path: root/doc/emacs/help.texi

@c This is part of the Emacs manual.
@c Copyright (C) 1985--1987, 1993--1995, 1997, 2000--2023 Free Software
@c Foundation, Inc.
@c See file emacs.texi for copying conditions.
@node Help
@chapter Help
@cindex help
@cindex self-documentation
@findex help-command
@kindex C-h
@kindex F1

@kindex C-h C-h
@findex help-for-help
  Emacs provides a wide variety of help commands, all accessible
through the prefix key @kbd{C-h} (or, equivalently, the function key
@key{F1}).  These help commands are described in the following
sections.  You can also type @kbd{C-h C-h} to view a list of help
commands (@code{help-for-help}).  You can scroll the list with
@key{SPC} and @key{DEL}, then type the help command you want.  To
cancel, type @kbd{C-g}.

@cindex help buffer
  Many help commands display their information in a special @dfn{help
buffer}.  In this buffer, you can type @key{SPC} and @key{DEL} to
scroll and type @key{RET} to follow hyperlinks.  @xref{Help Mode}.

@vindex help-window-select
  By default, help commands display the help buffer in a separate
window without selecting that window.  The variable
@code{help-window-select} controls this: its default value is
@code{nil}; if it's customized to the value @code{t}, the help window
is unconditionally selected by help commands, and if its value is
@code{other}, the help window is selected only if there are more than
two windows on the selected frame.

@vindex help-window-keep-selected
  Conversely, many commands in the @samp{*Help*} buffer will pop up a
new window to display the results.  For instance, clicking on the link
to show the source code, or using the @key{i} command to display the
manual entry, will (by default) pop up a new window.  If
@code{help-window-keep-selected} is changed to non-@code{nil}, the
window displaying the @samp{*Help*} buffer will be reused instead.

@cindex searching documentation efficiently
@cindex looking for a subject in documentation
  If you are looking for a certain feature, but don't know what it is
called or where to look, we recommend three methods.  First, try an
apropos command, then try searching the manual index, then look in the
FAQ and the package keywords, and finally try listing external packages.

@table @kbd
@item C-h a @var{topics} @key{RET}
This searches for commands whose names match the argument
@var{topics}.  The argument can be a keyword, a list of keywords, or a
regular expression (@pxref{Regexps}).  @xref{Apropos}.

@item C-h i d m emacs @key{RET} i @var{topic} @key{RET}
This searches for @var{topic} in the indices of the Emacs Info manual,
displaying the first match found.  Press @kbd{,} to see subsequent
matches.  You can use a regular expression as @var{topic}.

@item C-h i d m emacs @key{RET} s @var{topic} @key{RET}
Similar, but searches the @emph{text} of the manual rather than the
indices.

@item C-h C-f
This displays the Emacs FAQ, using Info.

@item C-h p
This displays the available Emacs packages based on keywords.
@xref{Package Keywords}.

@item M-x list-packages
This displays a list of external packages.  @xref{Packages}.
@end table

  @kbd{C-h} or @key{F1} mean ``help'' in various other contexts as
well.  For instance, you can type them after a prefix key to view a
list of the keys that can follow the prefix key.  (You can also use
@kbd{?} in this context.  A few prefix keys don't support @kbd{C-h}
or @kbd{?} in this way, because they define other meanings for those
inputs, but they all support @key{F1}.)

@menu
* Help Summary::        Brief list of all Help commands.
* Key Help::            Asking what a key does in Emacs.
* Name Help::           Asking about a command, variable or function name.
* Apropos::             Asking what pertains to a given topic.
* Help Mode::           Special features of Help mode and Help buffers.
* Package Keywords::    Finding Lisp libraries by keywords (topics).
* Language Help::       Help relating to international language support.
* Misc Help::           Other help commands.
* Help Files::          Commands to display auxiliary help files.
* Help Echo::           Help on active text and tooltips (``balloon help'').
@end menu

@iftex
@node Help Summary
@end iftex
@ifnottex
@node Help Summary
@section Help Summary
@end ifnottex

  Here is a summary of help commands for accessing the built-in
documentation.  Most of these are described in more detail in the
following sections.

