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1 Quitting and Aborting

C-<Break> (MS-DOS only)

Quit: cancel running or partially typed command.


Abort innermost recursive editing level and cancel the command which invoked it (abort-recursive-edit).


Either quit or abort, whichever makes sense (keyboard-escape-quit).

M-x top-level

Abort all recursive editing levels that are currently executing.

C-x u

Cancel a previously made change in the buffer contents (undo).

There are two ways of canceling a command before it has finished: quitting with C-g, and aborting with C-] or M-x top-level. Quitting cancels a partially typed command, or one which is still running. Aborting exits a recursive editing level and cancels the command that invoked the recursive edit (@pxref{Recursive Edit}).

Quitting with C-g is the way to get rid of a partially typed command, or a numeric argument that you don’t want. Furthermore, if you are in the middle of a command that is running, C-g stops the command in a relatively safe way. For example, if you quit out of a kill command that is taking a long time, either your text will all still be in the buffer, or it will all be in the kill ring, or maybe both. If the region is active, C-g deactivates the mark, unless Transient Mark mode is off (@pxref{Disabled Transient Mark}). If you are in the middle of an incremental search, C-g behaves specially; it may take two successive C-g characters to get out of a search. @xref{Incremental Search}, for details.

On MS-DOS, the character C-<Break> serves as a quit character like C-g. The reason is that it is not feasible, on MS-DOS, to recognize C-g while a command is running, between interactions with the user. By contrast, it is feasible to recognize C-<Break> at all times. @xref{MS-DOS Keyboard}.

C-g works by setting the variable quit-flag to t the instant C-g is typed; Emacs Lisp checks this variable frequently, and quits if it is non-nil. C-g is only actually executed as a command if you type it while Emacs is waiting for input. In that case, the command it runs is keyboard-quit.

On a text terminal, if you quit with C-g a second time before the first C-g is recognized, you activate the emergency-escape feature and return to the shell. See section Emergency Escape.

There are some situations where you cannot quit. When Emacs is waiting for the operating system to do something, quitting is impossible unless special pains are taken for the particular system call within Emacs where the waiting occurs. We have done this for the system calls that users are likely to want to quit from, but it’s possible you will encounter a case not handled. In one very common case—waiting for file input or output using NFS—Emacs itself knows how to quit, but many NFS implementations simply do not allow user programs to stop waiting for NFS when the NFS server is hung.

Aborting with C-] (abort-recursive-edit) is used to get out of a recursive editing level and cancel the command which invoked it. Quitting with C-g does not do this, and could not do this, because it is used to cancel a partially typed command within the recursive editing level. Both operations are useful. For example, if you are in a recursive edit and type C-u 8 to enter a numeric argument, you can cancel that argument with C-g and remain in the recursive edit.

The sequence <ESC> <ESC> <ESC> (keyboard-escape-quit) can either quit or abort. (We defined it this way because <ESC> means “get out” in many PC programs.) It can cancel a prefix argument, clear a selected region, or get out of a Query Replace, like C-g. It can get out of the minibuffer or a recursive edit, like C-]. It can also get out of splitting the frame into multiple windows, as with C-x 1. One thing it cannot do, however, is stop a command that is running. That’s because it executes as an ordinary command, and Emacs doesn’t notice it until it is ready for the next command.

The command M-x top-level is equivalent to enough C-] commands to get you out of all the levels of recursive edits that you are in; it also exits the minibuffer if it is active. C-] gets you out one level at a time, but M-x top-level goes out all levels at once. Both C-] and M-x top-level are like all other commands, and unlike C-g, in that they take effect only when Emacs is ready for a command. C-] is an ordinary key and has its meaning only because of its binding in the keymap. @xref{Recursive Edit}.

C-/ (undo) is not strictly speaking a way of canceling a command, but you can think of it as canceling a command that already finished executing. @xref{Undo}, for more information about the undo facility.

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2 Dealing with Emacs Trouble

This section describes how to recognize and deal with situations in which Emacs does not work as you expect, such as keyboard code mixups, garbled displays, running out of memory, and crashes and hangs.

See section Reporting Bugs, for what to do when you think you have found a bug in Emacs.

