q.v.@:). @item 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. @xref{Mouse Buttons}. @item Dribble File A dribble file is a file into which Emacs writes all the characters that you type 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. @xref{Bugs}. @item Echo Area The echo area is the bottom line of the screen, used for echoing the arguments to commands, for asking questions, and showing brief messages (including error messages). The messages are stored in the buffer @samp{*Messages*} so you can review them later. @xref{Echo Area}. @item Echoing Echoing is acknowledging the receipt of input events 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. @item 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. @item End Of Line End of line is a character or a sequence of characters that indicate the end of a text line. On GNU and Unix systems, this is a newline (q.v.@:), but other systems have other conventions. @xref{Coding Systems,end-of-line}. Emacs can recognize several end-of-line conventions in files and convert between them. @item Environment Variable An environment variable is one of a collection of variables stored by the operating system, each one having a name and a value. Emacs can access environment variables set by its parent shell, and it can set variables in the environment it passes to programs it invokes. @xref{Environment}. @item EOL See end of line.' @item 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 displaying an error message (q.v.@:). Type-ahead is discarded. Then Emacs is ready to read another editing command. @item 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. @item @key{ESC} @key{ESC} is a character used as a prefix for typing Meta characters on keyboards lacking a @key{META} key. Unlike the @key{META} key (which, like the @key{SHIFT} key, is held down while another character is typed), you press the @key{ESC} key as you would press a letter key, and it applies to the next character you type. @item Expression See balanced expression.' @item Expunging Expunging an Rmail file or Dired buffer or a Gnus newsgroup buffer is an operation that truly discards the messages or files you have previously flagged for deletion. @item Face A face is a style of displaying characters. It specifies attributes such as font family and size, foreground and background colors, underline and strike-through, background stipple, etc. Emacs provides features to associate specific faces with portions of buffer text, in order to display that text as specified by the face attributes. @xref{Faces}. @item File Locking Emacs uses file locking to notice when two different users start to edit one file at the same time. @xref{Interlocking}. @item 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 @samp{~/} or @samp{~@var{user}/} (a home directory). On MS-Windows/MS-DOS, an absolute file name can also start with a drive letter and a colon @samp{@var{d}:}. 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.@:). @item 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, @file{foo/bar} is a file name containing two components, @samp{foo} and @samp{bar}; it refers to the file named @samp{bar} in the directory named @samp{foo} in the current directory. MS-DOS/MS-Windows file names can also use backslashes to separate components, as in @file{foo\bar}. @item 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. @xref{Filling}. @item Filling Filling text means shifting text between consecutive lines so that all the lines are approximately the same length. @xref{Filling}. Some other editors call this feature line wrapping.' @item Font Lock Font Lock is a mode that highlights parts of buffer text according to its syntax. @xref{Font Lock}. @item Fontset A fontset is a named collection of fonts. A fontset specification lists character sets and which font to use to display each of them. Fontsets make it easy to change several fonts at once by specifying the name of a fontset, rather than changing each font separately. @xref{Fontsets}. @item Formatted Text Formatted text is text that displays with formatting information while you edit. Formatting information includes fonts, colors, and specified margins. @xref{Formatted Text}. @item Formfeed Character See page.' @item 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 a window system (q.v.@:), all the frames can be visible at the same time. @xref{Frames}. Some other editors use the term window'' for this, but in Emacs a window means something else. @item Fringe On a graphical display (q.v.@:), there's a narrow portion of the frame (q.v.@:) between the text area and the window's border. Emacs displays the fringe using a special face (q.v.@:) called @code{fringe}. @xref{Faces,fringe}. @item FTP FTP is an acronym for File Transfer Protocol. Emacs uses an FTP client program to provide access to remote files (q.v.@:). @item Function Key A function key is a key on the keyboard that sends input but does not correspond to any character. @xref{Function Keys}. @item 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. @item 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. @xref{Abbrevs}. @item 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.@:). @xref{Keymaps}. @item Global Mark Ring The global mark ring records the series of buffers you have recently set a mark (q.v.