@table @kbd
@item C-h a @var{topics} @key{RET}
Display a list of commands whose names match @var{topics}
(@code{apropos-command}).  @xref{Apropos}.
@item C-h b
Display all active key bindings; minor mode bindings first, then those
of the major mode, then global bindings (@code{describe-bindings}).
@xref{Misc Help}.
@item C-h c @var{key}
Show the name of the command that the key sequence @var{key} is bound
to (@code{describe-key-briefly}).  Here @kbd{c} stands for
``character''.  For more extensive information on @var{key}, use
@kbd{C-h k}.  @xref{Key Help}.
@item C-h d @var{topics} @key{RET}
Display the commands and variables whose documentation matches
@var{topics} (@code{apropos-documentation}).  @xref{Apropos}.
@item C-h e
Display the @file{*Messages*} buffer
(@code{view-echo-area-messages}).  @xref{Misc Help}.
@item C-h f @var{function} @key{RET}
Display documentation on the Lisp function named @var{function}
(@code{describe-function}).  Since commands are Lisp functions, this
works for commands too, but you can also use @code{C-h x}.  @xref{Name Help}.
@item C-h h
Display the @file{HELLO} file, which shows examples of various character
sets.
@item C-h i
Run Info, the GNU documentation browser (@code{info}).  The Emacs
manual is available in Info.  @xref{Misc Help}.
@item C-h k @var{key}
Display the name and documentation of the command that @var{key} runs
(@code{describe-key}).  @xref{Key Help}.
@item C-h l
Display a description of your last 300 keystrokes
(@code{view-lossage}).  @xref{Misc Help}.
@item C-h m
Display documentation of the current major mode and minor modes
(@code{describe-mode}).  @xref{Misc Help}.
@item C-h n
Display news of recent Emacs changes (@code{view-emacs-news}).
@xref{Help Files}.
@item C-h o @var{symbol}
Display documentation of the Lisp symbol named @var{symbol}
(@code{describe-symbol}).  This will show the documentation of all
kinds of symbols: functions, variables, and faces.  @xref{Name Help}.
@item C-h p
Find packages by topic keyword (@code{finder-by-keyword}).
@xref{Package Keywords}.  This lists packages using a package menu
buffer.  @xref{Packages}.
@item C-h P @var{package} @key{RET}
Display documentation about the specified package
(@code{describe-package}).  @xref{Package Keywords}.
@item C-h r
Display the Emacs manual in Info (@code{info-emacs-manual}).
@item C-h s
Display the contents of the current @dfn{syntax table}
(@code{describe-syntax}).  @xref{Misc Help}.  The syntax table says
which characters are opening delimiters, which are parts of words, and
so on.  @xref{Syntax Tables,, Syntax Tables, elisp, The Emacs Lisp
Reference Manual}, for details.
@item C-h t
Enter the Emacs interactive tutorial (@code{help-with-tutorial}).
@item C-h v @var{var} @key{RET}
Display the documentation of the Lisp variable @var{var}
(@code{describe-variable}).  @xref{Name Help}.
@item C-h w @var{command} @key{RET}
Show which keys run the command named @var{command} (@code{where-is}).
@xref{Key Help}.
@item C-h x @var{command} @key{RET}
Display documentation on the named @var{command}
(@code{describe-command}).  @xref{Name Help}.
@item C-h C @var{coding} @key{RET}
Describe the coding system @var{coding}
(@code{describe-coding-system}).  @xref{Coding Systems}.
@item C-h C @key{RET}
Describe the coding systems currently in use.
@item C-h F @var{command} @key{RET}
Enter Info and go to the node that documents the Emacs command
@var{command} (@code{Info-goto-emacs-command-node}).  @xref{Name Help}.
@item C-h I @var{method} @key{RET}
Describe the input method @var{method} (@code{describe-input-method}).
@xref{Select Input Method}.
@item C-h K @var{key}
Enter Info and go to the node that documents the key sequence
@var{key} (@code{Info-goto-emacs-key-command-node}).  @xref{Key Help}.
@item C-h L @var{language-env} @key{RET}
Display information on the character sets, coding systems, and input
methods used in language environment @var{language-env}
(@code{describe-language-environment}).  @xref{Language Environments}.
@item C-h S @var{symbol} @key{RET}
Display the Info documentation on symbol @var{symbol} according to the
programming language you are editing (@code{info-lookup-symbol}).
@xref{Misc Help}.
@item C-h .
Display the help message for a special text area, if point is in one
(@code{display-local-help}).  (These include, for example, links in
@file{*Help*} buffers.)  @xref{Help Echo}.  If you invoke
this command with a prefix argument, @kbd{C-u C-h .}, and point is on
a button or a widget, this command will pop a new buffer that
describes that button/widget.
@end table

