Table of Contents
*****************

LibreJS
1 Overview
2 Disclaimer
3 Installation
  3.1 Building the Package
  3.2 Installing LibreJS
4 How to Use
  4.1 LibreJS in action
  4.2 Complaint Feature
  4.3 Options
5 JavaScript Detection
6 Free Licenses Detection
  6.1 Detected Free Licenses
  6.2 Undetected Free Licenses
7 Setting Your JavaScript Free
  7.1 Adding a stylized comment in your JavaScript files and on your page
  7.2 JavaScript Web Labels
Appendix A Installation Requirements
  A.1 Mozilla Browser
  A.2 Mozilla's Add-on SDK
Appendix B LibreJS Internals
Appendix C Tests
Appendix D GNU Free Documentation License


LibreJS
*******

This manual is for GNU LibreJS (version 4.6, 5 May 2012).

1 Overview
**********

GNU LibreJS --an add-on for GNU IceCat and Mozilla Firefox-- detects
and blocks nonfree nontrivial JavaScript while allowing its execution on
pages containing code that is either trivial and/or free.

   Many websites run nontrivial JavaScript on your computer. Some use it
for complex tasks; many use it gratuitously for minor jobs that could be
done easily with plain HTML.  Sometimes this JavaScript code is
malicious.  Either way, the JavaScript code is often nonfree.  For
explanation of the issue, see "The JavaScript
Trap"(`http://www.gnu.org/philosophy/javascript-trap.html').

   If you care about freedom in your computing, and don't wish to let
all and sundry make you run nonfree programs, now you can prevent it by
using LibreJS.

2 Disclaimer
************

   * LibreJS is not a security tool. Its goal is to detect nonfree
     nontrivial JavaScript, and it currently does not detect whether
     free or trivial code is malicious or not. Other free Mozilla
     extensions and add-ons may be available for this purpose.

   * LibreJS is always a work in progress. If you find a bug, please
     report it to <lduros@gnu.org>.


3 Installation
**************

You may install LibreJS directly using a generated `librejs.xpi' file,
or by building it from source.

3.1 Building the Package
========================

After enabling the Add-on SDK, you should be able to use the `make'
command to build LibreJS from source.

   After running `make', a new file, `librejs.xpi' should be generated.
This is the file that can be installed in a Mozilla browser.

3.2 Installing LibreJS
======================

To install the add-on for all users, run:
     sudo make install

   or as root:
     make install

   Next time you open a Mozilla-browser as a user of your system, you
should be notified that a new add-on (in this case, LibreJS) as been
installed and whether to allow it to run or not.

4 How to Use
************

4.1 LibreJS in action
=====================

After installing the add-on, you will see the LibreJS widget in the
add-on bar at the bottom of the browser window.  After loading a page,
left-click on the widget to view the deactivated JavaScript code from
the page (both on page and external) and, if applicable, the scripts
that were accepted.

4.2 Complaint Feature
=====================

It is very important to complain when a site has nonfree JavaScript
code, especially if it won't work without that code.  LibreJS makes it
easy to complain by heuristically finding where to send the complaint.

   When nonfree/nontrivial code is detected in a page, LibreJS attempts
to find a relevant contact link or email for the website you are
visiting. In order to do so, it will attempt to visit a few links from
the current page (for instance, a link labeled "contact" on the same
domain as the current page, ...)

   LibreJS can currently detect and list contact pages with webforms,
email addresses more likely to be owned by the maintainer of the site,
Twitter and identi.ca links, phone numbers.

   After LibreJS detects one or more of the above, a small tab will
appear on the right of your screen with the LibreJS torch logo. When
hovering over the tab, a large panel will slide in with the contact
information. Ideally, at the top you will find the email address of the
maintainer, labeled as the "Email you should use".

   When you complain to the website for their nonfree nontrivial
JavaScript, provide them with the link to the JavaScript Trap essay so
that they can get more information on what the issue is and how they can
solve it on their own site.

4.3 Options
===========

   * LibreJS lets you whitelist domain names and subdomains to bypass
     the regular JavaScript check. This might be useful, for example,
     if you are running your own code in a local web server. In order
     to add a whitelisted domain or url, go to Tools >> Add-ons, or
     press `Control + Shift + A'. Inside the add-on window, click on
     "Extensions", and in the list, where you see LibreJS, click on the
     "Preferences" button.  You will see an input field labeled
     "Whitelist domain". In the field, enter comma-separated domain
     names. Do not enter the protocol. For instance to whitelist all
     the pages of `http://www.gnu.org' and `https://gnu.org', enter
     "gnu.org". To allow all subdomains from gnu.org, enter:
     "*.gnu.org". This will match such sites as
     `http://savannah.gnu.org' and `http://audio-video.gnu.org'.


