@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990, 1991, 1992, 1993, 1995, 1998 Free Software Foundation, Inc.
+@c Copyright (C) 1990, 1991, 1992, 1993, 1995, 1998, 1999, 2002, 2003,
+@c 2004, 2005 Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/tips
-@node Tips, GNU Emacs Internals, System Interface, Top
+@node Tips, GNU Emacs Internals, GPL, Top
@appendix Tips and Conventions
@cindex tips
@cindex standards of coding style
previous chapters, and describes conventions Emacs Lisp programmers
should follow.
+ You can automatically check some of the conventions described below by
+running the command @kbd{M-x checkdoc RET} when visiting a Lisp file.
+It cannot check all of the conventions, and not all the warnings it
+gives necessarily correspond to problems, but it is worth examining them
+all.
+
@menu
* Coding Conventions:: Conventions for clean and robust programs.
+* Key Binding Conventions:: Which keys should be bound by which programs.
+* Programming Tips:: Making Emacs code fit smoothly in Emacs.
* Compilation Tips:: Making compiled code run fast.
+* Warning Tips:: Turning off compiler warnings.
* Documentation Tips:: Writing readable documentation strings.
* Comment Tips:: Conventions for writing comments.
* Library Headers:: Standard headers for library packages.
@itemize @bullet
@item
-Since all global variables share the same name space, and all functions
-share another name space, you should choose a short word to distinguish
-your program from other Lisp programs. Then take care to begin the
-names of all global variables, constants, and functions with the chosen
-prefix. This helps avoid name conflicts.
+Simply loading the package should not change Emacs's editing behavior.
+Include a command or commands to enable and disable the feature,
+or to invoke it.
+
+This convention is mandatory for any file that includes custom
+definitions. If fixing such a file to follow this convention requires
+an incompatible change, go ahead and make the incompatible change;
+don't postpone it.
+
+@item
+Since all global variables share the same name space, and all
+functions share another name space, you should choose a short word to
+distinguish your program from other Lisp programs.@footnote{The
+benefits of a Common Lisp-style package system are considered not to
+outweigh the costs.} Then take care to begin the names of all global
+variables, constants, and functions in your program with the chosen
+prefix. This helps avoid name conflicts. (Occasionally, for a command
+name intended for users to use, it is cleaner if some words come
+before the package name prefix.)
This recommendation applies even to names for traditional Lisp
-primitives that are not primitives in Emacs Lisp---even to
+primitives that are not primitives in Emacs Lisp---such as
@code{copy-list}. Believe it or not, there is more than one plausible
way to define @code{copy-list}. Play it safe; append your name prefix
to produce a name like @code{foo-copy-list} or @code{mylib-copy-list}
and send mail to @samp{bug-gnu-emacs@@gnu.org} suggesting we add
it to Emacs. If and when we do, we can change the name easily enough.
-If one prefix is insufficient, your package may use two or three
+If one prefix is insufficient, your package can use two or three
alternative common prefixes, so long as they make sense.
Separate the prefix from the rest of the symbol name with a hyphen,
Lisp programs.
@item
-It is often useful to put a call to @code{provide} in each separate
-library program, at least if there is more than one entry point to the
-program.
+Put a call to @code{provide} at the end of each separate Lisp file.
@item
-If a file requires certain other library programs to be loaded
+If a file requires certain other Lisp programs to be loaded
beforehand, then the comments at the beginning of the file should say
so. Also, use @code{require} to make sure they are loaded.
that could cause name clashes for users who don't use that package.
However, there is no problem with using the @code{cl} package at compile
-time, for the sake of macros. You do that like this:
-
-@example
-(eval-when-compile (require 'cl))
-@end example
+time, with @code{(eval-when-compile (require 'cl))}.
@item
When defining a major mode, please follow the major mode
If a user option variable records a true-or-false condition, give it a
name that ends in @samp{-flag}.
+@item
+If the purpose of a variable is to store a single function, give it a
+name that ends in @samp{-function}. If the purpose of a variable is
+to store a list of functions (i.e., the variable is a hook), please
+follow the naming conventions for hooks. @xref{Hooks}.
