GNU Flymake

This manual is for GNU Flymake (version 0.3, April 2004), which is a universal on-the-fly syntax checker for GNU Emacs.

Copyright © 2004–2017 Free Software Foundation, Inc.

Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover Texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled “GNU Free Documentation License”.

(a) The FSF's Back-Cover Text is: “You have the freedom to copy and modify this GNU manual.”

Overview of Flymake
Installing Flymake
Using Flymake
Configuring Flymake
Flymake Implementation
GNU Free Documentation License

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1 Overview

Flymake is a universal on-the-fly syntax checker implemented as an Emacs minor mode. Flymake runs the pre-configured syntax check tool (compiler for C++ files, perl for perl files, etc.) in the background, passing it a temporary copy of the current buffer, and parses the output for known error/warning message patterns. Flymake then highlights erroneous lines (i.e., lines for which at least one error or warning has been reported by the syntax check tool), and displays an overall buffer status in the mode line. Status information displayed by Flymake contains total number of errors and warnings reported for the buffer during the last syntax check.

flymake-goto-next-error and flymake-goto-prev-error functions allow for easy navigation to the next/previous erroneous line, respectively.

Calling flymake-display-err-menu-for-current-line will popup a menu containing error messages reported by the syntax check tool for the current line. Errors/warnings belonging to another file, such as a .h header file included by a .c file, are shown in the current buffer as belonging to the first line. Menu items for such messages also contain a filename and a line number. Selecting such a menu item will automatically open the file and jump to the line with error.

Syntax check is done “on-the-fly”. It is started whenever

Flymake is a universal syntax checker in the sense that it's easily extended to support new syntax check tools and error message patterns. See Configuring Flymake.

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2 Installing

Flymake is packaged in a single file, flymake.el.

To install/update Flymake, place flymake.el to a directory somewhere on Emacs load path. You might also want to byte-compile flymake.el to improve performance.

Also, place the following line in the .emacs file.

     (require 'flymake)

You might also map the most frequently used Flymake functions, such as flymake-goto-next-error, to some keyboard shortcuts:

     (global-set-key [f3] 'flymake-display-err-menu-for-current-line)
     (global-set-key [f4] 'flymake-goto-next-error)

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3 Using Flymake

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3.1 Flymake mode

Flymake is an Emacs minor mode. To use Flymake, you must first activate flymake-mode by using the flymake-mode function.

Instead of manually activating flymake-mode, you can configure Flymake to automatically enable flymake-mode upon opening any file for which syntax check is possible. To do so, place the following line in .emacs:

     (add-hook 'find-file-hook 'flymake-find-file-hook)

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3.2 Running the syntax check

When flymake-mode is active, syntax check is started automatically on any of the three conditions mentioned above. Syntax check can also be started manually by using the flymake-start-syntax-check-for-current-buffer function. This can be used, for example, when changes were made to some other buffer affecting the current buffer.

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3.3 Navigating to error lines

After syntax check is completed, lines for which at least one error or warning has been reported are highlighted, and total number of errors and warning is shown in the mode line. Use the following functions to navigate the highlighted lines.

flymake-goto-next-error Moves point to the next erroneous line, if any.

flymake-goto-prev-error Moves point to the previous erroneous line.

These functions treat erroneous lines as a linked list. Therefore, flymake-goto-next-error will go to the first erroneous line when invoked in the end of the buffer.

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3.4 Viewing error messages

To view error messages belonging to the current line, use the flymake-display-err-menu-for-current-line function. If there's at least one error or warning reported for the current line, this function will display a popup menu with error/warning texts. Selecting the menu item whose error belongs to another file brings forward that file with the help of the flymake-goto-file-and-line function.

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3.5 Syntax check statuses

After syntax check is finished, its status is displayed in the mode line. The following statuses are defined.

Flymake* or Flymake:E/W* Flymake is currently running. For the second case, E/W contains the error and warning count for the previous run.

Flymake Syntax check is not running. Usually this means syntax check was successfully passed (no errors, no warnings). Other possibilities are: syntax check was killed as a result of executing flymake-compile, or syntax check cannot start as compilation is currently in progress.