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2.1 If <DEL> Fails to Delete

Every keyboard has a large key, usually labeled <BACKSPACE>, which is ordinarily used to erase the last character that you typed. In Emacs, this key is supposed to be equivalent to <DEL>.

When Emacs starts up on a graphical display, it determines automatically which key should be <DEL>. In some unusual cases, Emacs gets the wrong information from the system, and <BACKSPACE> ends up deleting forwards instead of backwards.

Some keyboards also have a <Delete> key, which is ordinarily used to delete forwards. If this key deletes backward in Emacs, that too suggests Emacs got the wrong information—but in the opposite sense.

On a text terminal, if you find that <BACKSPACE> prompts for a Help command, like Control-h, instead of deleting a character, it means that key is actually sending the ‘BS’ character. Emacs ought to be treating <BS> as <DEL>, but it isn’t.

In all of those cases, the immediate remedy is the same: use the command M-x normal-erase-is-backspace-mode. This toggles between the two modes that Emacs supports for handling <DEL>, so if Emacs starts in the wrong mode, this should switch to the right mode. On a text terminal, if you want to ask for help when <BS> is treated as <DEL>, use <F1> instead of C-h; C-? may also work, if it sends character code 127.

To fix the problem in every Emacs session, put one of the following lines into your initialization file (@pxref{Init File}). For the first case above, where <BACKSPACE> deletes forwards instead of backwards, use this line to make <BACKSPACE> act as <DEL>:

(normal-erase-is-backspace-mode 0)

For the other two cases, use this line:

(normal-erase-is-backspace-mode 1)

Another way to fix the problem for every Emacs session is to customize the variable normal-erase-is-backspace: the value t specifies the mode where <BS> or <BACKSPACE> is <DEL>, and nil specifies the other mode. @xref{Easy Customization}.

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2.2 Recursive Editing Levels

Recursive editing levels are important and useful features of Emacs, but they can seem like malfunctions if you do not understand them.

If the mode line has square brackets ‘[…]’ around the parentheses that contain the names of the major and minor modes, you have entered a recursive editing level. If you did not do this on purpose, or if you don’t understand what that means, you should just get out of the recursive editing level. To do so, type M-x top-level. @xref{Recursive Edit}.

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2.3 Garbage on the Screen

If the text on a text terminal looks wrong, the first thing to do is see whether it is wrong in the buffer. Type C-l (recenter-top-bottom) to redisplay the entire screen. If the screen appears correct after this, the problem was entirely in the previous screen update. (Otherwise, see the following section.)

Display updating problems often result from an incorrect terminfo entry for the terminal you are using. The file ‘etc/TERMS’ in the Emacs distribution gives the fixes for known problems of this sort. ‘INSTALL’ contains general advice for these problems in one of its sections. If you seem to be using the right terminfo entry, it is possible that there is a bug in the terminfo entry, or a bug in Emacs that appears for certain terminal types.

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2.4 Garbage in the Text

If C-l shows that the text is wrong, first type C-h l (view-lossage) to see what commands you typed to produce the observed results. Then try undoing the changes step by step using C-x u (undo), until it gets back to a state you consider correct.

If a large portion of text appears to be missing at the beginning or end of the buffer, check for the word ‘Narrow’ in the mode line. If it appears, the text you don’t see is probably still present, but temporarily off-limits. To make it accessible again, type C-x n w (widen). @xref{Narrowing}.

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2.5 Running out of Memory

If you get the error message ‘Virtual memory exceeded’, save your modified buffers with C-x s (save-some-buffers). This method of saving them has the smallest need for additional memory. Emacs keeps a reserve of memory which it makes available when this error happens; that should be enough to enable C-x s to complete its work. When the reserve has been used, ‘!MEM FULL!’ appears at the beginning of the mode line, indicating there is no more reserve.

Once you have saved your modified buffers, you can exit this Emacs session and start another, or you can use M-x kill-some-buffers to free space in the current Emacs job. If this frees up sufficient space, Emacs will refill its memory reserve, and ‘!MEM FULL!’ will disappear from the mode line. That means you can safely go on editing in the same Emacs session.