+
+@item
+@cindex unloading packages
+If loading the file adds functions to hooks, define a function
+@code{@var{feature}-unload-hook}, where @var{feature} is the name of
+the feature the package provides, and make it undo any such changes.
+Using @code{unload-feature} to unload the file will run this function.
+@xref{Unloading}.
+
+@item
+It is a bad idea to define aliases for the Emacs primitives. Normally
+you should use the standard names instead. The case where an alias
+may be useful is where it facilitates backwards compatibility or
+portability.
+
+@item
+If a package needs to define an alias or a new function for
+compatibility with some other version of Emacs, name it with the package
+prefix, not with the raw name with which it occurs in the other version.
+Here is an example from Gnus, which provides many examples of such
+compatibility issues.
+
+@example
+(defalias 'gnus-point-at-bol
+ (if (fboundp 'point-at-bol)
+ 'point-at-bol
+ 'line-beginning-position))
+@end example
+
+@item
+Redefining (or advising) an Emacs primitive is discouraged. It may do
+the right thing for a particular program, but there is no telling what
+other programs might break as a result.
+
+@item
+If a file does replace any of the functions or library programs of
+standard Emacs, prominent comments at the beginning of the file should
+say which functions are replaced, and how the behavior of the
+replacements differs from that of the originals.
+
+@item
+Avoid using macros that define functions and variables with names that
+are constructed. It is best for maintenance when the name of the
+function or variable being defined is given explicitly in the source
+code, as the second element of the list---as it is when you use
+@code{defun}, @code{defalias}, @code{defvar} and @code{defcustom}.
+
+@item
+Please keep the names of your Emacs Lisp source files to 13 characters
+or less. This way, if the files are compiled, the compiled files' names
+will be 14 characters or less, which is short enough to fit on all kinds
+of Unix systems.
+
+@item
+In some other systems there is a convention of choosing variable names
+that begin and end with @samp{*}. We don't use that convention in Emacs
+Lisp, so please don't use it in your programs. (Emacs uses such names
+only for special-purpose buffers.) The users will find Emacs more
+coherent if all libraries use the same conventions.
+
+@item
+Indent each function with @kbd{C-M-q} (@code{indent-sexp}) using the
+default indentation parameters.
+
+@item
+Don't make a habit of putting close-parentheses on lines by themselves;
+Lisp programmers find this disconcerting. Once in a while, when there
+is a sequence of many consecutive close-parentheses, it may make sense
+to split the sequence in one or two significant places.
+
+@item
+Please put a copyright notice and copying permission notice on the
+file if you distribute copies. Use a notice like this one:
+
+@smallexample
+;; Copyright (C) @var{year} @var{name}
+
+;; This program is free software; you can redistribute it and/or
+;; modify it under the terms of the GNU General Public License as
+;; published by the Free Software Foundation; either version 2 of
+;; the License, or (at your option) any later version.
+
+;; This program is distributed in the hope that it will be
+;; useful, but WITHOUT ANY WARRANTY; without even the implied
+;; warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
+;; PURPOSE. See the GNU General Public License for more details.
+
+;; You should have received a copy of the GNU General Public
+;; License along with this program; if not, write to the Free
+;; Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
+;; MA 02110-1301 USA
+@end smallexample
+
+If you have signed papers to assign the copyright to the Foundation,
+then use @samp{Free Software Foundation, Inc.} as @var{name}.
+Otherwise, use your name. See also @xref{Library Headers}.
+@end itemize
+
+@node Key Binding Conventions
+@section Key Binding Conventions
+
+@itemize @bullet
+@item
+@cindex mouse-2
+@cindex references, following
+Special major modes used for read-only text should usually redefine
+@kbd{mouse-2} and @key{RET} to trace some sort of reference in the text.
+Modes such as Dired, Info, Compilation, and Occur redefine it in this
+way.
+
+In addition, they should mark the text as a kind of ``link'' so that
+@kbd{mouse-1} will follow it also. @xref{Links and Mouse-1}.