Flymake:E/W Number of errors/warnings found by the syntax check process.

Flymake:! Flymake was unable to find master file for the current buffer.

The following errors cause a warning message and switch flymake mode OFF for the buffer.

CFGERR Syntax check process returned nonzero exit code, but no errors/warnings were reported. This indicates a possible configuration error (for example, no suitable error message patterns for the syntax check tool).

NOMASTER Flymake was unable to find master file for the current buffer.

NOMK Flymake was unable to find a suitable buildfile for the current buffer.

PROCERR Flymake was unable to launch a syntax check process.

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3.6 Troubleshooting

Flymake uses a simple logging facility for indicating important points in the control flow. The logging facility sends logging messages to the *Messages* buffer. The information logged can be used for resolving various problems related to Flymake.

Logging output is controlled by the flymake-log-level variable. 3 is the most verbose level, and -1 switches logging off.

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4 Configuring and Extending Flymake

Flymake was designed to be easily extended for supporting new syntax check tools and error message patterns.

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4.1 Customizable variables

This section summarizes variables used for Flymake configuration.

Controls logging output, see Troubleshooting.
A list of (filename-regexp, init-function, cleanup-function getfname-function) for configuring syntax check tools. See Adding support for a new syntax check tool.
A list of directories for searching a master file. See Locating a master file.
A function used for obtaining a list of project include dirs (C/C++ specific). See Getting the include directories.
Used when looking for a master file. See Locating a master file.
Patterns for error/warning messages in the form (regexp file-idx line-idx col-idx err-text-idx). See Parsing the output.
Predicate to classify error text as warning. See Parsing the output.
A flag indicating whether compilation and syntax check of the same file cannot be run simultaneously.
If any changes are made to the buffer, syntax check is automatically started after flymake-no-changes-timeout seconds.
A boolean flag indicating whether Flymake will show message boxes for non-recoverable errors. If flymake-gui-warnings-enabled is nil, these errors will only be logged to the *Messages* buffer.
A boolean flag indicating whether to start syntax check after a newline character is added to the buffer.
A custom face for highlighting lines for which at least one error has been reported.
A custom face for highlighting lines for which at least one warning and no errors have been reported.
A bitmap used in the fringe to mark lines for which an error has been reported.
A bitmap used in the fringe to mark lines for which a warning has been reported.
Which fringe (if any) should show the warning/error bitmaps.

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4.2 Adding support for a new syntax check tool

Syntax check tools are configured using the flymake-allowed-file-name-masks list. Each item of this list has the following format:

     (filename-regexp, init-function, cleanup-function, getfname-function)
This field is used as a key for locating init/cleanup/getfname functions for the buffer. Items in flymake-allowed-file-name-masks are searched sequentially. The first item with filename-regexp matching buffer filename is selected. If no match is found, flymake-mode is switched off.
init-function is required to initialize the syntax check, usually by creating a temporary copy of the buffer contents. The function must return (list cmd-name arg-list). If init-function returns null, syntax check is aborted, by flymake-mode is not switched off.
cleanup-function is called after the syntax check process is complete and should take care of proper deinitialization, which is usually deleting a temporary copy created by the init-function.
This function is used for translating filenames reported by the syntax check tool into “real” filenames. Filenames reported by the tool will be different from the real ones, as actually the tool works with the temporary copy. In most cases, the default implementation provided by Flymake, flymake-get-real-file-name, can be used as getfname-function.

To add support for a new syntax check tool, write corresponding init-function, and, optionally cleanup-function and getfname-function. If the format of error messages reported by the new tool is not yet supported by Flymake, add a new entry to the flymake-err-line-patterns list.

The following sections contain some examples of configuring Flymake support for various syntax check tools.

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4.2.1 Example—Configuring a tool called directly

In this example, we will add support for perl as a syntax check tool. perl supports the -c option which does syntax checking.

First, we write the init-function:

     (defun flymake-perl-init ()
       (let* ((temp-file (flymake-init-create-temp-buffer-copy
              (local-file (file-relative-name
                           (file-name-directory buffer-file-name))))
         (list "perl" (list "-wc " local-file))))

flymake-perl-init creates a temporary copy of the buffer contents with the help of flymake-init-create-temp-buffer-copy, and builds an appropriate command line.

