This is librejs.info, produced by makeinfo version 6.8 from
librejs.texi.
This manual is for GNU LibreJS (version 7.20, 28 April 2022), a GNU
IceCat extension to detect and block nonfree nontrivial JavaScript on
webpages.
Copyright (C) 2011 2012 2014 2015 Loic J. Duros, 2022 Yuchen Pei
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 no Front-Cover
Texts, and with no Back-Cover Texts. A copy of the license is
included in the section entitled "GNU Free Documentation
License".
INFO-DIR-SECTION GNUzilla
START-INFO-DIR-ENTRY
* LibreJS: (librejs). Detect nonfree nontrivial in GNU Icecat
END-INFO-DIR-ENTRY
File: librejs.info, Node: Top, Next: Overview, Up: (dir)
LibreJS
*******
This manual is for GNU LibreJS (version 7.20, 28 April 2022).
* Menu:
* Overview:: General purpose and information.
* Disclaimer:: Emphasize what LibreJS does and does not.
* Installation:: Installing LibreJS from source.
* How to Use:: How to use LibreJS in IceCat.
* JavaScript Detection:: How LibreJS detects nontrivial Javascript.
* Free Licenses Detection:: List of licenses detected by LibreJS.
* Setting Your JavaScript Free:: Information for website owners/maintainers.
* LibreJS Development Notes:: Documentation about the development of
LibreJS itself.
* Installation Requirements:: Requirements to build and install LibreJS.
* LibreJS Internals:: How LibreJS works under the hood.
* GNU Free Documentation License:: Copying and sharing this documentation.
File: librejs.info, Node: Overview, Next: Disclaimer, Prev: Top, Up: Top
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.
File: librejs.info, Node: Disclaimer, Next: Installation, Prev: Overview, Up: Top
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 <bug-librejs@gnu.org>.
File: librejs.info, Node: Installation, Next: How to Use, Prev: Disclaimer, Up: Top
3 Installation
**************
You can install LibreJS directly using a generated 'librejs.xpi' file,
or by building it from source (*Note LibreJS Development Notes::).
You can also download it from
<https://www.gnu.org/software/librejs/> or
<https://addons.mozilla.org/addon/librejs/>, but due to Mozilla's
review process the download isn't always up to date.
File: librejs.info, Node: How to Use, Next: JavaScript Detection, Prev: Installation, Up: Top
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 top right 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 Script Blacklist/whitelist
==============================
Scripts may be blacklisted or whitelisted through the pop-up menu box.
Whitelisted scripts will always be accepted and blacklisted scripts
will always get rejected.
It is important to note that this feature recognizes which scripts
are blacklisted and whitelisted based on hash. This means that even a
slight difference in a script's code will cause it to be recognized as
a separate script.
Sometimes, JavaScript will be dynamically generated so that it is
different every time a website is loaded. These types of scripts
cannot be whitelisted or blacklisted since they cannot be recognized.
LibreJS has a default whitelist of scripts that are known to be
free but may not declare their license in a format that LibreJS can
understand.
4.3 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 detects contact pages, email addresses that are likely to
be owned by the maintainer of the site, Twitter and identi.ca links,
and phone numbers.
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.
LibreJS includes a default subject line and body for the complaint
email, with a link to the JavaScript Trap essay. This can be
configured in the LibreJS add-on preferences in your web browser.
4.4 Options
===========
You can manage LibreJS's preferences either from the extension's
entry in your browser's Add-ons Manager page ('about:addons') or
by clicking the LibreJS toolbar icon and then the "Settings..."
button on the top right of the popup. This will open a panel
containing a whitelist/blacklist manager and a section to
configure your complaints messages to site owners.
"Whitelist/Blacklist"
LibreJS lets you whitelist or blacklist domain names and
subdomains, to bypass the regular JavaScript checks. This might
be useful, for example, if you are running your own code in a
local web server, or if you don't want to waste computing
resources on script origins you already know you can't trust.
librejs provides a lists manager UI to handle both the lists on
the top of its Options panel.
"Complaint email subject"
Configure the default subject used in complaint emails.
"Complaint email body"
Configure the default body used in complaint emails.