@:) 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 tags table'). @xref{Global Mark Ring}. @item Global Substitution Global substitution means replacing each occurrence of one string by another string throughout a large amount of text. @xref{Replace}. @item 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. @xref{Variables}. @item 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 @key{RET} or @key{ESC}. In Emacs, typing a graphic character inserts that character (in ordinary editing modes). @xref{Inserting Text}. @item Graphical Display A graphical display is one that can display images and multiple fonts. Usually it also has a window system (q.v.@:). @item 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. Emacs uses highlighting in several ways. When you mark a region with the mouse, the region is always highlighted. Optionally Emacs can also highlight the region whenever it is active (@pxref{Transient Mark}). Incremental search also highlights matches (@pxref{Incremental Search}). See also font lock'. @item Hardcopy Hardcopy means printed output. Emacs has commands for making printed listings of text in Emacs buffers. @xref{Printing}. @item @key{HELP} @key{HELP} is the Emacs name for @kbd{C-h} or @key{F1}. You can type @key{HELP} at any time to ask what options you have, or to ask what any command does. @xref{Help}. @item Help Echo Help echo is a short message displayed in the echo area when the mouse pointer is located on portions of display that require some explanations. Emacs displays help echo for menu items, parts of the mode line, tool-bar buttons, etc. On graphics displays, the messages can be displayed as tooltips (q.v.@:). @xref{Tooltips}. @item Hook A hook is a list of functions to be called on specific occasions, such as saving a buffer in a file, major mode activation, etc. By customizing the various hooks, you can modify Emacs's behavior without changing any of its code. @xref{Hooks}. @item 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 @key{HYPER} key. Such characters are given names that start with @kbd{Hyper-} (usually written @kbd{H-} for short). @xref{User Input, Hyper}. @item Iff Iff'' means if and only if.'' This terminology comes from mathematics. @item 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. @xref{Rmail Inbox}. @item Incremental Search Emacs provides an incremental search facility, whereby Emacs searches for the string as you type it. @xref{Incremental Search}. @item 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. @xref{Indentation}. @item Indirect Buffer An indirect buffer is a buffer that shares the text of another buffer, called its base buffer (q.v.@:). @xref{Indirect Buffers}. @item Info Info is the hypertext format used by the GNU project for writing documentation. @item 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. @xref{User Input}. @item Input Method An input method is a system for entering non-@acronym{ASCII} text characters by typing sequences of @acronym{ASCII} characters (q.v.@:). @xref{Input Methods}. @item Insertion Insertion means copying text into the buffer, either from the keyboard or from some other place in Emacs. @item Interlocking Interlocking is a feature for warning when you start to alter a file that someone else is already editing. @xref{Interlocking,Interlocking,Simultaneous Editing}. @item Isearch See incremental search.' @item Justification Justification means adding extra spaces within lines of text to make them extend exactly to a specified width. @xref{Format Justification}. @item Keybinding See binding.' @item 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. @xref{Keyboard Macros}. @cindex keyboard shortcuts @item Keyboard Shortcut A keyboard shortcut is a key sequence (q.v.@:) which invokes a command. What some programs call assigning a keyboard shortcut,'' Emacs calls binding a key sequence.'' See binding.' @item 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.@:). @xref{Keys}. @item 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 @kbd{C-n} to the command function @code{next-line}. @xref{Keymaps}. @item 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. @item 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.@:). @xref{Yanking}. @item 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 that erase text perform killing, as opposed to deletion (q.v.@:). @xref{Killing}. @item Killing a Job 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. @xref{Exiting}. @item Language Environment Your choice of language environment specifies defaults for the input method (q.v.@:) and coding system (q.v.@:). @xref{Language Environments}. These defaults are relevant if you edit non-@acronym{ASCII} text (@pxref{International}). @item Line Wrapping See filling.' @item Lisp Lisp is a programming language. Most of Emacs is written in a dialect of Lisp, called Emacs Lisp, that is extended with special features which make it especially suitable for text editing tasks. @item 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. @xref{Moving by Parens}. @item 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. @item 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. @xref{Abbrevs}. @item 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. @xref{Keymaps}. @item Local Variable A local value of a variable (q.v.