Do not use M-x buffer-menu to save or kill buffers when you run out of memory, because the Buffer Menu needs a fair amount of memory itself, and the reserve supply may not be enough.

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2.6 When Emacs Crashes

Emacs is not supposed to crash, but if it does, it produces a crash report prior to exiting. The crash report is printed to the standard error stream. If Emacs was started from a graphical desktop on a GNU or Unix system, the standard error stream is commonly redirected to a file such as ‘~/.xsession-errors’, so you can look for the crash report there. On MS-Windows, the crash report is written to a file named ‘emacs_backtrace.txt’ in the current directory of the Emacs process, in addition to the standard error stream.

The format of the crash report depends on the platform. On some platforms, such as those using the GNU C Library, the crash report includes a backtrace describing the execution state prior to crashing, which can be used to help debug the crash. Here is an example for a GNU system:

Fatal error 11: Segmentation fault

The number ‘11’ is the system signal number corresponding to the crash—in this case a segmentation fault. The hexadecimal numbers are program addresses, which can be associated with source code lines using a debugging tool. For example, the GDB command ‘list *0x509af6’ prints the source-code lines corresponding to the ‘emacs[0x509af6]’ entry. If your system has the addr2line utility, the following shell command outputs a backtrace with source-code line numbers:

sed -n 's/.*\[\(.*\)]$/\1/p' backtrace |
  addr2line -C -f -i -p -e bindir/emacs-binary

Here, backtrace is the name of a text file containing a copy of the backtrace, bindir is the name of the directory that contains the Emacs executable, and emacs-binary is the name of the Emacs executable file, normally ‘emacs’ on GNU and Unix systems and ‘emacs.exe’ on MS-Windows and MS-DOS. Omit the ‘-p’ option if your version of addr2line is too old to have it.

Optionally, Emacs can generate a core dump when it crashes, on systems that support core files. A core dump is a file containing voluminous data about the state of the program prior to the crash, usually examined by loading it into a debugger such as GDB. On many platforms, core dumps are disabled by default, and you must explicitly enable them by running the shell command ‘ulimit -c unlimited’ (e.g., in your shell startup script).

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2.7 Recovery After a Crash

If Emacs or the computer crashes, you can recover the files you were editing at the time of the crash from their auto-save files. To do this, start Emacs again and type the command M-x recover-session.

This command initially displays a buffer which lists interrupted session files, each with its date. You must choose which session to recover from. Typically the one you want is the most recent one. Move point to the one you choose, and type C-c C-c.

Then recover-session considers each of the files that you were editing during that session; for each such file, it asks whether to recover that file. If you answer y for a file, it shows the dates of that file and its auto-save file, then asks once again whether to recover that file. For the second question, you must confirm with yes. If you do, Emacs visits the file but gets the text from the auto-save file.

When recover-session is done, the files you’ve chosen to recover are present in Emacs buffers. You should then save them. Only this—saving them—updates the files themselves.

As a last resort, if you had buffers with content which were not associated with any files, or if the autosave was not recent enough to have recorded important changes, you can use the ‘etc/emacs-buffer.gdb’ script with GDB (the GNU Debugger) to retrieve them from a core dump–provided that a core dump was saved, and that the Emacs executable was not stripped of its debugging symbols.

As soon as you get the core dump, rename it to another name such as ‘core.emacs’, so that another crash won’t overwrite it.

To use this script, run gdb with the file name of your Emacs executable and the file name of the core dump, e.g., ‘gdb /usr/bin/emacs core.emacs’. At the (gdb) prompt, load the recovery script: ‘source /usr/src/emacs/etc/emacs-buffer.gdb’. Then type the command ybuffer-list to see which buffers are available. For each buffer, it lists a buffer number. To save a buffer, use ysave-buffer; you specify the buffer number, and the file name to write that buffer into. You should use a file name which does not already exist; if the file does exist, the script does not make a backup of its old contents.

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2.8 Emergency Escape

On text terminals, the emergency escape feature suspends Emacs immediately if you type C-g a second time before Emacs can actually respond to the first one by quitting. This is so you can always get out of GNU Emacs no matter how badly it might be hung. When things are working properly, Emacs recognizes and handles the first C-g so fast that the second one won’t trigger emergency escape. However, if some problem prevents Emacs from handling the first C-g properly, then the second one will get you back to the shell.