@node Key Help
@section Documentation for a Key

@findex describe-key-briefly
@findex describe-key
  The help commands to get information about a key sequence are
@kbd{C-h c} (@code{describe-key-briefly}) and @kbd{C-h k}
(@code{describe-key}).

@kindex C-h c
  @kbd{C-h c @var{key}} displays in the echo area the name of the
command that @var{key} is bound to.  For example, @kbd{C-h c C-f}
displays @samp{forward-char}.

@cindex documentation string
@kindex C-h k
  @kbd{C-h k @var{key}} is similar but gives more information: it
displays a help buffer containing the command's @dfn{documentation
string}, which describes exactly what the command does.

@kindex C-h K
@findex Info-goto-emacs-key-command-node
  @kbd{C-h K @var{key}} displays the section of the Emacs manual that
describes the command corresponding to @var{key}.

  @kbd{C-h c}, @kbd{C-h k} and @kbd{C-h K} work for any sort of key
sequences, including function keys, menus, and mouse events (except
that @kbd{C-h c} ignores mouse movement events).  For instance, after
@kbd{C-h k} you can select a menu item from the menu bar, to view the
documentation string of the command it runs.

@kindex C-h w
@findex where-is
  @kbd{C-h w @var{command} @key{RET}} lists the keys that are bound to
@var{command}.  It displays the list in the echo area.  If it says the
command is not on any key, that means you must use @kbd{M-x} to run
it.  @kbd{C-h w} runs the command @code{where-is}.

@findex button-describe
@findex widget-describe
  Some modes in Emacs use various buttons (@pxref{Buttons,,,elisp, The
Emacs Lisp Reference Manual}) and widgets
(@pxref{Introduction,,,widget, Emacs Widgets}) that can be clicked to
perform some action.  To find out what function is ultimately invoked
by these buttons, Emacs provides the @code{button-describe} and
@code{widget-describe} commands, that should be run with point over
the button.

@node Name Help
@section Help by Command or Variable Name

@kindex C-h x
@findex describe-command
  @kbd{C-h x @var{command} @key{RET}} (@code{describe-command})
displays the documentation of the named @var{command}, in a
window.  For example,

@example
C-h x auto-fill-mode @key{RET}
@end example

@noindent
displays the documentation of @code{auto-fill-mode}.  This is how you
would get the documentation of a command that is not bound to any key
(one which you would normally run using @kbd{M-x}).

@kindex C-h f
@findex describe-function
  @kbd{C-h f @var{function} @key{RET}} (@code{describe-function})
displays the documentation of Lisp @var{function}.  This command is
intended for Lisp functions that you use in a Lisp program.  For
example, if you have just written the expression
@code{(make-vector len)} and want to check that you are using
@code{make-vector} properly, type @w{@kbd{C-h f make-vector @key{RET}}}.
Additionally, since all commands are Lisp functions, you can also use
this command to view the documentation of any command.