File: librejs.info, Node: JavaScript Detection, Next: Free Licenses Detection, Prev: How to Use, Up: Top
5 JavaScript Detection
**********************
LibreJS considers a very strict subset of JavaScript to be acceptable
for use in non-free scripts. This is meant to maximimize
compatibility with websites that haven't tried to be LibreJS
compatible.
We consider modification of the document non-trivial. There isn't
much that javascript could do that we would consider trivial, for
anything else a free software license would be required.
The criterion is as follows:
For each function definition:
* It must call only primitives.
* The number of conditionals and loops must be at most 3.
* It does not declare an array more than 50 elements long.
* It must not call itself
For the rest of the script, outside of function definitions:
* It must call only primitives and functions defined above in the
page.
* The number of conditionals and loops must be at most 3.
"function" means anything executable that gets a name, including
methods.
Allowed primitives exclude:
* eval()
* ajax
* calling methods with the square bracket notation
* altering the dom
* most other items found as methods of the '.window' object.
File: librejs.info, Node: Free Licenses Detection, Next: Setting Your JavaScript Free, Prev: JavaScript Detection, Up: Top
6 Free Licenses Detection
*************************
The machine readable format for license declarations that LibreJS uses
has changed in the most recent version. This was necessary in order
to not break the asynchronous JS loading model that browsers use.
Scripts are now evaluated independent of eachother and strictly as
they arrive.
File: librejs.info, Node: Setting Your JavaScript Free, Next: LibreJS Development Notes, Prev: Free Licenses Detection, Up: Top
7 Setting Your JavaScript Free
******************************
The first step is releasing your JavaScript under a free license. If
you are already using a free library, or you're not using any
third-party libraries, it might only take a few minutes.
On your website, take a look at your HTML source. You can identify
distinct pieces of JavaScript that might be free and some other that
are 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 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're using a third-party service such as an analytics
service, replace it with a free alternative like Matomo.
* If you can't 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 License tags
================
LibreJS will allow non-trivial scripts to run as long as they use a
free license.
In order for the license of a script to be recognized by LibreJS,
it must be declared using a machine-readable license format.
This format is the same for both remote in-line scripts.
"// @license [magnet link] [identifier]" [Script here] "//
@license-end"
"Identifier" is a name of a license from the following list and the
magnet link in the 'canonicalUrl' field is that license's exact
corresponding magnet link.
{
'AGPL-3.0': {
licenseName: 'GNU AFFERO GENERAL PUBLIC LICENSE version 3',
identifier: 'AGPL-3.0',
canonicalUrl: [
'http://www.gnu.org/licenses/agpl-3.0.html',
'magnet:?xt=urn:btih:0b31508aeb0634b347b8270c7bee4d411b5d4109&dn=agpl-3.0.txt'
],
},
'Apache-2.0': {
licenseName: 'Apache License, Version 2.0',
identifier: 'Apache-2.0',
canonicalUrl: [
'http://www.apache.org/licenses/LICENSE-2.0',
'magnet:?xt=urn:btih:8e4f440f4c65981c5bf93c76d35135ba5064d8b7&dn=apache-2.0.txt'
],
},
'Artistic-2.0': {
licenseName: "Artistic License 2.0",