Next, we add a new entry to the flymake-allowed-file-name-masks:

     (setq flymake-allowed-file-name-masks
           (cons '(".+\\.pl$"

Note that we use standard cleanup-function and getfname-function.

Finally, we add an entry to flymake-err-line-patterns:

     (setq flymake-err-line-patterns
           (cons '("\\(.*\\) at \\([^ \n]+\\) line \\([0-9]+\\)[,.\n]"
                   2 3 nil 1)

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4.2.2 Example—Configuring a tool called via make

In this example we will add support for C files syntax checked by gcc called via make.

We're not required to write any new functions, as Flymake already has functions for make. We just add a new entry to the flymake-allowed-file-name-masks:

     (setq flymake-allowed-file-name-masks
           (cons '(".+\\.c$"

flymake-simple-make-init builds the following make command line:

     (list "make"
           (list "-s" "-C"
                 (concat "CHK_SOURCES=" source)

base-dir is a directory containing Makefile, see Locating the buildfile.

Thus, Makefile must contain the check-syntax target. In our case this target might look like this:

	gcc -o /dev/null -S ${CHK_SOURCES}

The format of error messages reported by gcc is already supported by Flymake, so we don't have to add a new entry to flymake-err-line-patterns. Note that if you are using Automake, you may want to replace gcc with the standard Automake variable COMPILE:

	$(COMPILE) -o /dev/null -S ${CHK_SOURCES}

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5 Flymake Implementation

Syntax check is started by calling flymake-start-syntax-check-for-current-buffer. Flymake first determines whether it is able to do syntax check. It then saves a copy of the buffer in a temporary file in the buffer's directory (or in the system temp directory, for java files), creates a syntax check command and launches a process with this command. The output is parsed using a list of error message patterns, and error information (file name, line number, type and text) is saved. After the process has finished, Flymake highlights erroneous lines in the buffer using the accumulated error information.

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5.1 Determining whether syntax check is possible

Syntax check is considered possible if there's an entry in flymake-allowed-file-name-masks matching buffer's filename and its init-function returns non-nil value.

Two syntax check modes are distinguished:

  1. Buffer can be syntax checked in a standalone fashion, that is, the file (its temporary copy, in fact) can be passed over to the compiler to do the syntax check. Examples are C/C++ (.c, .cpp) and Java (.java) sources.
  2. Buffer can be syntax checked, but additional file, called master file, is required to perform this operation. A master file is a file that includes the current file, so that running a syntax check tool on it will also check syntax in the current file. Examples are C/C++ (.h, .hpp) headers.

These modes are handled inside init/cleanup/getfname functions, see Adding support for a new syntax check tool.

Flymake contains implementations of all functionality required to support different syntax check modes described above (making temporary copies, finding master files, etc.), as well as some tool-specific (routines for Make, Ant, etc.) code.

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5.2 Making a temporary copy

After the possibility of the syntax check has been determined, a temporary copy of the current buffer is made so that the most recent unsaved changes could be seen by the syntax check tool. Making a copy is quite straightforward in a standalone case (mode 1), as it's just saving buffer contents to a temporary file.

Things get trickier, however, when master file is involved, as it requires to

Locating a master file is discussed in the following section.

Patching just changes all appropriate lines of the master file so that they use the new (temporary) name of the current file. For example, suppose current file name is file.h, the master file is file.cpp, and it includes current file via #include "file.h". Current file's copy is saved to file file_flymake.h, so the include line must be changed to #include "file_flymake.h". Finally, patched master file is saved to file_flymake_master.cpp, and the last one is passed to the syntax check tool.

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5.3 Locating a master file

Master file is located in two steps.

First, a list of possible master files is built. A simple name matching is used to find the files. For a C++ header file.h, Flymake searches for all .cpp files in the directories whose relative paths are stored in a customizable variable flymake-master-file-dirs, which usually contains something like ("." "./src"). No more than flymake-master-file-count-limit entries is added to the master file list. The list is then sorted to move files with names file.cpp to the top.