5 JavaScript Detection
**********************

     LibreJS considers JavaScript on a page as nontrivial if:

   * it makes an AJAX request or is loaded along with scripts that make
     an AJAX request,

   * it loads external scripts dynamically or is loaded along with
     scripts that do,

   * it defines functions or methods and either loads an external script
     (from HTML) or is loaded as one,

   * it uses dynamic JavaScript constructs that are difficult to analyze
     without interpreting the program or is loaded along with scripts
     that use such constructs. These constructs are:
        * using the eval function,

        * calling methods with the square bracket notation,

        * using any other construct than a string literal with certain
          methods (`Obj.write', `Obj.createElement', ...).
In practice, the JavaScript code in your page may be found trivial by
LibreJS if, as a whole:
   * it does not defines functions and it does not load external scripts
     (with the HTML src attribute in a `<script>' tag);

   * it does not make AJAX calls;

   * it does not load external scripts with dynamic constructs;

   * it does not use constructs that may be used to do any of the above
     in a non-obvious way (use of the `eval()' method, use of square
     bracket method calls, use of concatenation with certain constructs
     or method calls, ...)


   However, in some instances, you may be required by LibreJS to add a
stylized comment to JavaScript code that may be otherwise trivial.

   When an external file defines a function/method, it becomes available
to all other external scripts. That is the case if another script
defines a function that makes AJAX calls, when an external script loads
other scripts dynamically (which in turn could also make AJAX calls,
...), or when a script is written with constructs that may do any of
these.

   For instance, if your page contains the following:
     <script src="jquery.js"></script>
     <script>
     $.doSomething();
     </script>

   While `$.doSomething();' may seem trivial, you will nevertheless
have to add a stylized license comment on your main HTML page because
the external script (in this case jQuery) has been found to define
methods that make AJAX calls. `$.doSomething()' might make an AJAX call,
and LibreJS does not check for that.  The rule of thumb is that when you
use a library or code that handles AJAX, JSON, JSONP, the loading of
scripts dynamically, you should have license mentions for all your
JavaScript files and for your main page regardless. In practice this is
a case that happens very often with code that uses libraries.

   In practice also, the JavaScript code in an external file (an
external `.js' file loaded on your page) may be found trivial if it
does not define functions/methods.

   And in the same manner it will be considered nontrivial if AJAX
calls, dynamic script loading, or non-obvious dynamic JavaScript
constructs are used in another script.

6 Free Licenses Detection
*************************

6.1 Detected Free Licenses
==========================

In order for a file to be detected as free, the license notice should
appear in a JavaScript file above all code, at the very top of the file.

   For inline JavaScript code inside `<script>' tags in HTML pages, the
license notice should appear once per page as a comment inside a
`<script>' tag, before all the code in that script. When the only
inline JavaScript code is within element attributes (`onload',
`onclick'), place the license notice in an otherwise empty `<script>'
at the top of the page. This is sometimes needed when an external
script performs AJAX calls or embeds scripts dynamically, and the only
inline JavaScript is an event attribute making a method call, e.g.:
`<body onload=''methodCall('remote-data.xml');''>'

     Currently LibreJS checks for the following licenses:

   * Apache License, Version 2.0
     `http://www.apache.org/licenses/LICENSE-2.0'

   * BSD 2-Clause License
     `http://www.opensource.org/licenses/BSD-2-Clause'

   * BSD 3-Clause License
     `http://www.opensource.org/licenses/BSD-3-Clause'

   * Boost Software License `http://www.boost.org/LICENSE_1_0.txt'

   * Expat License `http://www.jclark.com/xml/copying.txt'

   * GNU Affero General Public License version 3
     `http://www.gnu.org/licenses/agpl.html'

   * GNU All-Permissive License
     `http://www.gnu.org/prep/maintain/html_node/License-Notices-for-Other-Files.html'

   * GNU General Public License version 2
     `http://www.gnu.org/licenses/old-licenses/gpl-2.0.html'