identifier: 'Artistic-2.0',
canonicalUrl: [
"http://www.perlfoundation.org/artistic_license_2_0",
"magnet:?xt=urn:btih:54fd2283f9dbdf29466d2df1a98bf8f65cafe314&dn=artistic-2.0.txt"
],
},
'BSD-2-Clause': {
licenseName: "BSD 2-Clause License",
identifier: 'BSD-2-Clause',
canonicalUrl: [
'http://www.freebsd.org/copyright/freebsd-license.html',
'magnet:?xt=urn:btih:87f119ba0b429ba17a44b4bffcab33165ebdacc0&dn=freebsd.txt'
],
},
'BSD-3-Clause': {
licenseName: "BSD 3-Clause License",
identifier: 'BSD-3-Clause',
canonicalUrl: [
'http://opensource.org/licenses/BSD-3-Clause',
'magnet:?xt=urn:btih:c80d50af7d3db9be66a4d0a86db0286e4fd33292&dn=bsd-3-clause.txt'
],
},
'BSL-1.0': {
licenseName: 'Boost Software License 1.0',
identifier: 'BSL-1.0',
canonicalUrl: [
'http://www.boost.org/LICENSE_1_0.txt',
'magnet:?xt=urn:btih:89a97c535628232f2f3888c2b7b8ffd4c078cec0&dn=Boost-1.0.txt'
],
},
'CC-BY-1.0': {
licenseName: 'Creative Commons Attribution 1.0 Generic',
identifier: 'CC-BY-1.0',
canonicalUrl: ['https://creativecommons.org/licenses/by/1.0/'],
},
'CC-BY-2.0': {
licenseName: 'Creative Commons Attribution 2.0 Generic',
identifier: 'CC-BY-2.0',
canonicalUrl: ['https://creativecommons.org/licenses/by/2.0/'],
},
'CC-BY-2.5': {
licenseName: 'Creative Commons Attribution 2.5 Generic',
identifier: 'CC-BY-2.5',
canonicalUrl: ['https://creativecommons.org/licenses/by/2.5/'],
},
'CC-BY-3.0': {
licenseName: 'Creative Commons Attribution 3.0 Unported',
identifier: 'CC-BY-3.0',
canonicalUrl: ['https://creativecommons.org/licenses/by/3.0/'],
},
'CC-BY-4.0': {
licenseName: 'Creative Commons Attribution 4.0 International',
identifier: 'CC-BY-4.0',
canonicalUrl: ['https://creativecommons.org/licenses/by/4.0/'],
},
'CC-BY-SA-1.0': {
licenseName: 'Creative Commons Attribution-ShareAlike 1.0 Generic',
identifier: 'CC-BY-SA-1.0',
canonicalUrl: ['https://creativecommons.org/licenses/by-sa/1.0/'],
},
'CC-BY-SA-2.0': {
licenseName: 'Creative Commons Attribution-ShareAlike 2.0 Generic',
identifier: 'CC-BY-SA-2.0',
canonicalUrl: ['https://creativecommons.org/licenses/by-sa/2.0/'],
},
'CC-BY-SA-2.5': {
licenseName: 'Creative Commons Attribution-ShareAlike 2.5 Generic',
identifier: 'CC-BY-SA-2.5',
canonicalUrl: ['https://creativecommons.org/licenses/by-sa/2.5/'],
},
'CC-BY-SA-3.0': {
licenseName: 'Creative Commons Attribution-ShareAlike 3.0 Unported',
identifier: 'CC-BY-SA-3.0',
canonicalUrl: ['https://creativecommons.org/licenses/by-sa/3.0/'],
},
'CC-BY-SA-4.0': {
licenseName: 'Creative Commons Attribution-ShareAlike 4.0 International',
identifier: 'CC-BY-SA-4.0',
canonicalUrl: ['https://creativecommons.org/licenses/by-sa/4.0/'],
},
'CC0-1.0': {
licenseName: 'Creative Commons CC0 1.0 Universal',
identifier: 'CC0-1.0',
canonicalUrl: [
'http://creativecommons.org/publicdomain/zero/1.0/legalcode',
'magnet:?xt=urn:btih:90dc5c0be029de84e523b9b3922520e79e0e6f08&dn=cc0.txt'
],
},
'CPAL-1.0': {
licenseName: 'Common Public Attribution License Version 1.0 (CPAL)',
identifier: 'CPAL-1.0',
canonicalUrl: [
'http://opensource.org/licenses/cpal_1.0',
'magnet:?xt=urn:btih:84143bc45939fc8fa42921d619a95462c2031c5c&dn=cpal-1.0.txt'
],
},
'EPL-1.0': {
licenseName: "Eclipse Public License Version 1.0",
identifier: "EPL-1.0",
canonicalUrl: [
"http://www.eclipse.org/legal/epl-v10.html",
"magnet:?xt=urn:btih:4c6a2ad0018cd461e9b0fc44e1b340d2c1828b22&dn=epl-1.0.txt"
],
},
'Expat': {
licenseName: 'Expat License (sometimes called MIT Licensed)',
identifier: 'Expat',
canonicalUrl: [
'http://www.jclark.com/xml/copying.txt',
'magnet:?xt=urn:btih:d3d9a9a6595521f9666a5e94cc830dab83b65699&dn=expat.txt'