Next, each master file in a list is checked to contain the appropriate include directives. No more than flymake-check-file-limit of each file are parsed.

For file.h, the include directives to look for are #include "file.h", #include "../file.h", etc. Each include is checked against a list of include directories (see Getting the include directories) to be sure it points to the correct file.h.

First matching master file found stops the search. The master file is then patched and saved to disk. In case no master file is found, syntax check is aborted, and corresponding status (!) is reported in the mode line.

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5.4 Getting the include directories

Two sets of include directories are distinguished: system include directories and project include directories. The former is just the contents of the INCLUDE environment variable. The latter is not so easy to obtain, and the way it can be obtained can vary greatly for different projects. Therefore, a customizable variable flymake-get-project-include-dirs-function is used to provide the way to implement the desired behavior.

The default implementation, flymake-get-project-include-dirs-imp, uses a make call. This requires a correct base directory, that is, a directory containing a correct Makefile, to be determined.

As obtaining the project include directories might be a costly operation, its return value is cached in the hash table. The cache is cleared in the beginning of every syntax check attempt.

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5.5 Locating the buildfile

Flymake can be configured to use different tools for performing syntax checks. For example, it can use direct compiler call to syntax check a perl script or a call to make for a more complicated case of a C/C++ source. The general idea is that simple files, like perl scripts and html pages, can be checked by directly invoking a corresponding tool. Files that are usually more complex and generally used as part of larger projects, might require non-trivial options to be passed to the syntax check tool, like include directories for C++. The latter files are syntax checked using some build tool, like Make or Ant.

All Make configuration data is usually stored in a file called Makefile. To allow for future extensions, flymake uses a notion of buildfile to reference the 'project configuration' file.

Special function, flymake-find-buildfile is provided for locating buildfiles. Searching for a buildfile is done in a manner similar to that of searching for possible master files. In case there's no build file, syntax check is aborted.

Buildfile values are also cached.

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5.6 Starting the syntax check process

The command line (command name and the list of arguments) for launching a process is returned by the initialization function. Flymake then just calls start-process to start an asynchronous process and configures a process filter and sentinel, which are used for processing the output of the syntax check tool.

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5.7 Parsing the output

The output generated by the syntax check tool is parsed in the process filter/sentinel using the error message patterns stored in the flymake-err-line-patterns variable. This variable contains a list of items of the form (regexp file-idx line-idx err-text-idx), used to determine whether a particular line is an error message and extract file name, line number and error text, respectively. Error type (error/warning) is also guessed by matching error text with the '^[wW]arning' pattern. Anything that was not classified as a warning is considered an error. Type is then used to sort error menu items, which shows error messages first.

Flymake is also able to interpret error message patterns missing err-text-idx information. This is done by merely taking the rest of the matched line ((substring line (match-end 0))) as error text. This trick allows making use of a huge collection of error message line patterns from compile.el. All these error patterns are appended to the end of flymake-err-line-patterns.

The error information obtained is saved in a buffer local variable. The buffer for which the process output belongs is determined from the process-id->buffer mapping updated after every process launch/exit.

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5.8 Highlighting erroneous lines

Highlighting is implemented with overlays and happens in the process sentinel, after calling the cleanup function. Two customizable faces are used: flymake-errline and flymake-warnline. Errors belonging outside the current buffer are considered to belong to line 1 of the current buffer.

If the option flymake-fringe-indicator-position is non-nil, errors and warnings are also highlighted in the left or right fringe, using the bitmaps specified by flymake-error-bitmap and flymake-warning-bitmap.

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5.9 Interaction with other modes

The only mode flymake currently knows about is compile.

Flymake can be configured to not start syntax check if it thinks the compilation is in progress. The check is made by the flymake-compilation-is-running, which tests the compilation-in-progress variable. The reason why this might be useful is saving CPU time in case both syntax check and compilation are very CPU intensive. The original reason for adding this feature, though, was working around a locking problem with MS Visual C++ compiler.