   * GNU General Public License version 3
     `http://www.gnu.org/licenses/gpl.html'

   * Lesser GNU Public License version 2.1
     `http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html'

   * Lesser GNU Public License version 3
     `http://www.gnu.org/licenses/lgpl.html'

   * Mozilla Public License Version 2.0
     `http://www.mozilla.org/MPL/2.0/'

   * CC0 `http://creativecommons.org/publicdomain/zero/1.0/legalcode'

   * X11 License `http://www.xfree86.org/3.3.6/COPYRIGHT2.html#3'

   * ISC License `http://www.isc.org/software/license'


6.2 Undetected Free Licenses
============================

If you are using a free license that isn't detected by LibreJS and isn't
listed in the previous section, please send a message to
<lduros@gnu.org> regarding this license, where code released under this
license can be found, and where to find the license text and
information.

   Many free licenses are listed in this page:
`http://www.gnu.org/licenses/license-list.html'

7 Setting Your JavaScript Free
******************************

_Do you own or maintain a website?_ If so, you can take a stand for
user freedom. All you need to do is to release your JavaScript code
under a free license that will be easily identified by users while
visiting your pages. If you are already using a free library or made a
JavaScript app from scratch, it might only take a few minutes!

   All JavaScript code on a page (inline, on-page, and external) shares
a common scope, and thus is generally either rejected or accepted as a
whole by LibreJS. If some JavaScript code is found to be nontrivial and
nonfree, then most of the time, all the the rest is discarded as well.

   On your website, by taking a look at your HTML source, you can
identify distinct pieces of JavaScript that might be free and some
other that are nonfree.

   Tip: By running LibreJS on your page, you will get a list of all the
JavaScript that was blocked while loading. This can help give you an
overview of the JavaScript in your page.

     Imagine a page that would contain several pieces of JavaScript from
     various sources:

   * On top, within the `<head>' tag, it may have a link to a jQuery
     library file,

   * under, some JavaScript code that you have written,

   * at the bottom a JavaScript-based Facebook widget,

   * and an Analytics tracker.


   * JavaScript that is already free First, you must ensure that the
     library is free. If the file contains a copyright and a license
     notice, you may not need to look further. But if no mention of the
     license is made or if it is too brief, you may have to look for a
     COPYING or LICENSE file within the original library source package
     or on the official website of the library.

   * Your own JavaScript The free license given to your code should be
     compatible with the rest of the JavaScript on a page. A good way
     to check is to read up on them:
     `http://www.gnu.org/licenses/license-list.html'

   * Nonfree JavaScript More likely than not, some of the JavaScript on
     your page will be nonfree. This might be the case with an
     Analytics tracker, social media widgets, and code that runs ads.
     Removing these pieces of code from your site is required in order
     to have the rest accepted as free. There are often alternatives to
     nonfree libraries or to third-party services:

        * If you have used nonfree third-party code as the base to
          write your own code, try to find a free alternative.

        * If you are using a third-party service such as an Analytics
          service, replace it with a free alternative such as Piwik.

        * And if you really cannot find free JavaScript that has already
          been developed, write it yourself! Who knows, your own
          solution might be the start of a brilliant project!


7.1 Adding a stylized comment in your JavaScript files and on your page
=======================================================================

Once you have identified all JavaScript and replaced or removed the
nonfree ones, you can start adding explicit license notices in your
JavaScript files and on your pages. Starting from the external files is
probably easier. You can use long license notices.

   See a "Convention for releasing free JavaScript programs" in the
JavaScript Trap `http://www.gnu.org/philosophy/javascript-trap.html'

   Adding this notice will ensure LibreJS will find the JavaScript file
to be free. The `@licstart' and `@licend' lines at the beginning and
end of the stylized comment are necessary to make a clear statement
that the _entire code_ in the file is free. This means that you must
ensure no nonfree code was carelessly appended at the end of the file.

   For the main HTML page, what the license notice will cover is the
JavaScript contained in all `<script>' with on-page code and the inline

   JavaScript (in event attributes such as onload, onclick, etc, ...).
Since external files have their own stylized comment, they are not
covered by the notice in the main HTML page. Make sure to identify all
the licenses available. LibreJS will only ensure it matches a notice of
an allowed license once, so the order does not matter, but the
responsibility is on you to make sure all code is under the free
licenses mentioned between `@licstart' and `@licend'.