When you resume Emacs after a suspension caused by emergency escape, it reports the resumption and asks a question or two before going back to what it had been doing:

Emacs is resuming after an emergency escape.
Auto-save? (y or n)
Abort (and dump core)? (y or n)

Answer each question with y or n followed by <RET>.

Saying y to ‘Auto-save?’ causes immediate auto-saving of all modified buffers in which auto-saving is enabled. Saying n skips this. This question is omitted if Emacs is in a state where auto-saving cannot be done safely.

Saying y to ‘Abort (and dump core)?’ causes Emacs to crash, dumping core. This is to enable a wizard to figure out why Emacs was failing to quit in the first place. Execution does not continue after a core dump.

If you answer this question n, Emacs execution resumes. With luck, Emacs will ultimately do the requested quit. If not, each subsequent C-g invokes emergency escape again.

If Emacs is not really hung, just slow, you may invoke the double C-g feature without really meaning to. Then just resume and answer n to both questions, and you will get back to the former state. The quit you requested will happen by and by.

Emergency escape is active only for text terminals. On graphical displays, you can use the mouse to kill Emacs or switch to another program.

On MS-DOS, you must type C-<Break> (twice) to cause emergency escape—but there are cases where it won’t work, when a system call hangs or when Emacs is stuck in a tight loop in C code.

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3 Reporting Bugs

If you think you have found a bug in Emacs, please report it. We cannot promise to fix it, or always to agree that it is a bug, but we certainly want to hear about it. The same applies for new features you would like to see added. The following sections will help you to construct an effective bug report.

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3.1 Reading Existing Bug Reports and Known Problems

Before reporting a bug, if at all possible please check to see if it is already known about. Indeed, it may already have been fixed in a later release of Emacs, or in the development version. Here is a list of the main places you can read about known issues:

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3.2 When Is There a Bug

If Emacs accesses an invalid memory location (a.k.a. “segmentation fault”) or exits with an operating system error message that indicates a problem in the program (as opposed to something like “disk full”), then it is certainly a bug.

If the Emacs display does not correspond properly to the contents of the buffer, then it is a bug. But you should check that features like buffer narrowing (@pxref{Narrowing}), which can hide parts of the buffer or change how it is displayed, are not responsible.

Taking forever to complete a command can be a bug, but you must make sure that it is really Emacs’s fault. Some commands simply take a long time. Type C-g (C-<Break> on MS-DOS) and then C-h l to see whether the input Emacs received was what you intended to type; if the input was such that you know it should have been processed quickly, report a bug. If you don’t know whether the command should take a long time, find out by looking in the manual or by asking for assistance.

If a command you are familiar with causes an Emacs error message in a case where its usual definition ought to be reasonable, it is probably a bug.

If a command does the wrong thing, that is a bug. But be sure you know for certain what it ought to have done. If you aren’t familiar with the command, it might actually be working right. If in doubt, read the command’s documentation (@pxref{Name Help}).

A command’s intended definition may not be the best possible definition for editing with. This is a very important sort of problem, but it is also a matter of judgment. Also, it is easy to come to such a conclusion out of ignorance of some of the existing features. It is probably best not to complain about such a problem until you have checked the documentation in the usual ways, feel confident that you understand it, and know for certain that what you want is not available. Ask other Emacs users, too. If you are not sure what the command is supposed to do after a careful reading of the manual, check the index and glossary for any terms that may be unclear.

If after careful rereading of the manual you still do not understand what the command should do, that indicates a bug in the manual, which you should report. The manual’s job is to make everything clear to people who are not Emacs experts—including you. It is just as important to report documentation bugs as program bugs.

If the built-in documentation for a function or variable disagrees with the manual, one of them must be wrong; that is a bug.

For problems with packages that are not part of Emacs, it is better to begin by reporting them to the package developers.

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3.3 Understanding Bug Reporting

When you decide that there is a bug, it is important to report it and to report it in a way which is useful. What is most useful is an exact description of what commands you type, starting with the shell command to run Emacs, until the problem happens.