Flymake also provides an alternative command for starting compilation, flymake-compile:

     (defun flymake-compile ()
       "Kill all flymake syntax checks then start compilation."
       (call-interactively 'compile))

It just kills all the active syntax check processes before calling compile.

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Appendix A GNU Free Documentation License

Version 1.3, 3 November 2008
     Copyright © 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

    The purpose of this License is to make a manual, textbook, or other functional and useful document free in the sense of freedom: to assure everyone the effective freedom to copy and redistribute it, with or without modifying it, either commercially or noncommercially. Secondarily, this License preserves for the author and publisher a way to get credit for their work, while not being considered responsible for modifications made by others.

    This License is a kind of “copyleft”, which means that derivative works of the document must themselves be free in the same sense. It complements the GNU General Public License, which is a copyleft license designed for free software.

    We have designed this License in order to use it for manuals for free software, because free software needs free documentation: a free program should come with manuals providing the same freedoms that the software does. But this License is not limited to software manuals; it can be used for any textual work, regardless of subject matter or whether it is published as a printed book. We recommend this License principally for works whose purpose is instruction or reference.


    This License applies to any manual or other work, in any medium, that contains a notice placed by the copyright holder saying it can be distributed under the terms of this License. Such a notice grants a world-wide, royalty-free license, unlimited in duration, to use that work under the conditions stated herein. The “Document”, below, refers to any such manual or work. Any member of the public is a licensee, and is addressed as “you”. You accept the license if you copy, modify or distribute the work in a way requiring permission under copyright law.

    A “Modified Version” of the Document means any work containing the Document or a portion of it, either copied verbatim, or with modifications and/or translated into another language.

    A “Secondary Section” is a named appendix or a front-matter section of the Document that deals exclusively with the relationship of the publishers or authors of the Document to the Document's overall subject (or to related matters) and contains nothing that could fall directly within that overall subject. (Thus, if the Document is in part a textbook of mathematics, a Secondary Section may not explain any mathematics.) The relationship could be a matter of historical connection with the subject or with related matters, or of legal, commercial, philosophical, ethical or political position regarding them.

    The “Invariant Sections” are certain Secondary Sections whose titles are designated, as being those of Invariant Sections, in the notice that says that the Document is released under this License. If a section does not fit the above definition of Secondary then it is not allowed to be designated as Invariant. The Document may contain zero Invariant Sections. If the Document does not identify any Invariant Sections then there are none.

    The “Cover Texts” are certain short passages of text that are listed, as Front-Cover Texts or Back-Cover Texts, in the notice that says that the Document is released under this License. A Front-Cover Text may be at most 5 words, and a Back-Cover Text may be at most 25 words.

    A “Transparent” copy of the Document means a machine-readable copy, represented in a format whose specification is available to the general public, that is suitable for revising the document straightforwardly with generic text editors or (for images composed of pixels) generic paint programs or (for drawings) some widely available drawing editor, and that is suitable for input to text formatters or for automatic translation to a variety of formats suitable for input to text formatters. A copy made in an otherwise Transparent file format whose markup, or absence of markup, has been arranged to thwart or discourage subsequent modification by readers is not Transparent. An image format is not Transparent if used for any substantial amount of text. A copy that is not “Transparent” is called “Opaque”.

    Examples of suitable formats for Transparent copies include plain ASCII without markup, Texinfo input format, LaTeX input format, SGML or XML using a publicly available DTD, and standard-conforming simple HTML, PostScript or PDF designed for human modification. Examples of transparent image formats include PNG, XCF and JPG. Opaque formats include proprietary formats that can be read and edited only by proprietary word processors, SGML or XML for which the DTD and/or processing tools are not generally available, and the machine-generated HTML, PostScript or PDF produced by some word processors for output purposes only.

    The “Title Page” means, for a printed book, the title page itself, plus such following pages as are needed to hold, legibly, the material this License requires to appear in the title page. For works in formats which do not have any title page as such, “Title Page” means the text near the most prominent appearance of the work's title, preceding the beginning of the body of the text.

    The “publisher” means any person or entity that distributes copies of the Document to the public.