+
@item
@cindex reserved keys
@cindex keys, reserved
-Please do not define @kbd{C-c @var{letter}} as a key in your major
-modes. These sequences are reserved for users; they are the
-@strong{only} sequences reserved for users, so do not block them.
+Please do not define @kbd{C-c @var{letter}} as a key in Lisp programs.
+Sequences consisting of @kbd{C-c} and a letter (either upper or lower
+case) are reserved for users; they are the @strong{only} sequences
+reserved for users, so do not block them.
-Instead, define sequences consisting of @kbd{C-c} followed by a control
-character, a digit, or certain punctuation characters. These sequences
-are reserved for major modes.
+Changing all the Emacs major modes to respect this convention was a
+lot of work; abandoning this convention would make that work go to
+waste, and inconvenience users. Please comply with it.
-Changing all the Emacs major modes to follow this convention was a lot
-of work. Abandoning this convention would make that work go to waste,
-and inconvenience users.
+@item
+Function keys @key{F5} through @key{F9} without modifier keys are
+also reserved for users to define.
+
+@item
+Applications should not bind mouse events based on button 1 with the
+shift key held down. These events include @kbd{S-mouse-1},
+@kbd{M-S-mouse-1}, @kbd{C-S-mouse-1}, and so on. They are reserved for
+users.
+
+@item
+Sequences consisting of @kbd{C-c} followed by a control character or a
+digit are reserved for major modes.
@item
Sequences consisting of @kbd{C-c} followed by @kbd{@{}, @kbd{@}},
not absolutely prohibited, but if you do that, the major mode binding
may be shadowed from time to time by minor modes.
-@item
-Function keys @key{F5} through @key{F9} without modifier keys are
-reserved for users to define.
-
@item
Do not bind @kbd{C-h} following any prefix character (including
@kbd{C-c}). If you don't bind @kbd{C-h}, it is automatically available
@item
Anything which acts like a temporary mode or state which the user can
-enter and leave should define @kbd{@key{ESC} @key{ESC}} of
+enter and leave should define @kbd{@key{ESC} @key{ESC}} or
@kbd{@key{ESC} @key{ESC} @key{ESC}} as a way to escape.
For a state which accepts ordinary Emacs commands, or more generally any
after @key{ESC}. In these states, you should define @kbd{@key{ESC}
@key{ESC} @key{ESC}} as the way to escape. Otherwise, define
@kbd{@key{ESC} @key{ESC}} instead.
+@end itemize
-@item
-Applications should not bind mouse events based on button 1 with the
-shift key held down. These events include @kbd{S-mouse-1},
-@kbd{M-S-mouse-1}, @kbd{C-S-mouse-1}, and so on. They are reserved for
-users.
-
-@item
-Special major modes used for read-only text should usually redefine
-@kbd{mouse-2} and @key{RET} to trace some sort of reference in the text.
-Modes such as Dired, Info, Compilation, and Occur redefine it in this
-way.
-
-@item
-When a package provides a modification of ordinary Emacs behavior, it is
-good to include a command to enable and disable the feature, Provide a
-command named @code{@var{whatever}-mode} which turns the feature on or
-off, and make it autoload (@pxref{Autoload}). Design the package so
-that simply loading it has no visible effect---that should not enable
-the feature. Users will request the feature by invoking the command.
-
-@item
-It is a bad idea to define aliases for the Emacs primitives. Use the
-standard names instead.
-
-@item
-Redefining (or advising) an Emacs primitive is discouraged. It may do
-the right thing for a particular program, but there is no telling what
-other programs might break as a result.
-
-@item
-If a file does replace any of the functions or library programs of
-standard Emacs, prominent comments at the beginning of the file should
-say which functions are replaced, and how the behavior of the
-replacements differs from that of the originals.
+@node Programming Tips
+@section Emacs Programming Tips
-@item
-Please keep the names of your Emacs Lisp source files to 13 characters
-or less. This way, if the files are compiled, the compiled files' names
-will be 14 characters or less, which is short enough to fit on all kinds
-of Unix systems.
+ Following these conventions will make your program fit better
+into Emacs when it runs.