  If you type @kbd{C-h f @key{RET}}, it describes the function called
by the innermost Lisp expression in the buffer around point,
@emph{provided} that function name is a valid, defined Lisp function.
(That name appears as the default while you enter the argument.)  For
example, if point is located following the text @samp{(make-vector
(car x)}, the innermost list containing point is the one that starts
with @samp{(make-vector}, so @w{@kbd{C-h f @key{RET}}} describes the
function @code{make-vector}.

  @kbd{C-h f} is also useful just to verify that you spelled a
function name correctly.  If the minibuffer prompt for @kbd{C-h f}
shows the function name from the buffer as the default, it means that
name is defined as a Lisp function.  Type @kbd{C-g} to cancel the
@kbd{C-h f} command if you don't really want to view the
documentation.

@vindex help-enable-symbol-autoload
  If you request help for an autoloaded function whose @code{autoload}
form (@pxref{Autoload,,, elisp, The Emacs Lisp Reference Manual})
doesn't provide a doc string, the @file{*Help*} buffer won't have any
doc string to display.  In that case, if
@code{help-enable-symbol-autoload} is non-@code{nil}, Emacs will try
to load the file in which the function is defined to see whether
there's a doc string there.

@findex shortdoc
  You can get an overview of functions relevant for a particular topic
by using the @kbd{M-x shortdoc} command.  This will prompt you for an
area of interest, e.g., @code{string}, and pop you to a buffer where
many of the functions relevant for handling strings are listed.

@kindex C-h v
@findex describe-variable
  @kbd{C-h v} (@code{describe-variable}) is like @kbd{C-h f} but
describes Lisp variables instead of Lisp functions.  Its default is
the Lisp symbol around or before point, if that is the name of a
defined Lisp variable.  @xref{Variables}.

  Help buffers that describe Emacs variables and functions normally
have hyperlinks to the corresponding source code, if you have the
source files installed (@pxref{Hyperlinking}).

@kindex C-h F
@findex Info-goto-emacs-command-node
  To find a command's documentation in a manual, use @kbd{C-h F}
(@code{Info-goto-emacs-command-node}).  This knows about various
manuals, not just the Emacs manual, and finds the right one.

@kindex C-h o
@findex describe-symbol
  @kbd{C-h o} (@code{describe-symbol}) is like @kbd{C-h f} and
@kbd{C-h v}, but it describes any symbol, be it a function, a
variable, or a face.  If the symbol has more than one definition, like
it has both definition as a function and as a variable, this command
will show the documentation of all of them, one after the other.

@vindex completions-detailed
  If the @code{completions-detailed} user option is non-@code{nil},
some commands provide details about the possible values when
displaying completions.  For instance, @kbd{C-h o TAB} will then
include the first line of the doc string, and will also say whether
each symbol is a function or a variable (and so on).  Which details
are included varies depending on the command used.

@node Apropos
@section Apropos
@cindex apropos

  The @dfn{apropos} commands answer questions like, ``What are the
commands for working with files?''  More precisely, you specify your
query as an @dfn{apropos pattern}, which is either a word, a list of
words, or a regular expression.

  Each of the following apropos commands reads an apropos pattern in
the minibuffer, searches for items that match the pattern, and
displays the results in a different window.

@table @kbd
@item C-h a
@kindex C-h a
@findex apropos-command
Search for commands (@code{apropos-command}).  With a prefix argument,
search for noninteractive functions too.

@item M-x apropos
@findex apropos
Search for functions and variables.  Both interactive functions
(commands) and noninteractive functions can be found by this.

@item M-x apropos-user-option
@findex apropos-user-option
Search for user-customizable variables.  With a prefix argument,
search for non-customizable variables too.

@item M-x apropos-variable
@findex apropos-variable
Search for variables.  With a prefix argument, search for
customizable variables only.

@item M-x apropos-local-variable
@findex apropos-local-variable
Search for buffer-local variables.

@item M-x apropos-value
@findex apropos-value
Search for variables whose values match the specified pattern.  With a
prefix argument, search also for functions with definitions matching
the pattern, and Lisp symbols with properties matching the pattern.

@item M-x apropos-local-value
@findex apropos-local-value
Search for buffer-local variables whose values match the specified
pattern.