    A section “Entitled XYZ” means a named subunit of the Document whose title either is precisely XYZ or contains XYZ in parentheses following text that translates XYZ in another language. (Here XYZ stands for a specific section name mentioned below, such as “Acknowledgements”, “Dedications”, “Endorsements”, or “History”.) To “Preserve the Title” of such a section when you modify the Document means that it remains a section “Entitled XYZ” according to this definition.

    The Document may include Warranty Disclaimers next to the notice which states that this License applies to the Document. These Warranty Disclaimers are considered to be included by reference in this License, but only as regards disclaiming warranties: any other implication that these Warranty Disclaimers may have is void and has no effect on the meaning of this License.


    You may copy and distribute the Document in any medium, either commercially or noncommercially, provided that this License, the copyright notices, and the license notice saying this License applies to the Document are reproduced in all copies, and that you add no other conditions whatsoever to those of this License. You may not use technical measures to obstruct or control the reading or further copying of the copies you make or distribute. However, you may accept compensation in exchange for copies. If you distribute a large enough number of copies you must also follow the conditions in section 3.

    You may also lend copies, under the same conditions stated above, and you may publicly display copies.


    If you publish printed copies (or copies in media that commonly have printed covers) of the Document, numbering more than 100, and the Document's license notice requires Cover Texts, you must enclose the copies in covers that carry, clearly and legibly, all these Cover Texts: Front-Cover Texts on the front cover, and Back-Cover Texts on the back cover. Both covers must also clearly and legibly identify you as the publisher of these copies. The front cover must present the full title with all words of the title equally prominent and visible. You may add other material on the covers in addition. Copying with changes limited to the covers, as long as they preserve the title of the Document and satisfy these conditions, can be treated as verbatim copying in other respects.

    If the required texts for either cover are too voluminous to fit legibly, you should put the first ones listed (as many as fit reasonably) on the actual cover, and continue the rest onto adjacent pages.

    If you publish or distribute Opaque copies of the Document numbering more than 100, you must either include a machine-readable Transparent copy along with each Opaque copy, or state in or with each Opaque copy a computer-network location from which the general network-using public has access to download using public-standard network protocols a complete Transparent copy of the Document, free of added material. If you use the latter option, you must take reasonably prudent steps, when you begin distribution of Opaque copies in quantity, to ensure that this Transparent copy will remain thus accessible at the stated location until at least one year after the last time you distribute an Opaque copy (directly or through your agents or retailers) of that edition to the public.

    It is requested, but not required, that you contact the authors of the Document well before redistributing any large number of copies, to give them a chance to provide you with an updated version of the Document.


    You may copy and distribute a Modified Version of the Document under the conditions of sections 2 and 3 above, provided that you release the Modified Version under precisely this License, with the Modified Version filling the role of the Document, thus licensing distribution and modification of the Modified Version to whoever possesses a copy of it. In addition, you must do these things in the Modified Version:

    1. Use in the Title Page (and on the covers, if any) a title distinct from that of the Document, and from those of previous versions (which should, if there were any, be listed in the History section of the Document). You may use the same title as a previous version if the original publisher of that version gives permission.
    2. List on the Title Page, as authors, one or more persons or entities responsible for authorship of the modifications in the Modified Version, together with at least five of the principal authors of the Document (all of its principal authors, if it has fewer than five), unless they release you from this requirement.
    3. State on the Title page the name of the publisher of the Modified Version, as the publisher.
    4. Preserve all the copyright notices of the Document.
    5. Add an appropriate copyright notice for your modifications adjacent to the other copyright notices.
    6. Include, immediately after the copyright notices, a license notice giving the public permission to use the Modified Version under the terms of this License, in the form shown in the Addendum below.
    7. Preserve in that license notice the full lists of Invariant Sections and required Cover Texts given in the Document's license notice.
    8. Include an unaltered copy of this License.
    9. Preserve the section Entitled “History”, Preserve its Title, and add to it an item stating at least the title, year, new authors, and publisher of the Modified Version as given on the Title Page. If there is no section Entitled “History” in the Document, create one stating the title, year, authors, and publisher of the Document as given on its Title Page, then add an item describing the Modified Version as stated in the previous sentence.
    10. Preserve the network location, if any, given in the Document for public access to a Transparent copy of the Document, and likewise the network locations given in the Document for previous versions it was based on. These may be placed in the “History” section. You may omit a network location for a work that was published at least four years before the Document itself, or if the original publisher of the version it refers to gives permission.
    11. For any section Entitled “Acknowledgements” or “Dedications”, Preserve the Title of the section, and preserve in the section all the substance and tone of each of the contributor acknowledgements and/or dedications given therein.
    12. Preserve all the Invariant Sections of the Document, unaltered in their text and in their titles. Section numbers or the equivalent are not considered part of the section titles.
    13. Delete any section Entitled “Endorsements”. Such a section may not be included in the Modified Version.
    14. Do not retitle any existing section to be Entitled “Endorsements” or to conflict in title with any Invariant Section.
    15. Preserve any Warranty Disclaimers.