+@itemize @bullet
@item
Don't use @code{next-line} or @code{previous-line} in programs; nearly
always, @code{forward-line} is more convenient as well as more
@code{beginning-of-buffer}, @code{end-of-buffer}
@item
@code{replace-string}, @code{replace-regexp}
+@item
+@code{insert-file}, @code{insert-buffer}
@end itemize
-If you just want to move point, or replace a certain string, without any
-of the other features intended for interactive users, you can replace
-these functions with one or two lines of simple Lisp code.
+If you just want to move point, or replace a certain string, or insert
+a file or buffer's contents, without any of the other features
+intended for interactive users, you can replace these functions with
+one or two lines of simple Lisp code.
@item
Use lists rather than vectors, except when there is a particular reason
no need to insert or delete elements (only lists allow that).
@item
-The recommended way to print a message in the echo area is with
+The recommended way to show a message in the echo area is with
the @code{message} function, not @code{princ}. @xref{The Echo Area}.
@item
with a period.
@item
-Many commands that take a long time to execute display a message that
-says @samp{Operating...} when they start, and change it to
-@samp{Operating...done} when they finish. Please keep the style of
-these messages uniform: @emph{no} space around the ellipsis, and
-@emph{no} period at the end.
-
-@item
-Try to avoid using recursive edits. Instead, do what the Rmail @kbd{e}
-command does: use a new local keymap that contains one command defined
-to switch back to the old local keymap. Or do what the
-@code{edit-options} command does: switch to another buffer and let the
-user switch back at will. @xref{Recursive Editing}.
+A question asked in the minibuffer with @code{y-or-n-p} or
+@code{yes-or-no-p} should start with a capital letter and end with
+@samp{? }.
@item
-In some other systems there is a convention of choosing variable names
-that begin and end with @samp{*}. We don't use that convention in Emacs
-Lisp, so please don't use it in your programs. (Emacs uses such names
-only for special-purpose buffers.) The users will find Emacs more
-coherent if all libraries use the same conventions.
+When you mention a default value in a minibuffer prompt,
+put it and the word @samp{default} inside parentheses.
+It should look like this:
-@item
-Try to avoid compiler warnings about undefined free variables, by adding
-@code{defvar} definitions for these variables.
-
-If you bind a variable in one function, and use it or set it in another
-function, the compiler warns about the latter function unless the
-variable has a definition. But often these variables have short names,
-and it is not clean for Lisp packages to define such variable names.
-Therefore, you should rename the variable to start with the name prefix
-used for the other functions and variables in your package.
+@example
+Enter the answer (default 42):
+@end example
@item
-Indent each function with @kbd{C-M-q} (@code{indent-sexp}) using the
-default indentation parameters.
+In @code{interactive}, if you use a Lisp expression to produce a list
+of arguments, don't try to provide the ``correct'' default values for
+region or position arguments. Instead, provide @code{nil} for those
+arguments if they were not specified, and have the function body
+compute the default value when the argument is @code{nil}. For
+instance, write this:
-@item
-Don't make a habit of putting close-parentheses on lines by themselves;
-Lisp programmers find this disconcerting. Once in a while, when there
-is a sequence of many consecutive close-parentheses, it may make sense
-to split the sequence in one or two significant places.
+@example
+(defun foo (pos)
+ (interactive
+ (list (if @var{specified} @var{specified-pos})))
+ (unless pos (setq pos @var{default-pos}))
+ ...)
+@end example
-@item
-Please put a copyright notice on the file if you give copies to anyone.
-Use a message like this one:
+@noindent
+rather than this:
-@smallexample
-;; Copyright (C) @var{year} @var{name}
+@example
+(defun foo (pos)
+ (interactive
+ (list (if @var{specified} @var{specified-pos}
+ @var{default-pos})))
+ ...)
+@end example
-;; This program is free software; you can redistribute it and/or
-;; modify it under the terms of the GNU General Public License as
-;; published by the Free Software Foundation; either version 2 of
-;; the License, or (at your option) any later version.
+@noindent
+This is so that repetition of the command will recompute
+these defaults based on the current circumstances.