@item C-h d
@kindex C-h d
@findex apropos-documentation
Search for functions and variables whose documentation strings match
the specified pattern (@code{apropos-documentation}).
@end table

  The simplest kind of apropos pattern is one word.  Anything
containing that word matches the pattern.  Thus, to find commands that
work on files, type @kbd{C-h a file @key{RET}}.  This displays a list
of all command names that contain @samp{file}, including
@code{copy-file}, @code{find-file}, and so on.  Each command name
comes with a brief description and a list of keys you can currently
invoke it with.  In our example, it would say that you can invoke
@code{find-file} by typing @kbd{C-x C-f}.

@vindex help-window-select@r{, and apropos commands}
  By default, the window showing the apropos buffer with the results
of the query is not selected, but you can cause it to be selected by
customizing the variable @code{help-window-select} to any
non-@code{nil} value.

  For more information about a function definition, variable or symbol
property listed in an apropos buffer, you can click on it with
@kbd{mouse-1} or @kbd{mouse-2}, or move there and type @key{RET}.

  When you specify more than one word in the apropos pattern, a name
must contain at least two of the words in order to match.  Thus, if
you are looking for commands to kill a chunk of text before point, you
could try @kbd{C-h a kill back backward behind before @key{RET}}.  The
real command name @code{kill-backward} will match that; if there were
a command @code{kill-text-before}, it would also match, since it
contains two of the specified words.

  For even greater flexibility, you can specify a regular expression
(@pxref{Regexps}).  An apropos pattern is interpreted as a regular
expression if it contains any of the regular expression special
characters, @samp{^$*+?.\[}.

  Following the conventions for naming Emacs commands, here are some
words that you'll find useful in apropos patterns.  By using them in
@kbd{C-h a}, you will also get a feel for the naming conventions.

@quotation
char, line, word, sentence, paragraph, region, page, sexp, list, defun,
rect, buffer, frame, window, face, file, dir, register, mode, beginning, end,
forward, backward, next, previous, up, down, search, goto, kill, delete,
mark, insert, yank, fill, indent, case, change, set, what, list, find,
view, describe, default.
@end quotation

@vindex apropos-do-all
  If the variable @code{apropos-do-all} is non-@code{nil}, most
apropos commands behave as if they had been given a prefix argument.
There is one exception: @code{apropos-variable} without a prefix
argument will always search for all variables, no matter what the
value of @code{apropos-do-all} is.

@vindex apropos-sort-by-scores
@cindex apropos search results, order by score
@vindex apropos-documentation-sort-by-scores
  By default, all apropos commands except @code{apropos-documentation}
list their results in alphabetical order.  If the variable
@code{apropos-sort-by-scores} is non-@code{nil}, these commands
instead try to guess the relevance of each result, and display the
most relevant ones first.  The @code{apropos-documentation} command
lists its results in order of relevance by default; to list them in
alphabetical order, change the variable
@code{apropos-documentation-sort-by-scores} to @code{nil}.

@node Help Mode
@section Help Mode Commands
@findex help-mode
@cindex help mode

  Help buffers have Help mode as their major mode.  Help mode provides
the same commands as View mode (@pxref{View Mode}); for instance,
@key{SPC} scrolls forward, and @key{DEL} or @kbd{S-@key{SPC}} scrolls
backward.  It also provides a few special commands:

@table @kbd
@item @key{RET}
Follow a cross reference at point (@code{help-follow}).
@item @key{TAB}
Move point forward to the next hyperlink (@code{forward-button}).
@item S-@key{TAB}
Move point back to the previous hyperlink (@code{backward-button}).
@item mouse-1
@itemx mouse-2
Follow a hyperlink that you click on.
@item n
@itemx p
Move forward and back between pages in the Help buffer.
@item C-c C-c
Show all documentation about the symbol at point
(@code{help-follow-symbol}).
@item C-c C-f
@itemx r
Go forward in history of help commands (@code{help-go-forward}).
@item C-c C-b
@itemx l
Go back in history of help commands (@code{help-go-back}).
@item s
View the source of the current help topic (if any)
(@code{help-view-source}).
@item i
Look up the current topic in the manual(s) (@code{help-goto-info}).
@item I
Look up the current topic in the Emacs Lisp manual
(@code{help-goto-lispref-info}).
@item c
Customize the variable or the face (@code{help-customize}).
@end table