   You should make _only_ one `@licstart' `@licend' comment in your
page, since it pertains to the entire code on page across all
`<script>' tags and inline html attributes.

7.2 JavaScript Web Labels
=========================

You can also choose to publish license information about your external
JavaScript files using the JavaScript Web Labels method. Extensive
information on JavaScript Web Label is detailed at the following URL:
`http://www.gnu.org/licenses/javascript-labels.html'

   The JavaScript Web Labels allow you to easily provide -in the same
time- information for LibreJS and for your users. All it requires is to
create a page listing JavaScript files and the canonical urls of their
free licenses.

Appendix A Installation Requirements
************************************

A.1 Mozilla Browser
===================

You will need one of the many flavors of the Mozilla browser to use
LibreJS. It can be installed on the following:

   GNU IceCat,  Mozilla Firefox, Trisquel Abrowser, Debian Iceweasel.

   While LibreJS works on these browsers starting from version 8, we
recommend you use the latest version of your Mozilla browser. LibreJS
has been tested extensively on multiple GNU/Linux distributions, but it
is also compatible with other operating systems running a version of the
Mozilla browser.

A.2 Mozilla's Add-on SDK
========================

LibreJS uses the Mozilla Add-on SDK (Software Development Kit), a
powerful set of APIs and tools to create add-ons for Mozilla browsers.

   You do not need the Add-on SDK to use LibreJS xpi file or to install
it using the packaged version, but it is required in order to package
the LibreJS source code into an xpi file using `make'. If you would like
to run the tests for LibreJS or make changes to the source files, you
will need the Add-on SDK as well. For the "make" command to work
properly, you must have the `cfx' command available on your system from
the command line.

   The latest tarball for the Add-on SDK is available at:

`https://ftp.mozilla.org/pub/mozilla.org/labs/jetpack/jetpack-sdk-latest.tar.gz'

   Instructions on how to get it working are available here:

`https://addons.mozilla.org/en-US/developers/docs/sdk/latest/dev-guide/tutorials/installation.html'

   In order to use `make' with LibreJS source, however, it is ideal to
have `cfx' available at all times and for all users.

   An easy way to do this is to extract the contents of the tarball and
to place the files inside `/usr/lib/addon-sdk' and then creating a
symbolic link in `/usr/bin', as follows:

     sudo ln -s /usr/lib/addon-sdk/bin/cfx /usr/bin/cfx

   The `cfx' command will then be available to all users.

   The Add-on SDK is released under the Mozilla Public License 2.0.

Appendix B LibreJS Internals
****************************

LibreJS intercepts http responses and rewrites their contents after
analyzing JavaScript within them. It does not remove script nodes and
attributes from the page, but instead "deactivate" them by modifying
the type and src attributes on script elements and by moving the
contents of inline JavaScript attributes such as onClick into harmless
attributes.

   LibreJS detects the most common cases using the http response method
described above, but in extremely rare cases, or when running code
locally, LibreJS cannot detect JavaScript during the response stage.

   To remedy this issue and as a final safeguard, LibreJS takes a look
at the scripts that are about to be executed while the browser engine is
parsing the page. If the script is not found in a list of accepted
scripts populated earlier, the execution will be prevented. This is to
ensure content types that are not regular html (binhex with html in it,
...) and JavaScript do not fall through the cracks and get executed.

Appendix C Tests
****************

In order to better understand how LibreJS works, you can try to visit
these pages with LibreJS installed and enabled and see how they are
being processed:

   *
     `http://lduros.net/assets/librejs/tests/trivial-inline-trivial-external/'
     This page contains trivial on-page JavaScript code, and an external
     script that contains trivial JavaScript code.  Therefore, all
     JavaScript is being executed.

   *
     `http://lduros.net/assets/librejs/tests/trivial-inline-nontrivial-external/'
     The on-page script here is trivial and uses a built-in method, but
     the external script in this page is nontrivial (defines a
     function.)  The external script is blocked, the inline script is
     executed.

   *
     `http://lduros.net/assets/librejs/tests/nontrivial-inline-trivial-external/'
     This page contains nontrivial code on page, and trivial code in its
     external page.  All JavaScript is _removed_ from the page, and the
     external script is never analyzed, since the nontrivial conditions
     are already met in the page.