The most important principle in reporting a bug is to report facts. Hypotheses and verbal descriptions are no substitute for the detailed raw data. Reporting the facts is straightforward, but many people strain to posit explanations and report them instead of the facts. If the explanations are based on guesses about how Emacs is implemented, they will be useless; meanwhile, lacking the facts, we will have no real information about the bug. If you want to actually debug the problem, and report explanations that are more than guesses, that is useful—but please include the raw facts as well.

For example, suppose that you type C-x C-f /glorp/baz.ugh <RET>, visiting a file which (you know) happens to be rather large, and Emacs displays ‘I feel pretty today’. The bug report would need to provide all that information. You should not assume that the problem is due to the size of the file and say, “I visited a large file, and Emacs displayed ‘I feel pretty today’.” This is what we mean by “guessing explanations”. The problem might be due to the fact that there is a ‘z’ in the file name. If this is so, then when we got your report, we would try out the problem with some large file, probably with no ‘z’ in its name, and not see any problem. There is no way we could guess that we should try visiting a file with a ‘z’ in its name.

You should not even say “visit a file” instead of C-x C-f. Similarly, rather than saying “if I have three characters on the line”, say “after I type <RET> A B C <RET> C-p”, if that is the way you entered the text.

If possible, try quickly to reproduce the bug by invoking Emacs with emacs -Q (so that Emacs starts with no initial customizations; @pxref{Initial Options}), and repeating the steps that you took to trigger the bug. If you can reproduce the bug this way, that rules out bugs in your personal customizations. Then your bug report should begin by stating that you started Emacs with emacs -Q, followed by the exact sequence of steps for reproducing the bug. If possible, inform us of the exact contents of any file that is needed to reproduce the bug.

Some bugs are not reproducible from emacs -Q; some are not easily reproducible at all. In that case, you should report what you have—but, as before, please stick to the raw facts about what you did to trigger the bug the first time.

If you have multiple issues that you want to report, please make a separate bug report for each.

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3.4 Checklist for Bug Reports

Before reporting a bug, first try to see if the problem has already been reported (see section Reading Existing Bug Reports and Known Problems).

If you are able to, try the latest release of Emacs to see if the problem has already been fixed. Even better is to try the latest development version. We recognize that this is not easy for some people, so do not feel that you absolutely must do this before making a report.

The best way to write a bug report for Emacs is to use the command M-x report-emacs-bug. This sets up a mail buffer (@pxref{Sending Mail}) and automatically inserts some of the essential information. However, it cannot supply all the necessary information; you should still read and follow the guidelines below, so you can enter the other crucial information by hand before you send the message. You may feel that some of the information inserted by M-x report-emacs-bug is not relevant, but unless you are absolutely sure it is best to leave it, so that the developers can decide for themselves.

When you have finished writing your report, type C-c C-c and it will be sent to the Emacs maintainers at bug-gnu-emacs. (If you want to suggest an improvement or new feature, use the same address.) If you cannot send mail from inside Emacs, you can copy the text of your report to your normal mail client (if your system supports it, you can type C-c M-i to have Emacs do this for you) and send it to that address. Or you can simply send an email to that address describing the problem.

Your report will be sent to the ‘bug-gnu-emacs’ mailing list, and stored in the GNU Bug Tracker at https://debbugs.gnu.org. Please include a valid reply email address, in case we need to ask you for more information about your report. Submissions are moderated, so there may be a delay before your report appears.

You do not need to know how the GNU Bug Tracker works in order to report a bug, but if you want to, you can read the tracker’s online documentation to see the various features you can use.

All mail sent to the ‘bug-gnu-emacs’ mailing list is also gatewayed to the ‘gnu.emacs.bug’ newsgroup. The reverse is also true, but we ask you not to post bug reports (or replies) via the newsgroup. It can make it much harder to contact you if we need to ask for more information, and it does not integrate well with the bug tracker.

If your data is more than 500,000 bytes, please don’t include it directly in the bug report; instead, offer to send it on request, or make it available online and say where.

The GNU Bug Tracker will assign a bug number to your report; please use it in the following discussions.

