\input texinfo @c -*- texinfo -*-
@c %**start of header
@setfilename guile-web.info
@settitle Guile Web Programming Library
@setchapternewpage on
@c %**end of header
@ifinfo
This file documents Guile-Web by Clinton Ebadi
Copyright 2003,2004,2005 Clinton Ebadi
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 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.
@end ifinfo
@titlepage
@title Guile-Web: A Web Programming Library
@author Clinton Ebadi
@page
@vskip 0pt plus 1filll
Copyright @copyright{} 2003,2004,2005 Clinton Ebadi
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 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.
@end titlepage
@node Top, Introduction, (dir), (dir)
@comment node-name, next, previous, up
@ifinfo
This document describes Guile-Web by Clinton Ebadi
This document applies to version 0.5.1 of the library named
Guile-Web
Copyright 2003,2004,2005 Clinton Ebadi
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 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.
@end ifinfo
@menu
* Introduction::
* Http Headers::
* hash-dash reader extension::
* Session Management::
* Object Serialization::
* Misc DB Utils::
* XHTML Generation::
* Page Templates::
* GNU Free Documentation License::
@end menu
@node Introduction, Http Headers, Top, Top
@chapter Introduction
Guile-web is a set of modules for Guile Scheme intended to make
programming web applications in Guile easier. Guile-web is not
intended to be used alone; rather as a supplement to guile-www (see
@ref{Top, Guile-WWW Manual, Guile-WWW Manual, guile-www,
Guile-WWW}). Guile-web adds higher level concepts like session
management to Scheme web programming.
@node Http Headers, hash-dash reader extension, Introduction, Top
@chapter Http Header Printing
@code{(web header)} Module
A web application may need to manually output Http Headers. Guile-Web
apps may be running as mod_lisp, fastcgi, or normal clients, and so
must be able to output headers in different formats (e.g. mod_lisp
uses @samp{KEY\nVALUE} instead of @samp{KEY: VALUE}). As such, all
Guile-Web apps should use the @code{(web header)} module for
outputting Http headers.
@defun header:display port name value
This displays the header @var{name} to @var{port} with
@var{value}. This can be overridden by a GOOPS method (indeed this is
what mod_lisp does). The default implementation outputs headers in
standard form @samp{NAME: VALUE\r\n}.
@end defun
@node hash-dash reader extension, Session Management, Http Headers, Top
@chapter Hash-Dash reader extension
@code{(web hash-dash)} Module
Scripts often time need to echo large amounts of static html. Doing
this with Scheme @code{display} is extremely tedious, so guile-web
provides the @code{#-} reader extension to do this. To use it you put
a @code{#-} followed by as many lines of text as you want with a
@code{-#} at the end of the text block. This reader extension will
return the text block as a string. For example:
@example
;;; output page header
(define (header title)
(for-each display
(list
#-
-# title #-
-#))
)
(header "foobar")
@end example
That will create a xhtml 1.0 header.
@node Session Management, Object Serialization, hash-dash reader extension, Top
@chapter Session Management
@code{(web session)} Module
Session Management is a powerful tool that makes web programming much
easier if you are doing authentication. I won't go into the details of
what a session is here, look on Google for that (or send me an email
telling me to put a blurb on it here if you really want it in the
manual). @strong{You must call @code{session:start} before you output
@emph{any} other headers}. You also @emph{must} call
@code{session:save} before you exit your script or else
@strong{@emph{ALL} changes to the session will be @emph{LOST}}.
@itemize @bullet
@item @code{session:start}@*
Call this @emph{before} you make @emph{any} output to start the
session. If a previous session exists for the user, it will be
restored, otherwise a new session is created. This returns @code{#t}
if a new session is successfully created or the old one is restored
and @code{#f} if something fails (e.g. headers have already been
sent).
@item @code{session:save}@*
Call this when you are finished with the session or when you wish to
save the current session data. This will cause the current session
data to be written out to disk. It can possibly be very time consuming
(due to the design of the serializer)
@item @code{session:destroy}@*
Call this when you want to destroy the session (e.g. the user logs
out). All of the variables associated with the current session are
destroyed. This returns @code{#t} if the session is successfuly
destroyed and @code{#f} if something fails (e.g. a session doesn't
currently exist).
@item @code{session:set-save-path! path}@*
This sets the path where session data is saved. The default path is
@file{/tmp/}. If you require secured sessions, you may want to run
your scripts setuid as a special user and create a directory that only
that user can read from to store your session data. This must be
called @emph{before} @code{session:start}.
@item @code{session:set-cookie-name! name}@*
This sets the name of the cookie sent to the user to manage their
session. You should only have to change this if you want to use more
than one session cookie for a domain (e.g. you have multiple users
using your domain for hosting). Of course, it is probably good to just
set this to a more descriptive name than the default libcgi name
anyway.