-;; This program is distributed in the hope that it will be
-;; useful, but WITHOUT ANY WARRANTY; without even the implied
-;; warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR
-;; PURPOSE. See the GNU General Public License for more details.
+You do not need to take such precautions when you use interactive
+specs @samp{d}, @samp{m} and @samp{r}, because they make special
+arrangements to recompute the argument values on repetition of the
+command.
-;; You should have received a copy of the GNU General Public
-;; License along with this program; if not, write to the Free
-;; Software Foundation, Inc., 59 Temple Place, Suite 330, Boston,
-;; MA 02111-1307 USA
-@end smallexample
+@item
+Many commands that take a long time to execute display a message that
+says something like @samp{Operating...} when they start, and change it to
+@samp{Operating...done} when they finish. Please keep the style of
+these messages uniform: @emph{no} space around the ellipsis, and
+@emph{no} period after @samp{done}.
-If you have signed papers to assign the copyright to the Foundation,
-then use @samp{Free Software Foundation, Inc.} as @var{name}.
-Otherwise, use your name.
+@item
+Try to avoid using recursive edits. Instead, do what the Rmail @kbd{e}
+command does: use a new local keymap that contains one command defined
+to switch back to the old local keymap. Or do what the
+@code{edit-options} command does: switch to another buffer and let the
+user switch back at will. @xref{Recursive Editing}.
@end itemize
@node Compilation Tips
@item
@cindex profiling
@cindex timing programs
-@cindex @file{profile.el}
@cindex @file{elp.el}
-Profile your program with the @file{profile} library or the @file{elp}
-library. See the files @file{profile.el} and @file{elp.el} for
-instructions.
+Profile your program with the @file{elp} library. See the file
+@file{elp.el} for instructions.
+
+@item
+@cindex @file{benchmark.el}
+@cindex benchmarking
+Check the speed of individual Emacs Lisp forms using the
+@file{benchmark} library. See the functions @code{benchmark-run} and
+@code{benchmark-run-compiled} in @file{benchmark.el}.
@item
Use iteration rather than recursion whenever possible.
search functions can be used.
@item
-Certain built-in functions are handled specially in byte-compiled code,
+Certain built-in functions are handled specially in byte-compiled code,
avoiding the need for an ordinary function call. It is a good idea to
use these functions rather than alternatives. To see whether a function
is handled specially by the compiler, examine its @code{byte-compile}
the speed. @xref{Inline Functions}.
@end itemize
+@node Warning Tips
+@section Tips for Avoiding Compiler Warnings
+
+@itemize @bullet
+@item
+Try to avoid compiler warnings about undefined free variables, by adding
+dummy @code{defvar} definitions for these variables, like this:
+
+@example
+(defvar foo)
+@end example
+
+Such a definition has no effect except to tell the compiler
+not to warn about uses of the variable @code{foo} in this file.
+
+@item
+If you use many functions and variables from a certain file, you can
+add a @code{require} for that package to avoid compilation warnings
+for them. For instance,
+
+@example
+(eval-when-compile
+ (require 'foo))
+@end example
+
+@item
+If you bind a variable in one function, and use it or set it in
+another function, the compiler warns about the latter function unless
+the variable has a definition. But adding a definition would be
+unclean if the variable has a short name, since Lisp packages should
+not define short variable names. The right thing to do is to rename
+this variable to start with the name prefix used for the other
+functions and variables in your package.
+
+@item
+The last resort for avoiding a warning, when you want to do something
+that usually is a mistake but it's not a mistake in this one case,
+is to put a call to @code{with-no-warnings} around it.
+@end itemize
+
@node Documentation Tips
@section Tips for Documentation Strings
-@tindex checkdoc-minor-mode
@findex checkdoc-minor-mode
Here are some tips and conventions for the writing of documentation
strings. You can check many of these conventions by running the command
An internal variable or subroutine of a Lisp program might as well have
a documentation string. In earlier Emacs versions, you could save space
by using a comment instead of a documentation string, but that is no
-longer the case.
+longer the case---documentation strings now take up very little space in
+a running Emacs.