    If the Modified Version includes new front-matter sections or appendices that qualify as Secondary Sections and contain no material copied from the Document, you may at your option designate some or all of these sections as invariant. To do this, add their titles to the list of Invariant Sections in the Modified Version's license notice. These titles must be distinct from any other section titles.

    You may add a section Entitled “Endorsements”, provided it contains nothing but endorsements of your Modified Version by various parties—for example, statements of peer review or that the text has been approved by an organization as the authoritative definition of a standard.

    You may add a passage of up to five words as a Front-Cover Text, and a passage of up to 25 words as a Back-Cover Text, to the end of the list of Cover Texts in the Modified Version. Only one passage of Front-Cover Text and one of Back-Cover Text may be added by (or through arrangements made by) any one entity. If the Document already includes a cover text for the same cover, previously added by you or by arrangement made by the same entity you are acting on behalf of, you may not add another; but you may replace the old one, on explicit permission from the previous publisher that added the old one.

    The author(s) and publisher(s) of the Document do not by this License give permission to use their names for publicity for or to assert or imply endorsement of any Modified Version.


    You may combine the Document with other documents released under this License, under the terms defined in section 4 above for modified versions, provided that you include in the combination all of the Invariant Sections of all of the original documents, unmodified, and list them all as Invariant Sections of your combined work in its license notice, and that you preserve all their Warranty Disclaimers.

    The combined work need only contain one copy of this License, and multiple identical Invariant Sections may be replaced with a single copy. If there are multiple Invariant Sections with the same name but different contents, make the title of each such section unique by adding at the end of it, in parentheses, the name of the original author or publisher of that section if known, or else a unique number. Make the same adjustment to the section titles in the list of Invariant Sections in the license notice of the combined work.

    In the combination, you must combine any sections Entitled “History” in the various original documents, forming one section Entitled “History”; likewise combine any sections Entitled “Acknowledgements”, and any sections Entitled “Dedications”. You must delete all sections Entitled “Endorsements.”


    You may make a collection consisting of the Document and other documents released under this License, and replace the individual copies of this License in the various documents with a single copy that is included in the collection, provided that you follow the rules of this License for verbatim copying of each of the documents in all other respects.

    You may extract a single document from such a collection, and distribute it individually under this License, provided you insert a copy of this License into the extracted document, and follow this License in all other respects regarding verbatim copying of that document.


    A compilation of the Document or its derivatives with other separate and independent documents or works, in or on a volume of a storage or distribution medium, is called an “aggregate” if the copyright resulting from the compilation is not used to limit the legal rights of the compilation's users beyond what the individual works permit. When the Document is included in an aggregate, this License does not apply to the other works in the aggregate which are not themselves derivative works of the Document.

    If the Cover Text requirement of section 3 is applicable to these copies of the Document, then if the Document is less than one half of the entire aggregate, the Document's Cover Texts may be placed on covers that bracket the Document within the aggregate, or the electronic equivalent of covers if the Document is in electronic form. Otherwise they must appear on printed covers that bracket the whole aggregate.