   * `http://lduros.net/assets/librejs/tests/free-inline-free-external/'
     This page contains free on-page (GPL 3) JavaScript, and free
     external Javascript. Therefore all JavaScript is being executed.

   *
     `http://lduros.net/assets/librejs/tests/free-inline-nonfree-nontrivial-external/'
     This page contains free on-page JavaScript. The external script
     contains nonfree nontrivial JavaScript (AJAX request). The free
     code that is inline is executed, but the external file is blocked.

   * `http://lduros.net/assets/librejs/tests/intrinsec-event/' This page
     contains trivial on-page code, with an intrinsec event in an html
     attribute (onload).  All JavaScript is being executed.

   *
     `http://lduros.net/assets/librejs/tests/trivial-inline-free-external-defines-function/'
     This page contains on-page trivial JavaScript (only makes a window
     alert and loads an external script using the html <script> tag
     with the src attribute. The external script is free (GPL v3), and
     since it is only nontrivial because it defines a function, the
     on-page trivial code is allowed to use it.  All JavaScript is
     being executed.

   *
     `http://lduros.net/assets/librejs/tests/trivial-inline-free-external-writes-script/'
     This page contains trivial on-page JavaScript code, and loads an
     external script that is free. Since no function is defined, the
     external script is being analyzed. The external script is free.
     Trivial here is not allowed because the external script, although
     free, writes a script. The inline trivial script should also have
     a free license notice for it to be interpreted.

   *
     `http://lduros.net/assets/librejs/tests/shelltypist/demo/real-life-example-with-jquery-free.html'
     This is a real-life example of a small jQuery plugin. The on-page
     JavaScript code has a free license. The jQuery external file has a
     free licensed. The shelltypist.js file has a free license as well.
     All licenses are defined between `@licstart' and `@licend'. All
     JavaScript is executed.

   *
     `http://lduros.net/assets/librejs/tests/shelltypist/demo/same-page-without-free-license.html'
     This is the same page than the previous example, except it does
     not have a free license for the main HTML page on-page script.
     While the actual code there is trivial, since jQuery defines
     methods that make use of AJAX, trivial code is not allowed, and no
     JavaScript is executed.

   * `http://lduros.net/assets/librejs/tests/test-labels/' This page
     contains JavaScript (jQuery minified) that does not have proper
     license information in the file, as it has no `@licstart' `@licend'
     comment. It would be considered nonfree, however, the page itself
     uses the JavaScript Web Labels method. On the page itself, you
     will find a link labeled "JavaScript License Information", which
     leads to a page that contains a properly formatted table with the
     required data on the external JavaScript file. LibreJS visits this
     link and determines the version of jQuery linked from the original
     page is the one listed there, and flags it as free. All JavaScript
     is executed (and the title should turn green.)


Appendix D GNU Free Documentation License
*****************************************

                     Version 1.3, 3 November 2008

     Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.
     `http://fsf.org/'

     Everyone is permitted to copy and distribute verbatim copies
     of this license document, but changing it is not allowed.

  0. PREAMBLE

     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.

  1. APPLICABILITY AND DEFINITIONS

     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.

  2. VERBATIM COPYING

     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.

  3. COPYING IN QUANTITY

     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.

  4. MODIFICATIONS

     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:

       A. 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.

       B. 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.

       C. State on the Title page the name of the publisher of the
          Modified Version, as the publisher.

       D. Preserve all the copyright notices of the Document.

       E. Add an appropriate copyright notice for your modifications
          adjacent to the other copyright notices.

       F. 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.

       G. Preserve in that license notice the full lists of Invariant
          Sections and required Cover Texts given in the Document's
          license notice.

       H. Include an unaltered copy of this License.

       I. 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.

       J. 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.

       K. 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.

       L. 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.

       M. Delete any section Entitled "Endorsements".  Such a section
          may not be included in the Modified Version.

       N. Do not retitle any existing section to be Entitled
          "Endorsements" or to conflict in title with any Invariant
          Section.

       O. 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.

  5. COMBINING DOCUMENTS

     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."

  6. COLLECTIONS OF DOCUMENTS

     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.

  7. AGGREGATION WITH INDEPENDENT WORKS

     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.

  8. TRANSLATION

     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.

  9. TERMINATION

     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.

 10. FUTURE REVISIONS OF THIS LICENSE

     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
     `http://www.gnu.org/copyleft/'.

     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.

 11. RELICENSING

     "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.