],
},
'FreeBSD': {
licenseName: "FreeBSD License",
identifier: 'FreeBSD',
canonicalUrl: [
'http://www.freebsd.org/copyright/freebsd-license.html',
'magnet:?xt=urn:btih:87f119ba0b429ba17a44b4bffcab33165ebdacc0&dn=freebsd.txt'
],
},
'GNU-All-Permissive': {
licenseName: 'GNU All-Permissive License',
identifier: 'GNU-All-Permissive',
canonicalUrl: [],
},
'GPL-2.0': {
licenseName: 'GNU General Public License (GPL) version 2',
identifier: 'GPL-2.0',
canonicalUrl: [
'http://www.gnu.org/licenses/gpl-2.0.html',
'magnet:?xt=urn:btih:cf05388f2679ee054f2beb29a391d25f4e673ac3&dn=gpl-2.0.txt'
],
},
'GPL-3.0': {
licenseName: 'GNU General Public License (GPL) version 3',
identifier: 'GPL-3.0',
canonicalUrl: [
'http://www.gnu.org/licenses/gpl-3.0.html',
'magnet:?xt=urn:btih:1f739d935676111cfff4b4693e3816e664797050&dn=gpl-3.0.txt'
],
},
'ISC': {
licenseName: "The ISC License",
identifier: 'ISC',
canonicalUrl: [
'https://www.isc.org/downloads/software-support-policy/isc-license/',
'magnet:?xt=urn:btih:b8999bbaf509c08d127678643c515b9ab0836bae&dn=ISC.txt'
],
},
'jQueryTools': {
licenseName: "jQuery Tools",
identifier: 'jQueryTools',
canonicalUrl: [],
},
'LGPL-2.1': {
licenseName: 'GNU Lesser General Public License, version 2.1',
identifier: 'LGPL-2.1',
canonicalUrl: [
'http://www.gnu.org/licenses/lgpl-2.1.html',
'magnet:?xt=urn:btih:5de60da917303dbfad4f93fb1b985ced5a89eac2&dn=lgpl-2.1.txt'
],
},
'LGPL-3.0': {
licenseName: 'GNU Lesser General Public License, version 3',
identifier: 'LGPL-3.0',
canonicalUrl: [
'http://www.gnu.org/licenses/lgpl-3.0.html',
'magnet:?xt=urn:btih:0ef1b8170b3b615170ff270def6427c317705f85&dn=lgpl-3.0.txt'
],
},
'MPL-2.0': {
licenseName: 'Mozilla Public License Version 2.0',
identifier: 'MPL-2.0',
canonicalUrl: [
'http://www.mozilla.org/MPL/2.0',
'magnet:?xt=urn:btih:3877d6d54b3accd4bc32f8a48bf32ebc0901502a&dn=mpl-2.0.txt'
],
},
'PublicDomain': {
licenseName: 'Public Domain',
identifier: 'PublicDomain',
canonicalUrl: [
'magnet:?xt=urn:btih:e95b018ef3580986a04669f1b5879592219e2a7a&dn=public-domain.txt'
],
},
'Unlicense': {
licenseName: 'Unlicense',
identifier: 'Unlicense',
canonicalUrl: [
'http://unlicense.org/UNLICENSE',
'magnet:?xt=urn:btih:5ac446d35272cc2e4e85e4325b146d0b7ca8f50c&dn=unlicense.txt'
],
},
'UPL': {
licenseName: 'Universal Permissive License',
identifier: 'UPL-1.0',
canonicalUrl: [
'https://oss.oracle.com/licenses/upl/',
'magnet:?xt=urn:btih:478974f4d41c3fa84c4befba25f283527fad107d&dn=upl-1.0.txt'
],
},
'WTFPL': {
licenseName: 'Do What The F*ck You Want To Public License (WTFPL)',
identifier: 'WTFPL',
canonicalUrl: [
'http://www.wtfpl.net/txt/copying/',
'magnet:?xt=urn:btih:723febf9f6185544f57f0660a41489c7d6b4931b&dn=wtfpl.txt'
],
},
'X11': {
licenseName: 'X11 License',
identifier: 'X11',
canonicalUrl: [
'magnet:?xt=urn:btih:5305d91886084f776adcf57509a648432709a7c7&dn=x11.txt'
],
},
'XFree86-1.1': {
licenseName: "XFree86 1.1 License",
identifier: 'XFree86-1.1',
canonicalUrl: [
'http://www.xfree86.org/3.3.6/COPYRIGHT2.html#3',
'http://www.xfree86.org/current/LICENSE4.html',
'magnet:?xt=urn:btih:12f2ec9e8de2a3b0002a33d518d6010cc8ab2ae9&dn=xfree86.txt'
],
},
}
7.2 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
<bug-librejs@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>
7.3 Known limitations
=====================
Service workers may cause false positives and false negatives, and
there are multiple ways to disable them. The cleanest way is by
setting 'dom.serviceWorkers.enabled' to 'false' in the 'about:config'
page of your browser.
