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   You are reading about GNU Emacs, the GNU incarnation of the advanced,
self-documenting, customizable, extensible real-time display editor
Emacs.  (The `G' in `GNU' is not silent.)

   We say that Emacs is a "display" editor because normally the text
being edited is visible on the screen and is updated automatically as
you type.  Note: Display.

   We call Emacs a "real-time" editor because the display is updated
very frequently, usually after each character or pair of characters you
type.  This minimizes the amount of information you must keep in your
head as you edit.  Note: Real-time.

   We call Emacs advanced because it provides facilities that go beyond
simple insertion and deletion: filling of text; automatic indentation of
programs; viewing two or more files at once; and dealing in terms of
characters, words, lines, sentences, paragraphs, and pages, as well as
expressions and comments in several different programming languages.
It is much easier to type one command meaning "go to the end of the
paragraph" than to find that spot with simple cursor keys.

   "Self-documenting" means that at any time you can type a special
character, `Control-h', to find out what your options are.  You can
also use `C-h' to find out what a command does, or to find all the
commands relevant to a topic.  Note: Help.

   "Customizable" means you can change the definitions of Emacs
commands.  For example, if you use a programming language in which
comments start with `<**' and end with `**>', you can tell the Emacs
comment manipulation commands to use those strings (Note: Comments.).
Another sort of customization is rearrangement of the command set.
For example, you can set up the four basic cursor motion commands (up,
down, left and right) on keys in a diamond pattern on the keyboard if
you prefer.  Note: Customization.

   "Extensible" means you can go beyond simple customization and write
entirely new commands, programs in the Lisp language to be run by
Emacs's own Lisp interpreter.  Emacs is an "on-line extensible" system:
it is divided into many functions that call each other.  You can
redefine any function in the middle of an editing session and replace
any part of Emacs without making a separate copy of all of Emacs.  Most
of the editing commands of Emacs are written in Lisp; the few
exceptions could have been written in Lisp but are written in C for
efficiency.  Only a programmer can write an extension to Emacs, but
anybody can use it afterward.

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