@:) applies to only one buffer. @xref{Locals}. @item @kbd{M-} @kbd{M-} in the name of a character is an abbreviation for @key{META}, one of the modifier keys that can accompany any character. @xref{User Input,M-}. @item @kbd{M-C-} @kbd{M-C-} in the name of a character is an abbreviation for Control-Meta; it means the same thing as @kbd{C-M-}. If your terminal lacks a real @key{META} key, you type a Control-Meta character by typing @key{ESC} and then typing the corresponding Control character. @xref{User Input,C-M-}. @item @kbd{M-x} @kbd{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. @xref{M-x,M-x,Running Commands by Name}. @item 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. @xref{Sending Mail}. @xref{Rmail}, for how to read mail. @item 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. @xref{Mail Methods}. @item 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. @xref{Major Modes}. @item Margin The space between the usable part of a window (including the fringe) and the window edge. @item 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. @xref{Mark}. @item 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.@:). @xref{Mark Ring}. @item 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, or you can use a keyboard interface to navigate it. @xref{Menu Bars}. @item Message See mail.' @item Meta Meta is the name of a modifier bit which you can use in a command character. To enter a meta character, you hold down the @key{META} key while typing the character. We refer to such characters with names that start with @kbd{Meta-} (usually written @kbd{M-} for short). For example, @kbd{M-<} is typed by holding down @key{META} and at the same time typing @kbd{<} (which itself is done, on most terminals, by holding down @key{SHIFT} and typing @kbd{,}). @xref{User Input,Meta}. On some terminals, the @key{META} key is actually labeled @key{ALT} or @key{EDIT}. @item Meta Character A Meta character is one whose character code includes the Meta bit. @item Minibuffer The minibuffer is the window that appears when necessary inside the echo area (q.v.@:), used for reading arguments to commands. @xref{Minibuffer}. @item 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. @xref{Minibuffer History}. @item 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. @xref{Minor Modes}. @item Minor Mode Keymap A minor mode keymap is 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. @xref{Keymaps}. @item 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. @xref{Mode Line}. @item 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). @xref{Saving}. @item Moving Text Moving text means erasing it from one place and inserting it in another. The usual way to move text is by killing (q.v.@:) it and then yanking (q.v.@:) it. @xref{Killing}. @item MULE MULE refers to the Emacs features for editing multilingual non-@acronym{ASCII} text using multibyte characters (q.v.@:). @xref{International}. @item Multibyte Character A multibyte character is a character that takes up several bytes in a buffer. Emacs uses multibyte characters to represent non-@acronym{ASCII} text, since the number of non-@acronym{ASCII} characters is much more than 256. @xref{International Chars, International Characters}. @item 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. @xref{Registers}. @item 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 for editing until the boundaries are widened again, but it is still there, and saving the file saves it all. @xref{Narrowing}. @item Newline Control-J characters in the buffer terminate lines of text and are therefore also called newlines. @xref{Text Characters,Newline}. @cindex nil @cindex t @item @code{nil} @code{nil} is a value usually interpreted as a logical false.'' Its opposite is @code{t}, interpreted as true.'' @item 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. @xref{Arguments}. @item 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. @xref{Minor Modes}. @item Page A page is a unit of text, delimited by formfeed characters (@acronym{ASCII} control-L, code 014) coming at the beginning of a line. Some Emacs commands are provided for moving over and operating on pages. @xref{Pages}. @item Paragraph Paragraphs are the medium-size unit of human-language text. There are special Emacs commands for moving over and operating on paragraphs. @xref{Paragraphs}. @item 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. @xref{Syntax}. @item 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. @xref{Point}. @item Prefix Argument See numeric argument.' @item Prefix Key A prefix key is a key sequence (q.v.@:) whose sole function is to introduce a set of longer key sequences. @kbd{C-x} is an example of prefix key; any two-character sequence starting with @kbd{C-x} is therefore a legitimate key sequence. @xref{Keys}. @item Primary Rmail File Your primary Rmail file is the file named @samp{RMAIL} in your home directory. That's where Rmail stores your incoming mail, unless you specify a different file name. @xref{Rmail}. @item 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. @xref{Killing}. @item Prompt A prompt is text used 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 (@pxref{Minibuffer}); the echoing which happens when you pause in the middle of typing a multi-character key sequence is also a kind of prompting (@pxref{Echo Area}). @item Query-Replace Query-replace is an interactive string replacement feature provided by Emacs. @xref{Query Replace}. @item Quitting Quitting means canceling a partially typed command or a running command, using @kbd{C-g} (or @kbd{C-@key{BREAK}} on MS-DOS). @xref{Quitting}. @item Quoting Quoting means depriving a character of its usual special significance. The most common kind of quoting in Emacs is with @kbd{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 @key{DEL}, for example), and quoting it makes it insert itself as if it were not special. Not all contexts allow quoting. @xref{Inserting Text,Quoting}. @item Quoting File Names Quoting a file name turns off the special significance of constructs such as @samp{}, @samp{~} and @samp{:}.  @xref{Quoted File Names}.