@emph{before} @code{session:start}.
@item @code{session:register-var name value}@*
This registers @code{name} (which must be a symbol)
with the current session and sets it's value to
@code{value}. @code{value} is serialized using @code{serialize} from
the object serialization module, @xref{Object Serialization, Object
Serialization}. Not all data types can be serialized; if a type is not
supported you will have to write a serializer and deserializer for
it. This returns @code{#t} if @code{name} is succesfully registered
and @code{#f} on failure (e.g. @code{name} has already been
registered).
@item @code{session:unregister-var name}@*
This unregisters the session variable @code{name}. Returns @code{#t}
if @code{name} is succesfully unregistered; @code{#f} otherwise
(e.g. @code{name} is not a valid session variable).
@item @code{session:alter-var! name new-value}@*
The session variable @code{name} is set to @code{new-value}. This
return @code{#t} if @code{name} is succesfully set to
@code{new-value}.
@item @code{session:get-value name}@*
This gets and returns the value of the session variable
@code{name}. This returns the value of @code{name} on success and
@code{""} on failure.
@item @code{session:var-exists? name}@*
This checks if the session variable @code{name} exists. If it does,
@code{#t} is returned; otherwise @code{#f} is returned.
@end itemize
An easy way to to ensure that the session is saved if you are using
scripts that execute and exit is to add @code{session:save} to the
@code{exit-hook} hook.
@example
(add-hook! exit-hook session:save)
@end example
@node Object Serialization, Misc DB Utils, Session Management, Top
@chapter Object Serialization
@code{(web serialize)} Module
When you serialize an object you transform the object into a
representation suitable for storing in a file (usually). The serialize
module exports several functions for serializing and unserializing
GOOPS objects. Note that every SMOB has a GOOPS class associated with
it once GOOPS is loaded (?).
Note that this module is really meant for internal usage by the
session mananger, but since you have to add your own serializers for
user defined types, I figured I may as well may the entire API public
(someone might find it useful).
@itemize @bullet
@item Generic @code{%serialize (item ) serial-table}@*
You should write a version of @code{%serialize} for every type you want
to serialize, except for the built in types which already have
serializers or any GOOPS class. Simply @code{(define-method (%serialize
(item )))} to create your new serializer. The serialize must
produce a dotted pair in the form @code{(type . value)}. E.g. a
@code{} is serialized as @code{(
. value)}. @code{type} is the @emph{symbolic representation} of the
type. @code{%serialize} must return the serialized object as an sobject
to the caller. This can be done by using @code{object->sobject}
(e.g. @code{(object->sobject (cons 'type value))}). Note that the
default GOOPS %serialize method may not do what you want it too. You
can customize your object serialization like you would with any part
of the standard GOOPS MOP. @code{serial-table} is used interally by
other procedures that you may have to use.
@item @code{@@serialize item serial-table}@*
If your object is a container object, you @emph{must} call
@code{@@serialize} on the items contained within your container. Simple
call @code{@@serialize} on each item, passing along the
@code{serial-table} given to @code{%serialize}.
@item @code{unserialize}@*
This will unserialize the serialized object @code{serialized-data} and
return it.
@item @code{add-unserializer type unserializer}@*
This adds an unserialize for @code{type}. The function
@code{unserializer} takes two arguments which are the @code{value}
member of the serialized data and the @code{serial-table}. E.g. take
the serialized data @code{"( . 45)"}; @code{unserializer} will
be passed @code{45} and a hash table containing partially unserialized
data as its argument. @code{unserializer} must return the unserialized
object.
@item @code{@@unserialize item serial-table}@*
If your object is a container, just as you called @code{@@serialize} on
each member of the container during serialization, you must call
@code{@@unserialize} on each item.
@end itemize
@node Misc DB Utils, XHTML Generation, Object Serialization, Top
@chapter Miscellaneous Database Tools
@code{(web db)} Module
These are only useful if you are using SimpleSQL, available from
@url{http://guile-simplesql.sourceforge.net/}. (Maybe this module will
be merged into it). The problem with simplesql is that it returns a
list of vectors that is very difficult to use. This module defines a
set of procedures that converts the result of a @code{simplesql-query}
into a much nicer form. We will call this data type an @dfn{assoc}.
@itemize @bullet
@item @code{db:res->assoc result}@*
This converts the result of a @code{simplesql-query} into the form
used by the module. This returns the new assoc.
@item @code{db:numrows? assoc}@*
This returns the number of rows in assoc.
@item @code{db:fetch-row assoc row-num}@*
This fetches the hash table at @code{row-num} in @code{assoc}.
@item @code{db:get hash-table key}@*
This returns the data associated with the key @code{key} in the hash
table @code{hash-table}. @code{key} is a symbol that is the name of
the row in the query (e.g. the row named @code{"foo"} becomes the key
@code{'foo}).
