@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
@c Copyright (C) 1990, 1991, 1992, 1993, 1995, 1998, 1999
-@c Free Software Foundation, Inc.
+@c Free Software Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@setfilename ../info/tips
@node Tips, GNU Emacs Internals, GPL, Top
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 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.
+modes. 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
+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{@}},
that simply loading it has no visible effect---that should not enable
the feature.@footnote{Consider that the package may be loaded
arbitrarily by Custom for instance.} Users will request the feature by
-invoking the command.
+invoking the command. It is a good idea to define this command
+as a minor mode.
+
+@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. Use the
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
@item
Try to avoid compiler warnings about undefined free variables, by adding
-@code{defvar} definitions for these variables.
+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.
-Sometimes adding a @code{require} for another package is useful to avoid
-compilation warnings for variables and functions defined in that
-package. If you do this, often it is better if the @code{require} acts
-only at compile time. Here's how to do that:
+@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. It is better if the @code{require} acts only at compile
+time. Here's how to do this:
@example
(eval-when-compile
- (require 'foo)
- (defvar bar-baz))
+ (require 'foo))
@end example
-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.
+@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
Indent each function with @kbd{C-M-q} (@code{indent-sexp}) using the
@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
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}
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
stand on their own, the result looks bad. In particular, start the
first line with a capital letter and end with a period.
-The documentation string is not limited 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 in the additional lines.
+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.
+
+@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 imperative--for instance, use ``Return the
+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
-has a proper subject.
+is indicative and has a proper subject.
@item
Write documentation strings in the active voice, not the passive, and in
@item
Do not start or end a documentation string with whitespace.
-@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
@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
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
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 in single quotes, preceded by @samp{info node} or @samp{Info
-node}. The Info file name defaults to @samp{emacs}. For example,
+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'.
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 there is a matter of style.
+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 three semicolons for this precisely so that
-they remain at the left margin.
+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
@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
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
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