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.
@xref{Buffers}.

@item 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 diagonally opposite corner.
@xref{Rectangles}.

@item Recursive Editing Level
A recursive editing level is a state in which part of the execution of
a command involves asking you 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
(@samp{[} and @samp{]}).  @xref{Recursive Edit}.

@item 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.
@xref{Screen,Redisplay}.

@item Regexp
See regular expression.'

@item Region
The region is the text between point (q.v.@:) and the mark (q.v.@:).
Many commands operate on the text of the region.  @xref{Mark,Region}.

@item Register
Registers are named slots in which text or buffer positions or
rectangles can be saved for later use.  @xref{Registers}.  A related
Emacs feature is bookmarks' (q.v.@:).

@item Regular Expression
A regular expression is a pattern that can match various text strings;
for example, @samp{a[0-9]+} matches @samp{a} followed by one or more
digits.  @xref{Regexps}.

@item Remote File
A remote file is a file that is stored on a system other than your own.
Emacs can access files on other computers provided that they are
connected to the same network as your machine, and (obviously) that
@xref{Remote Files}.

@item Repeat Count
See numeric argument.'

@item Replacement
See global substitution.'

@item 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.@:); removing
a restriction is called widening (q.v.@:).  @xref{Narrowing}.

@item @key{RET}
@key{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.@:).  @xref{User Input,Return}.

@item Reverting
Reverting means returning to the original state.  Emacs lets you
revert a buffer by re-reading its file from disk.  @xref{Reverting}.

@item Rmail File
An Rmail file is a file containing text in a special format used by
Rmail for storing mail.  @xref{Rmail}.

@item 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.  @xref{Saving}.

@item 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 under windowing
systems.  @xref{Scroll Bars}.

@item Scrolling
Scrolling means shifting the text in the Emacs window so as to see a
different part of the buffer.  @xref{Scrolling}.

@item Searching
Searching means moving point to the next occurrence of a specified
string or the next match for a specified regular expression.
@xref{Search}.

@item 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 @code{load-path}
holds a search path for finding Lisp library files.  @xref{Lisp Libraries}.

@item 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.  @xref{Secondary Selection}.

@item Selected Frame
The selected frame is the one your input currently operates on.
@xref{Frames}.

@item Selected Window
The selected frame is the one your input currently operates on.
@xref{Basic Window}.

@item Selecting a Buffer
Selecting a buffer means making it the current (q.v.@:) buffer.
@xref{Select Buffer}.

@item Selection
Windowing systems allow an application program to specify
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, and also with the clipboard (q.v.@:).

@item 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,
@kbd{C-h}.  @xref{Help}.

@item 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.

@item Sentences
Emacs has commands for moving by or killing by sentences.
@xref{Sentences}.

@item Sexp
A sexp (short for s-expression'') is the basic syntactic unit of
Lisp in its textual form: either a list, or Lisp atom.  Sexps are also
the balanced expressions (q.v.@:) of the Lisp language; this is why
the commands for editing balanced expressions have sexp' in their
name.  @xref{Expressions,Sexps}.

@item 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
or her work.  Emacs detects all cases of simultaneous editing, and
warns one of the users to investigate.
@xref{Interlocking,Interlocking,Simultaneous Editing}.

@item @key{SPC}
@key{SPC} is the space character, which you enter by pressing the
space bar.

@item Speedbar
The speedbar is a special tall frame that provides fast access to Emacs
buffers, functions within those buffers, Info nodes, and other
interesting parts of text within Emacs.  @xref{Speedbar}.

@item Spell Checking
Spell checking means checking correctness of the written form of each
one of the words in a text.  Emacs uses the Ispell spelling-checker
program to check the spelling of parts of a buffer via a convenient user
interface.  @xref{Spelling}.