+
+@item
+Format the documentation string so that it fits in an Emacs window on an
+80-column screen. It is a good idea for most lines to be no wider than
+60 characters. The first line should not be wider than 67 characters
+or it will look bad in the output of @code{apropos}.
+
+You can fill the text if that looks good. However, rather than blindly
+filling the entire documentation string, you can often make it much more
+readable by choosing certain line breaks with care. Use blank lines
+between topics if the documentation string is long.
@item
The first line of the documentation string should consist of one or two
complete sentences that stand on their own as a summary. @kbd{M-x
-apropos} displays just the first line, and if it doesn't stand on its
-own, the result looks bad. In particular, start the first line with a
-capital letter and end with a period.
+apropos} displays just the first line, and if that line's contents don't
+stand on their own, the result looks bad. In particular, start the
+first line with a capital letter and end with a period.
+
+For a function, the first line should briefly answer the question,
+``What does this function do?'' For a variable, the first line should
+briefly answer the question, ``What does this value mean?''
+
+Don't limit the documentation string to one line; use as many lines as
+you need to explain the details of how to use the function or
+variable. Please use complete sentences for the rest of the text too.
-The documentation string can have additional lines that expand on the
-details of how to use the function or variable. The additional lines
-should be made up of complete sentences also, but they may be filled if
-that looks good.
+@item
+The first line should mention all the important arguments of the
+function, and should mention them in the order that they are written
+in a function call. If the function has many arguments, then it is
+not feasible to mention them all in the first line; in that case, the
+first line should mention the first few arguments, including the most
+important arguments.
@item
-For consistency, phrase the verb in the first sentence of a
-function's documentation string as an infinitive with ``to'' omitted. For
-instance, use ``Return the cons of A and B.'' in preference to ``Returns
-the cons of A and B@.'' Usually it looks good to do likewise for the
-rest of the first paragraph. Subsequent paragraphs usually look better
-if they have proper subjects.
+For consistency, phrase the verb in the first sentence of a function's
+documentation string as an imperative---for instance, use ``Return the
+cons of A and B.'' in preference to ``Returns the cons of A and B@.''
+Usually it looks good to do likewise for the rest of the first
+paragraph. Subsequent paragraphs usually look better if each sentence
+is indicative and has a proper subject.
@item
Write documentation strings in the active voice, not the passive, and in
``Display text in boldface.''
@item
-Do not start or end a documentation string with whitespace.
+When a command is meaningful only in a certain mode or situation,
+do mention that in the documentation string. For example,
+the documentation of @code{dired-find-file} is:
+
+@example
+In Dired, visit the file or directory named on this line.
+@end example
@item
-Format the documentation string so that it fits in an Emacs window on an
-80-column screen. It is a good idea for most lines to be no wider than
-60 characters. The first line can be wider if necessary to fit the
-information that ought to be there.
+Do not start or end a documentation string with whitespace.
-However, rather than simply filling the entire documentation string, you
-can make it much more readable by choosing line breaks with care.
-Use blank lines between topics if the documentation string is long.
-
@item
@strong{Do not} indent subsequent lines of a documentation string so
that the text is lined up in the source code with the text of the first
all non-@code{nil} values are equivalent and indicate explicitly what
@code{nil} and non-@code{nil} mean.
+@item
+The documentation string for a function that is a yes-or-no predicate
+should start with words such as ``Return t if @dots{}'', to indicate
+explicitly what constitutes ``truth''. The word ``return'' avoids
+starting the sentence with lower-case ``t'', which is somewhat
+distracting.
+
@item
When a function's documentation string mentions the value of an argument
of the function, use the argument name in capital letters as if it were
a name for that value. Thus, the documentation string of the function
-@code{/} refers to its second argument as @samp{DIVISOR}, because the
-actual argument name is @code{divisor}.
+@code{eval} refers to its second argument as @samp{FORM}, because the
+actual argument name is @code{form}:
+
+@example
+Evaluate FORM and return its value.
+@end example
-Also use all caps for meta-syntactic variables, such as when you show
-the decomposition of a list or vector into subunits, some of which may
-vary.