@cindex hyperlink
@findex help-follow
@findex help-go-back
@findex help-go-forward
@kindex RET @r{(Help mode)}
@kindex C-c C-b @r{(Help mode)}
@kindex l @r{(Help mode)}
@kindex C-c C-f @r{(Help mode)}
@kindex r @r{(Help mode)}
  When a function name, variable name, or face name (@pxref{Faces})
appears in the documentation in the help buffer, it is normally an
underlined @dfn{hyperlink}.  To view the associated documentation,
move point there and type @key{RET} (@code{help-follow}), or click on
the hyperlink with @kbd{mouse-1} or @kbd{mouse-2}.  Doing so replaces
the contents of the help buffer; to retrace your steps, type @kbd{C-c
C-b} or @kbd{l} (@code{help-go-back}).  While retracing your steps,
you can go forward by using @kbd{C-c C-f} or @kbd{r}
(@code{help-go-forward}).

@kindex TAB @r{(Help mode)}
@findex forward-button
@kindex S-TAB @r{(Help mode)}
@findex backward-button
  To move between hyperlinks in a help buffer, use @key{TAB}
(@code{forward-button}) to move forward to the next hyperlink and
@kbd{S-@key{TAB}} (@code{backward-button}) to move back to the
previous hyperlink.  These commands act cyclically; for instance,
typing @key{TAB} at the last hyperlink moves back to the first
hyperlink.

@vindex help-clean-buttons
  By default, many links in the help buffer are displayed surrounded
by quote characters.  If the @code{help-clean-buttons} user option is
non-@code{nil}, these quote characters are removed from the buffer.

@kindex n @r{(Help mode)}
@kindex p @r{(Help mode)}
@findex help-goto-next-page
@findex help-goto-previous-page
  Help buffers produced by some Help commands (like @kbd{C-h b}, which
shows a long list of key bindings) are divided into pages by the
@samp{^L} character.  In such buffers, the @kbd{n}
(@code{help-goto-next-page}) command will take you to the next start
of page, and the @kbd{p} (@code{help-goto-previous-page}) command will
take you to the previous start of page.  This way you can quickly
navigate between the different kinds of documentation in a help
buffer.

@cindex URL, viewing in help
@cindex help, viewing web pages
@cindex viewing web pages in help
@cindex web pages, viewing in help
  A help buffer can also contain hyperlinks to Info manuals, source
code definitions, and URLs (web pages).  The first two are opened in
Emacs, and the third using a web browser via the @code{browse-url}
command (@pxref{Browse-URL}).

  To view all documentation about any symbol in the text, move point
to the symbol and type @kbd{C-c C-c} (@code{help-follow-symbol}).
This shows the documentation for all the meanings of the symbol---as a
variable, as a function, and/or as a face.

@node Package Keywords
@section Keyword Search for Packages
@cindex finder

Most optional features in Emacs are grouped into @dfn{packages}.
Emacs contains several hundred built-in packages, and more can be
installed over the network (@pxref{Packages}).

@kindex C-h p
@findex finder-by-keyword
  To make it easier to find packages related to a topic, most packages
are associated with one or more @dfn{keywords} based on what they do.
Type @kbd{C-h p} (@code{finder-by-keyword}) to bring up a list of
package keywords, together with a description of what the keywords
mean.  To view a list of packages for a given keyword, type @key{RET}
on that line; this displays the list of packages in a Package Menu
buffer (@pxref{Package Menu}).