@item 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 @samp{"} before and another @samp{"} after.  A @samp{"}
that is part of the string must be written as @samp{\"} and a @samp{\}
that is part of the string must be written as @samp{\\}.  All other
characters, including newline, can be included just by writing them
inside the string; however, backslash sequences as in C, such as
@samp{\n} for newline or @samp{\241} using an octal character code, are
allowed as well.

@item String Substitution
See global substitution'.

@item Syntax Highlighting
See font lock.'

@item Syntax Table
The syntax table tells Emacs which characters are part of a word,
which characters balance each other like parentheses, etc.
@xref{Syntax}.

@item 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
@kbd{Super-} (usually written @kbd{s-} for short).  @xref{User Input,
Super}.

@item Suspending
Suspending Emacs means stopping it temporarily and returning control
to its parent process, which is usually a shell.  Unlike killing a job
(q.v.@:), you can later resume the suspended Emacs job without losing
your buffers, unsaved edits, undo history, etc.  @xref{Exiting}.

@item @key{TAB}
@key{TAB} is the tab character.  In Emacs it is typically used for
indentation or completion.

@item Tags Table
A tags table is a file that serves as an index to the function
definitions in one or more other files.  @xref{Tags}.

@item 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.
@xref{Bugs}.

@item Text
Text' has two meanings (@pxref{Text}):

@itemize @bullet
@item
Data consisting of a sequence of characters, as opposed to binary
numbers, executable programs, and the like.  The basic contents of an
Emacs buffer (aside from the text properties, q.v.@:) are always text
in this sense.
@item
Data consisting of written human language, as opposed to programs,
or following the stylistic conventions of human language.
@end itemize

@item Text-only Terminal
A text-only terminal is a display that is limited to displaying text in
character units.  Such a terminal cannot control individual pixels it
displays.  Emacs supports a subset of display features on text-only
terminals.

@item Text Properties
Text properties are annotations recorded for particular characters in
the buffer.  Images in the buffer are recorded as text properties;
they also specify formatting information.  @xref{Editing Format Info}.

@item Tool Bar
The tool bar is a line (sometimes multiple lines) of icons at the top
of an Emacs frame.  Clicking on one of these icons executes a command.
You can think of this as a graphical relative of the menu bar (q.v.@:).
@xref{Tool Bars}.

@item Tooltips
Tooltips are small windows displaying a help echo (q.v.@:) text that
explains parts of the display, lists useful options available via mouse
clicks, etc.  @xref{Tooltips}.

@item 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
level by aborting (q.v.@:) and quitting (q.v.@:).  @xref{Quitting}.

@item 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, balanced expressions (q.v.@:) or lines
(@pxref{Transpose}).

@item 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
@xref{Continuation Lines,Truncation}.

@item TTY
See text-only terminal.'

@item Undoing
Undoing means making your previous editing go in reverse, bringing
back the text that existed earlier in the editing session.
@xref{Undo}.

@item User Option
A user option is a face (q.v.@:) or a variable (q.v.@:) that exists so
that you can customize Emacs by setting it to a new value.
@xref{Easy Customization}.

@item 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 (@pxref{Variable Index}).  @xref{Variables}, for
information on variables.

@item 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.@:).
@xref{Version Control}.

@item Visiting
where they can be edited.  @xref{Visiting}.

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

@item Widening
Widening is removing any restriction (q.v.@:) on the current buffer;
it is the opposite of narrowing (q.v.@:).  @xref{Narrowing}.

@item 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.
@xref{Screen}, for basic information on how Emacs uses the screen.
@xref{Windows}, for commands to control the use of windows.  Some
other editors use the term window'' for what we call a frame'
(q.v.@:) in Emacs.

@item Window System
A window system is software that operates on a graphical display
(q.v.@:), to subdivide the screen so that multiple applications can
have their] own windows at the same time.  All modern operating systems
include a window system.

@item Word Abbrev
See abbrev.'

@item Word Search
Word search is searching for a sequence of words, considering the
punctuation between them as insignificant.  @xref{Word Search}.

@item WYSIWYG
WYSIWYG stands for What you see is what you get.''  Emacs generally
provides WYSIWYG editing for files of characters; in Enriched mode
(@pxref{Formatted Text}), it provides WYSIWYG editing for files that
include text formatting information.

@item 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.''  @xref{Yanking}.
@end table

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