+Also write metasyntactic variables in capital letters, such as when you
+show the decomposition of a list or vector into subunits, some of which
+may vary. @samp{KEY} and @samp{VALUE} in the following example
+illustrate this practice:
+
+@example
+The argument TABLE should be an alist whose elements
+have the form (KEY . VALUE). Here, KEY is ...
+@end example
+@item
+Never change the case of a Lisp symbol when you mention it in a doc
+string. If the symbol's name is @code{foo}, write ``foo'', not
+``Foo'' (which is a different symbol).
+
+This might appear to contradict the policy of writing function
+argument values, but there is no real contradiction; the argument
+@emph{value} is not the same thing as the @emph{symbol} which the
+function uses to hold the value.
+
+If this puts a lower-case letter at the beginning of a sentence
+and that annoys you, rewrite the sentence so that the symbol
+is not at the start of it.
+
+@item
+If a line in a documentation string begins with an open-parenthesis,
+write a backslash before the open-parenthesis, like this:
+
+@example
+The argument FOO can be either a number
+\(a buffer position) or a string (a file name).
+@end example
+
+This prevents the open-parenthesis from being treated as the start of a
+defun (@pxref{Defuns,, Defuns, emacs, The GNU Emacs Manual}).
+
+@anchor{Docstring hyperlinks}
@item
@iftex
When a documentation string refers to a Lisp symbol, write it as it
around it. For example: @samp{`lambda'}. There are two exceptions:
write @code{t} and @code{nil} without single-quotes.
@end iftex
-@ifinfo
+@ifnottex
When a documentation string refers to a Lisp symbol, write it as it
would be printed (which usually means in lower case), with single-quotes
around it. For example: @samp{lambda}. There are two exceptions: write
t and nil without single-quotes. (In this manual, we use a different
convention, with single-quotes for all symbols.)
-@end ifinfo
+@end ifnottex
Help mode automatically creates a hyperlink when a documentation string
uses a symbol name inside single quotes, if the symbol has either a
does not make a hyperlink to the documentation, irrelevant here, of the
function @code{list}.
+Normally, no hyperlink is made for a variable without variable
+documentation. You can force a hyperlink for such variables by
+preceding them with one of the words @samp{variable} or
+@samp{option}.
+
+Hyperlinks for faces are only made if the face name is preceded or
+followed by the word @samp{face}. In that case, only the face
+documentation will be shown, even if the symbol is also defined as a
+variable or as a function.
+
+To make a hyperlink to Info documentation, write the name of the Info
+node (or anchor) in single quotes, preceded by @samp{info node},
+@samp{Info node}, @samp{info anchor} or @samp{Info anchor}. The Info
+file name defaults to @samp{emacs}. For example,
+
+@smallexample
+See Info node `Font Lock' and Info node `(elisp)Font Lock Basics'.
+@end smallexample
+
+Finally, to create a hyperlink to URLs, write the URL in single
+quotes, preceded by @samp{URL}. For example,
+
+@smallexample
+The home page for the GNU project has more information (see URL
+`http://www.gnu.org/').
+@end smallexample
+
@item
Don't write key sequences directly in documentation strings. Instead,
use the @samp{\\[@dots{}]} construct to stand for them. For example,
@end group
@end smallexample
-Every function that has no documentation string (presumably one that is
-used only internally within the package it belongs to), should have
-instead a two-semicolon comment right before the function, explaining
-what the function does and how to call it properly. Explain precisely
-what each argument means and how the function interprets its possible
-values.
-
-@item ;;;
-Comments that start with three semicolons, @samp{;;;}, should start at
-the left margin. Such comments are used outside function definitions to
-make general statements explaining the design principles of the program.
-For example:
+We also normally use two semicolons for comments outside functions.
@smallexample
@group
-;;; This Lisp code is run in Emacs
-;;; when it is to operate as a server
-;;; for other processes.
+;; This Lisp code is run in Emacs
+;; when it is to operate as a server
+;; for other processes.
@end group
@end smallexample
+Every function that has no documentation string (presumably one that is
+used only internally within the package it belongs to), should instead
+have a two-semicolon comment right before the function, explaining what
+the function does and how to call it properly. Explain precisely what
+each argument means and how the function interprets its possible values.