@findex describe-package
@kindex C-h P
  @kbd{C-h P} (@code{describe-package}) prompts for the name of a
package (@pxref{Packages}), and displays a help buffer describing the
attributes of the package and the features that it implements.  The
buffer lists the keywords that relate to the package in the form of
buttons.  Click on a button with @kbd{mouse-1} or @kbd{mouse-2} to see
the list of other packages related to that keyword.

@node Language Help
@section Help for International Language Support

  For information on a specific language environment (@pxref{Language
Environments}), type @kbd{C-h L}
(@code{describe-language-environment}).  This displays a help buffer
describing the languages supported by the language environment, and
listing the associated character sets, coding systems, and input
methods, as well as some sample text for that language environment.

  The command @kbd{C-h h} (@code{view-hello-file}) displays the file
@file{etc/HELLO}, which demonstrates various character sets by showing
how to say ``hello'' in many languages.

  The command @kbd{C-h I} (@code{describe-input-method}) describes an
input method---either a specified input method, or by default the
input method currently in use.  @xref{Input Methods}.

  The command @kbd{C-h C} (@code{describe-coding-system}) describes
coding systems---either a specified coding system, or the ones
currently in use.  @xref{Coding Systems}.

@node Misc Help
@section Other Help Commands

@kindex C-h i
@kindex C-h 4 i
@findex info
@findex info-other-window
@cindex Info
@cindex manuals, included
  @kbd{C-h i} (@code{info}) runs the Info program, which browses
structured documentation files.  @kbd{C-h 4 i}
(@code{info-other-window}) does the same, but shows the Info buffer in
another window.  The entire Emacs manual is available within Info,
along with many other manuals for the GNU system.  Type @kbd{h} after
entering Info to run a tutorial on using Info.

@cindex find Info manual by its file name
  With a numeric argument @var{n}, @kbd{C-h i} selects the Info buffer
@samp{*info*<@var{n}>}.  This is useful if you want to browse multiple
Info manuals simultaneously.  If you specify just @kbd{C-u} as the
prefix argument, @kbd{C-h i} prompts for the name of a documentation
file, so you can browse a file which doesn't have an entry in the
top-level Info menu.

  The help commands @kbd{C-h F @var{function} @key{RET}} and @kbd{C-h
K @var{key}}, described above, enter Info and go straight to the
documentation of @var{function} or @var{key}.

@kindex C-h S
@findex info-lookup-symbol
  When editing a program, if you have an Info version of the manual
for the programming language, you can use @kbd{C-h S}
(@code{info-lookup-symbol}) to find an entry for a symbol (keyword,
function or variable) in the proper manual.  The details of how this
command works depend on the major mode.

@kindex C-h l
@findex view-lossage
@findex lossage-size
  If something surprising happens, and you are not sure what you typed,
use @kbd{C-h l} (@code{view-lossage}).  @kbd{C-h l} displays your last
input keystrokes and the commands they invoked.  By default, Emacs
stores the last 300 keystrokes; if you wish, you can change this number with
the command @code{lossage-size}.
If you see commands that you are not familiar with, you can use @kbd{C-h k} or
@kbd{C-h f} to find out what they do.

@kindex C-h e
@findex view-echo-area-messages
  To review recent echo area messages, use @kbd{C-h e}
(@code{view-echo-area-messages}).  This displays the buffer
@file{*Messages*}, where those messages are kept.

@kindex C-h m
@findex describe-mode
  Each Emacs major mode typically redefines a few keys and makes other
changes in how editing works.  @kbd{C-h m} (@code{describe-mode})
displays documentation on the current major mode, which normally
describes the commands and features that are changed in this mode, and
also its key bindings.

@kindex C-h b
@findex describe-bindings
@kindex C-h s
@findex describe-syntax
  @kbd{C-h b} (@code{describe-bindings}) and @kbd{C-h s}
(@code{describe-syntax}) show other information about the current
environment within Emacs.  @kbd{C-h b} displays a list of all the key
bindings now in effect: first the local bindings of the current minor
modes, then the local bindings defined by the current major mode, and
finally the global bindings (@pxref{Key Bindings}).  @kbd{C-h s}
displays the contents of the syntax table, with explanations of each
character's syntax (@pxref{Syntax Tables,, Syntax Tables, elisp, The
Emacs Lisp Reference Manual}).