To enable maintainers to investigate a bug, your report should include all these things:

Here are some things that are not necessary in a bug report:

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3.5 Sending Patches for GNU Emacs

If you would like to write bug fixes or improvements for GNU Emacs, that is very helpful. When you send your changes, please follow these guidelines to make it easy for the maintainers to use them. If you don’t follow these guidelines, your information might still be useful, but using it will take extra work. Maintaining GNU Emacs is a lot of work in the best of circumstances, and we can’t keep up unless you do your best to help.

Every patch must have several pieces of information before we can properly evaluate it.

When you have all these pieces, bundle them up in a mail message and send it to the developers. Sending it to bug-gnu-emacs@gnu.org (which is the bug/feature list) is recommended, because that list is coupled to a tracking system that makes it easier to locate patches. If your patch is not complete and you think it needs more discussion, you might want to send it to emacs-devel@gnu.org instead. If you revise your patch, send it as a followup to the initial topic.

We prefer to get the patches as plain text, either inline (be careful your mail client does not change line breaks) or as MIME attachments.

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4 Contributing to Emacs Development

Emacs is a collaborative project and we encourage contributions from anyone and everyone.

There are many ways to contribute to Emacs:

If you would like to work on improving Emacs, please contact the maintainers at the emacs-devel mailing list. You can ask for suggested projects or suggest your own ideas.

If you have already written an improvement, please tell us about it. If you have not yet started work, it is useful to contact emacs-devel before you start; it might be possible to suggest ways to make your extension fit in better with the rest of Emacs.

When implementing a feature, please follow the Emacs coding standards; See section Coding Standards. In addition, non-trivial contributions require a copyright assignment to the FSF; See section Copyright Assignment.

The development version of Emacs can be downloaded from the repository where it is actively maintained by a group of developers. See the Emacs project page https://savannah.gnu.org/projects/emacs/ for access details.

It is important to write your patch based on the current working version. If you start from an older version, your patch may be outdated (so that maintainers will have a hard time applying it), or changes in Emacs may have made your patch unnecessary. After you have downloaded the repository source, you should read the file ‘INSTALL.REPO’ for build instructions (they differ to some extent from a normal build).

If you would like to make more extensive contributions, see the ‘CONTRIBUTE’ file in the Emacs distribution for information on how to be an Emacs developer.

For documentation on Emacs (to understand how to implement your desired change), refer to:

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4.1 Coding Standards

Contributed code should follow the GNU Coding Standards https://www.gnu.org/prep/standards/. This may also be available in info on your system.

If it doesn’t, we’ll need to find someone to fix the code before we can use it.

Emacs has additional style and coding conventions:

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4.2 Copyright Assignment

The FSF (Free Software Foundation) is the copyright holder for GNU Emacs. The FSF is a nonprofit with a worldwide mission to promote computer user freedom and to defend the rights of all free software users. For general information, see the website https://www.fsf.org/.

Generally speaking, for non-trivial contributions to GNU Emacs and packages stored in GNU ELPA, we require that the copyright be assigned to the FSF. For the reasons behind this, see https://www.gnu.org/licenses/why-assign.html.

Copyright assignment is a simple process. Residents of some countries can do it entirely electronically. We can help you get started, and answer any questions you may have (or point you to the people with the answers), at the emacs-devel@gnu.org mailing list.

(Please note: general discussion about why some GNU projects ask for a copyright assignment is off-topic for emacs-devel. See gnu-misc-discuss instead.)

A copyright disclaimer is also a possibility, but we prefer an assignment. Note that the disclaimer, like an assignment, involves you sending signed paperwork to the FSF (simply saying “this is in the public domain” is not enough). Also, a disclaimer cannot be applied to future work, it has to be repeated each time you want to send something new.

We can accept small changes (roughly, fewer than 15 lines) without an assignment. This is a cumulative limit (e.g., three separate 5 line patches) over all your contributions.

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5 How To Get Help with GNU Emacs

If you need help installing, using or changing GNU Emacs, there are two ways to find it:

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About This Document

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where the Example assumes that the current position is at Subsubsection One-Two-Three of a document of the following structure:

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