File: librejs.info, Node: LibreJS Development Notes, Next: Installation Requirements, Prev: Setting Your JavaScript Free, Up: Top
8 LibreJS Development Notes
***************************
8.1 Dependencies
================
LibreJS 7.20 depends on a number of Node.js-based libraries that can
be installed using the 'npm' utility:
$ npm install acorn-loose jassha browserify
$ export PATH=$PATH:./node_modules/.bin
8.2 Building
============
To build the extension run:
$ browserify main_background.js -o bundle.js
To build the extension plus create a .xpi package run:
$ ./build.sh
To build the extension including the automated test suite (see TEST
below) run:
$ ./build.sh -t
or
$ ./build.sh --test
Note: this 'build.sh' script relies on no new source files being
created.
8.3 Debugging
=============
To debug LibreJS, visit the special URL 'about:debugging'. Click on
'Enable add-on debugging' then 'Load Temporary Add-on'. Navigate to
LibreJS's unpacked source directory and select 'manifest.json'.
Lines 39 and 40 in 'main_background.js' assign two variables
controlling the verbosity of 'dbg_print()' statements. Make sure
these are set to false before building a release.
8.4 Testing
===========
An automated test suite runs automatically in its own tab whenever the
extension is loaded as a "Temporary add-on" from 'about:debugging'.
Otherwise (if included in the xpi) it can be launched from the UI by
clicking the "Automated self test..." button.
8.5 Headless testing
====================
To launch the test suite from the command line, ensure the xpi package
has been built with automated test suite. Then install
selenium-webdriver and geckodriver, and ensure the latter is in $PATH:
$ npm install selenium-webdriver geckodriver
$ export PATH=$PATH:./node_modules/.bin
Now you can invoke the test with
$ node ./test.js
which will print out a summary of test results.
Optionally you can also test with a chosen seed
$ node ./test.js 12345
8.6 Headless compliance check
=============================
To check whether a webpage is LibreJS-compliant from the command line,
ensure that the xpi package has been built WITHOUT the automated test
suite. Then install selenium-webdriver and geckodriver, and ensure
the latter is in $PATH:
$ npm install selenium-webdriver
$ npm install geckodriver
$ export PATH=$PATH:./node_modules/.bin
Now you can check a webpage for compliance with
$ node ./compliance.js <url>
It will open the url in a headless browser, save a screenshot, and
output the compliance check result.
For example, to check the compliance of the FSF homepage, do
$ node ./compliance.js https://fsf.org
8.7 Adding new whitelisted libraries
====================================
The script index.js in './hash_script' generates the default
whitelist. Run it with the following command:
'node index.js > output'
Then, just copy the contents of the file "output" to the
appropriate place in main_background.js.
8.8 Releasing a new version
===========================
Update the version number in manifest.json.
Make sure debug statements are set to false on lines 39/40 in
'main_background.js'.
Then run the build script 'build.sh'.
File: librejs.info, Node: Installation Requirements, Next: LibreJS Internals, Prev: LibreJS Development Notes, Up: Top
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.
LibreJS works on these browsers starting from version 60. We
recommend that you use the latest version of your Mozilla browser.
LibreJS has been tested on a GNU/Linux distribution, but it is
compatible any operating system as long as you're using a compatible
Mozilla browser.
File: librejs.info, Node: LibreJS Internals, Next: GNU Free Documentation License, Prev: Installation Requirements, Up: Top
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 "deactivates" them by replacing
their content with a commented notice.
LibreJS detects the most common cases using the HTTP response
method described above, but in less common edge cases, or when running
code locally, LibreJS cannot detect JavaScript during the response
stage.
File: librejs.info, Node: GNU Free Documentation License, Prev: LibreJS Internals, Up: Top
Appendix C 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.
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Node: Setting Your JavaScript Free8904
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