@end itemize
If you would like to iterate over the result you can use
@code{array-for-each} and @code{array-map} (or any of the other array
functions) because a vector is simply an array of rank 1. I decided to
use a vector instead of a list for this because it is more
efficient for this (e.g. the result is constant, the number of rows
may be very large and accessing a large numbered row is constant time
for the vector and O(N) time for a list, etc.).
@node XHTML Generation, Page Templates, Misc DB Utils, Top
@chapter XHtml Generation
@code{(web xhtml)} Module
Being able to generate correct HTML is a useful thing, so I have
written a set of procedures for generating xhtml 1.0 documents. Note
that correctness isn't entirely forced; you can, for example, put an
inline element in a place where only a block level element is valid;
but it does make generating a xhtml document somewhat easier.
There are two ways to use the html module: with the global instance or
by specifying your own instance. If you use your own object, you must
@code{make} a @code{}, which takes these keyword arguments:
@itemize @bullet
@item @code{#:port} The port to display output to
@item @code{#:attributes} Default attribute values for all tags
@end itemize
@code{#:attributes} is a list of lists that specify the default values
for all tag attributes, e.g. @code{((style "special style") (class
"magic"))}.
@itemize @bullet
@item @code{xhtml:print <@var{document}> @var{expression} ...}
@end itemize
To display data generated by the various tag procedures, you use
@code{xhtml:print}. If the first argument is a @code{} all
of the tags will output using the default port for that object and use
the default attribute values for that object as well. If the first
argument is not a @code{}, then the expressions will be
printed to the output port of the global @code{} which is
the @code{(current-output-port)} of the dynamic root you are in (there
is also one global @code{} per dynamic root).
@itemize @bullet
@item @code{xhtml:tags @var{tags} ...}
If you need to use more than one tag where normally only one can be
used, simply pass them all to xhtml:tags. This is useful if you wish
to @code{xhtml:print} multiple tags which are on the same level in the
document heirarchy as the others.
@end itemize
@itemize @bullet
@item @code{xhtml:@var{tagname} <#:atts attributes> }
@item @code{xhtml:@var{tagname}-start <#:atts attributes>}
@item @code{xhtml:@var{tagname}-end}
@end itemize
All tags have a producedure named @code{xhtml:@var{tagname}}. If the tag
is non-empty, this may tag any number of forms to be printed inside of
the tag as arguments, including other tags. Also is the tag is
non-empty, there are -start and -end procedures defined to spit out the
start and end tags of the tag. If a tag is empty, it may not contain any
other data. All tags take an optinal @code{#:atts} keyword argument that
contains a list of lists that specify the attributes for the tag in the
form @code{((attribute-name-as-a-symbol "attribute value in a string")
...)}. The start tag also supports this, the end tag doesn't. You must
print the output of all the tag function with @code{xhtml:print}.
All documents should begin with a call to @code{xhtml:dtd} which returns
the DTD for the document. Its @code{#:atts} argument takes one member:
@code{encoding} which is the encoding of the document. This defaults to
@code{"iso-8859-1"}.
Available tags:
@include xhtmldoc.texinfo
An example:
@example
(use-modules (web html)
(web hash-dash))
(display "Content-Type: text/html\r\n\r\n")
(force-output (current-output-port))
(xhtml:print
(xhtml:dtd
(xhtml:html-start)))
(xhtml:print
(xhtml:head
(xhtml:title "MOO")))
(xhtml:print
(xhtml:body-start)
(xhtml:h1 "tra la la!")
(xhtml:p
#- Moo moo moooooooooo. I am so cool.
Multiple lines are so great.
All will fear my elite! -#
(xhtml:br)
#- This is where the second line begins. -#)
(xhtml:body-end)
(xhtml:html-end))
@end example
There is another procedure, @code{xhtml:tag-tree->shtml @var{tag}}
which accepts a tag as its argument and return the tag tree in shtml
(a subset of SXML used by HtmlPrag).
@node Page Templates, GNU Free Documentation License, XHTML Generation, Top
@chapter Page Templates
@code{(web template)} Module
Languages like PHP allow one to embed code within a document. The
solution used by PHP isn't really optimal; guile-web uses a slightly
better method of page templates. A page template is just a document
with a bit of special formatting to make calls to various template
procedures. This is somewhat similar to Perl's Mason module but is
currently much more limited.
Scheme procedures:
@itemize
@item @code{template:parse @var{command-table} @var{port}}, reads from
@var{port} and looks for template procedure calls. Procedures are
supplied in @var{command-table} which is a hash table of symbol and
procedure pairs. @code{template:parse} returns a list of strings that
represent non-template portions of the port along with any data
returned by template calls. The list can then be processed however one
chooses (e.g. a simple parse-and-display script could @code{(for-each
display (template:parse ...))}). This will call @code{template:error}
when an error occurs.