@findex describe-prefix-bindings
  You can get a list of subcommands for a particular prefix key by
typing @kbd{C-h}, @kbd{?}, or @key{F1}
(@code{describe-prefix-bindings}) after the prefix key.  (There are a
few prefix keys for which not all of these keys work---those that
provide their own bindings for that key.  One of these prefix keys
is @key{ESC}, because @kbd{@key{ESC} C-h} and @kbd{@key{ESC} ?} are
actually @kbd{C-M-h} (@code{mark-defun}) and @kbd{M-?}
(@code{xref-find-references}), respectively.  However,
@w{@kbd{@key{ESC} @key{F1}}} works fine.)

@findex describe-keymap
Finally, @kbd{M-x describe-keymap} prompts for the name of a keymap,
with completion, and displays a listing of all key bindings in that
keymap.

@node Help Files
@section Help Files

  Apart from the built-in documentation and manuals, Emacs contains
several other files describing topics like copying conditions, release
notes, instructions for debugging and reporting bugs, and so forth.
You can use the following commands to view these files.  Apart from
@kbd{C-h g}, they all have the form @kbd{C-h C-@var{char}}.

@kindex C-h C-c
@findex describe-copying
@kindex C-h C-d
@findex view-emacs-debugging
@kindex C-h C-e
@findex view-external-packages
@kindex C-h C-f
@findex view-emacs-FAQ
@kindex C-h g
@findex describe-gnu-project
@kindex C-h C-m
@findex view-order-manuals
@kindex C-h C-n
@findex view-emacs-news
@kindex C-h C-o
@findex describe-distribution
@kindex C-h C-p
@findex view-emacs-problems
@kindex C-h C-t
@findex view-emacs-todo
@kindex C-h C-w
@findex describe-no-warranty

@table @kbd
@item C-h C-c
Display the rules under which you can copy and redistribute Emacs
(@code{describe-copying}).
@item C-h C-d
Display help for debugging Emacs (@code{view-emacs-debugging}).
@item C-h C-e
Display information about where to get external packages
(@code{view-external-packages}).
@item C-h C-f
Display the Emacs frequently-answered-questions list (@code{view-emacs-FAQ}).
@item C-h g
Visit the @uref{https://www.gnu.org, page} with information about the GNU
Project (@code{describe-gnu-project}).
@item C-h C-m
Display information about ordering printed copies of Emacs manuals
(@code{view-order-manuals}).
@item C-h C-n
Display the news, which lists the new features in this
version of Emacs (@code{view-emacs-news}).
@item C-h C-o
Display how to order or download the latest version of
Emacs and other GNU software (@code{describe-distribution}).
@item C-h C-p
Display the list of known Emacs problems, sometimes with suggested
workarounds (@code{view-emacs-problems}).
@item C-h C-t
Display the Emacs to-do list (@code{view-emacs-todo}).
@item C-h C-w
Display the full details on the complete absence of warranty for GNU
Emacs (@code{describe-no-warranty}).
@end table

@node Help Echo
@section Help on Active Text and Tooltips

@cindex tooltip help
@cindex balloon help
@cindex active text
  In Emacs, stretches of @dfn{active text} (text that does something
special in response to mouse clicks or @key{RET}) often have
associated help text.  This includes hyperlinks in Emacs buffers, as
well as parts of the mode line.  On graphical displays, as well as
some text terminals which support mouse tracking, moving the mouse
over the active text displays the help text as a @dfn{tooltip}.
@xref{Tooltips}.

@kindex C-h .
@findex display-local-help
@vindex help-at-pt-display-when-idle
  On terminals that don't support mouse-tracking, you can display the
help text for active buffer text at point by typing @kbd{C-h .}
(@code{display-local-help}).  This shows the help text in the echo
area.  To display help text automatically whenever it is available at
point, set the variable @code{help-at-pt-display-when-idle} to
@code{t}.