+
+@item ;;;
+Comments that start with three semicolons, @samp{;;;}, should start at
+the left margin. These are used, occasionally, for comments within
+functions that should start at the margin. We also use them sometimes
+for comments that are between functions---whether to use two or three
+semicolons depends on whether the comment should be considered a
+``heading'' by Outline minor mode. By default, comments starting with
+at least three semicolons (followed by a single space and a
+non-whitespace character) are considered headings, comments starting
+with two or less are not.
+
Another use for triple-semicolon comments is for commenting out lines
-within a function. We use triple-semicolons for this precisely so that
-they remain at the left margin.
+within a function. We use three semicolons for this precisely so that
+they remain at the left margin. By default, Outline minor mode does
+not consider a comment to be a heading (even if it starts with at
+least three semicolons) if the semicolons are followed by at least two
+spaces. Thus, if you add an introductory comment to the commented out
+code, make sure to indent it by at least two spaces after the three
+semicolons.
@smallexample
(defun foo (a)
-;;; This is no longer necessary.
+;;; This is no longer necessary.
;;; (force-mode-line-update)
(message "Finished with %s" a))
@end smallexample
+When commenting out entire functions, use two semicolons.
+
@item ;;;;
Comments that start with four semicolons, @samp{;;;;}, should be aligned
to the left margin and are used for headings of major sections of a
Emacs has conventions for using special comments in Lisp libraries
to divide them into sections and give information such as who wrote
-them. This section explains these conventions. First, an example:
+them. This section explains these conventions.
+
+ We'll start with an example, a package that is included in the Emacs
+distribution.
+
+ Parts of this example reflect its status as part of Emacs; for
+example, the copyright notice lists the Free Software Foundation as the
+copyright holder, and the copying permission says the file is part of
+Emacs. When you write a package and post it, the copyright holder would
+be you (unless your employer claims to own it instead), and you should
+get the suggested copying permission from the end of the GNU General
+Public License itself. Don't say your file is part of Emacs
+if we haven't installed it in Emacs yet!
+
+ With that warning out of the way, on to the example:
@smallexample
@group
;; This file is part of GNU Emacs.
@dots{}
-;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
-;; Boston, MA 02111-1307, USA.
+;; Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
+;; Boston, MA 02110-1301, USA.
@end group
@end smallexample
@end example
@noindent
-The description should be complete in one line.
+The description should be complete in one line. If the file
+needs a @samp{-*-} specification, put it after @var{description}.
After the copyright notice come several @dfn{header comment} lines,
each beginning with @samp{;; @var{header-name}:}. Here is a table of
names---they have no standard meanings, so they can't do any harm.
We use additional stylized comments to subdivide the contents of the
-library file. Here is a table of them:
+library file. These should be separated by blank lines from anything
+else. Here is a table of them:
@table @samp
@item ;;; Commentary:
text is used by the Finder package, so it should make sense in that
context.
-@item ;;; Documentation
-This has been used in some files in place of @samp{;;; Commentary:},
-but @samp{;;; Commentary:} is preferred.
+@item ;;; Documentation:
+This was used in some files in place of @samp{;;; Commentary:},
+but it is deprecated.
@item ;;; Change Log:
This begins change log information stored in the library file (if you
-store the change history there). For most of the Lisp
-files distributed with Emacs, the change history is kept in the file
-@file{ChangeLog} and not in the source file at all; these files do
-not have a @samp{;;; Change Log:} line.
+store the change history there). For Lisp files distributed with Emacs,
+the change history is kept in the file @file{ChangeLog} and not in the
+source file at all; these files generally do not have a @samp{;;; Change
+Log:} line. @samp{History} is an alternative to @samp{Change Log}.
@item ;;; Code:
This begins the actual code of the program.
Its purpose is to enable people to detect truncated versions of the file
from the lack of a footer line.
@end table
+
+@ignore
+ arch-tag: 9ea911c2-6b1d-47dd-88b7-0a94e8b27c2e
+@end ignore
HCoop / bpt / emacs.git / blobdiff