@item @code{template:error @var{fmt} . @var{args}}, Whenever an error
occurs, @code{template:parse} calls this procedure with a format
string (@var{fmt}) usable by @code{simple-format} along with the
@var{args} to @code{simple-format}. Anything returned by this
procedure will end up in the list returned by
@code{template:parse}. By default this throws an error with the key
@code{'web:format:error}.
@item @code{template:set-error-handler @var{error-handler}}, use this
to override the default @code{template:error} procedure. This returns
the current error handling procedure.
@end itemize
To make a template call from a template, you encase the call in square
brackets ([ and ]). The call is merely a procedure call that is
expected to return some data that is substituted into the page at that
point. If a double [[ is found it will be inserted into the output
stream as a single [; a double ]] can be used inside of a template
call to pass a literal ] to the procedure.
An example script that parses a page:
@example
;;; page.scm
(use-modules (web template))
(let
(
;; open template
(my-file (open-input-file "page.tmpl"))
;; Create a command table
(my-procs (make-hash-table 10))
;; Output port
(page-out (open-output-file "page.out")))
;; Initialize command table
(hash-set! my-procs 'comment
(lambda args ""))
(hash-set! my-procs 'cool
(lambda (who)
(string-append who "is cool")))
(hash-set! my-procs 'add +)
;; Parse page and write it to page.out
(for-each (lambda (x) (display x page-out))
(template:parse my-procs my-file))
(close-port page-out))
@end example
The page used by the script:
@example
[comment page.tmpl]
Tra la la!
[[This will be inside of square brackets]
2 + 2 = [add 2 2]. I think that [cool Clinton]! He has a Camaro and
wrote Guile-Web so he deserves mad props.
Only he's not a hip-hop kid so he doesn't think that 2 + 2 = [add 2 3]
or anything. Yeah. Also, this example really isn't that great.
[comment Since comment is a multi-argument procedure, I can put
whatever I want in here as long as it is a valid piece of Scheme data.]
@end example
@node GNU Free Documentation License, , Page Templates, Top
@appendix GNU Free Documentation License
@cindex FDL, GNU Free Documentation License
@center Version 1.2, November 2002
@display
Copyright @copyright{} 2000,2001,2002 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA 02111-1307, USA
Everyone is permitted to copy and distribute verbatim copies
of this license document, but changing it is not allowed.
@end display
@enumerate 0
@item
PREAMBLE
The purpose of this License is to make a manual, textbook, or other
functional and useful document @dfn{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.
@item
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
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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
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The ``Invariant Sections'' are certain Secondary Sections whose titles
are designated, as being those of Invariant Sections, in the notice
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Invariant Sections. If the Document does not identify any Invariant
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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
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A ``Transparent'' copy of the Document means a machine-readable copy,
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An image format is not Transparent if used for any substantial amount
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Examples of suitable formats for Transparent copies include plain
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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.
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.
@item
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.
@item
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.
@item
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:
@enumerate A
@item
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.
@item
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.
@item
State on the Title page the name of the publisher of the
Modified Version, as the publisher.
@item
Preserve all the copyright notices of the Document.
@item
Add an appropriate copyright notice for your modifications
adjacent to the other copyright notices.
@item
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.
@item
Preserve in that license notice the full lists of Invariant Sections
and required Cover Texts given in the Document's license notice.
@item
Include an unaltered copy of this License.
@item
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.
@item
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.
@item
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.
@item
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.
@item
Delete any section Entitled ``Endorsements''. Such a section
may not be included in the Modified Version.
@item
Do not retitle any existing section to be Entitled ``Endorsements'' or
to conflict in title with any Invariant Section.
@item
Preserve any Warranty Disclaimers.
@end enumerate
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.
@item
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.''
@item
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.
@item
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.
@item
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.
@item
TERMINATION
You may not copy, modify, sublicense, or distribute the Document except
as expressly provided for under this License. Any other attempt to
copy, modify, sublicense or distribute the Document is void, and will
automatically terminate your rights under this License. However,
parties who have received copies, or rights, from you under this
License will not have their licenses terminated so long as such
parties remain in full compliance.
@item
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
@uref{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.
@end enumerate
@page
@appendixsubsec 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:
@smallexample
@group
Copyright (C) @var{year} @var{your name}.
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.2
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''.
@end group
@end smallexample
If you have Invariant Sections, Front-Cover Texts and Back-Cover Texts,
replace the ``with...Texts.'' line with this:
@smallexample
@group
with the Invariant Sections being @var{list their titles}, with
the Front-Cover Texts being @var{list}, and with the Back-Cover Texts
being @var{list}.
@end group
@end smallexample
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.
@bye