    Translation is considered a kind of modification, so you may distribute translations of the Document under the terms of section 4. Replacing Invariant Sections with translations requires special permission from their copyright holders, but you may include translations of some or all Invariant Sections in addition to the original versions of these Invariant Sections. You may include a translation of this License, and all the license notices in the Document, and any Warranty Disclaimers, provided that you also include the original English version of this License and the original versions of those notices and disclaimers. In case of a disagreement between the translation and the original version of this License or a notice or disclaimer, the original version will prevail.

    If a section in the Document is Entitled “Acknowledgements”, “Dedications”, or “History”, the requirement (section 4) to Preserve its Title (section 1) will typically require changing the actual title.


    You may not copy, modify, sublicense, or distribute the Document except as expressly provided under this License. Any attempt otherwise to copy, modify, sublicense, or distribute it is void, and will automatically terminate your rights under this License.

    However, if you cease all violation of this License, then your license from a particular copyright holder is reinstated (a) provisionally, unless and until the copyright holder explicitly and finally terminates your license, and (b) permanently, if the copyright holder fails to notify you of the violation by some reasonable means prior to 60 days after the cessation.

    Moreover, your license from a particular copyright holder is reinstated permanently if the copyright holder notifies you of the violation by some reasonable means, this is the first time you have received notice of violation of this License (for any work) from that copyright holder, and you cure the violation prior to 30 days after your receipt of the notice.

    Termination of your rights under this section does not terminate the licenses of parties who have received copies or rights from you under this License. If your rights have been terminated and not permanently reinstated, receipt of a copy of some or all of the same material does not give you any rights to use it.


    The Free Software Foundation may publish new, revised versions of the GNU Free Documentation License from time to time. Such new versions will be similar in spirit to the present version, but may differ in detail to address new problems or concerns. See

    Each version of the License is given a distinguishing version number. If the Document specifies that a particular numbered version of this License “or any later version” applies to it, you have the option of following the terms and conditions either of that specified version or of any later version that has been published (not as a draft) by the Free Software Foundation. If the Document does not specify a version number of this License, you may choose any version ever published (not as a draft) by the Free Software Foundation. If the Document specifies that a proxy can decide which future versions of this License can be used, that proxy's public statement of acceptance of a version permanently authorizes you to choose that version for the Document.


    “Massive Multiauthor Collaboration Site” (or “MMC Site”) means any World Wide Web server that publishes copyrightable works and also provides prominent facilities for anybody to edit those works. A public wiki that anybody can edit is an example of such a server. A “Massive Multiauthor Collaboration” (or “MMC”) contained in the site means any set of copyrightable works thus published on the MMC site.

    “CC-BY-SA” means the Creative Commons Attribution-Share Alike 3.0 license published by Creative Commons Corporation, a not-for-profit corporation with a principal place of business in San Francisco, California, as well as future copyleft versions of that license published by that same organization.

    “Incorporate” means to publish or republish a Document, in whole or in part, as part of another Document.

    An MMC is “eligible for relicensing” if it is licensed under this License, and if all works that were first published under this License somewhere other than this MMC, and subsequently incorporated in whole or in part into the MMC, (1) had no cover texts or invariant sections, and (2) were thus incorporated prior to November 1, 2008.

    The operator of an MMC Site may republish an MMC contained in the site under CC-BY-SA on the same site at any time before August 1, 2009, provided the MMC is eligible for relicensing.

ADDENDUM: How to use this License for your documents

To use this License in a document you have written, include a copy of the License in the document and put the following copyright and license notices just after the title page:

       Copyright (C)  year  your name.
       Permission is granted to copy, distribute and/or modify this document
       under the terms of the GNU Free Documentation License, Version 1.3
       or any later version published by the Free Software Foundation;
       with no Invariant Sections, no Front-Cover Texts, and no Back-Cover
       Texts.  A copy of the license is included in the section entitled ``GNU
       Free Documentation License''.

If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts, replace the “with...Texts.” line with this:

         with the Invariant Sections being list their titles, with
         the Front-Cover Texts being list, and with the Back-Cover Texts
         being list.

If you have Invariant Sections without Cover Texts, or some other combination of the three, merge those two alternatives to suit the situation.

If your document contains nontrivial examples of program code, we recommend releasing these examples in parallel under your choice of free software license, such as the GNU General Public License, to permit their use in free software.

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