Forms Mode

Forms mode is an Emacs major mode for working with simple textual data bases in a forms-oriented manner. In Forms mode, the information in these files is presented in an Emacs window in a user-defined format, one record at a time. The user can view records or modify their contents.

Forms mode is not a simple major mode, but requires two files to do its job: a control file and a data file. The data file holds the actual data to be presented. The control file describes how to present it.

This file documents Forms mode, a form-editing major mode for GNU Emacs.

Copyright © 1989, 1997, 2001–2013 Free Software Foundation, Inc.

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

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

Forms Example An example: editing the password data base.
Entering and Exiting Forms Mode How to visit a file in Forms mode.
Forms Commands Special commands to use while in Forms mode.
Data File Format How to format the data file.
Control File Format How to control forms mode.
Format Description How to define the forms layout.
Modifying Forms Contents How to modify.
Miscellaneous Forms mode messages and other remarks.
Error Messages List of error messages forms mode can produce.
Long Example A more complex control file example.
Credits Thanks everyone.
GNU Free Documentation License The license for this documentation.
Index Index to this manual.

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1 Forms Example

Let's illustrate Forms mode with an example. Suppose you are looking at the /etc/passwd file, and the screen looks like this:

     ====== /etc/passwd ======
     
     User : root   Uid: 0   Gid: 1
     
     Name : Super User
     
     Home : /
     
     Shell: /bin/sh

As you can see, the familiar fields from the entry for the super user are all there, but instead of being colon-separated on one single line, they make up a forms.

The contents of the forms consist of the contents of the fields of the record (e.g., ‘root’, ‘0’, ‘1’, ‘Super User’) interspersed with normal text (e.g., ‘User : ’, ‘Uid: ’).

If you modify the contents of the fields, Forms mode will analyze your changes and update the file appropriately. You cannot modify the interspersed explanatory text (unless you go to some trouble about it), because that is marked read-only (see Text Properties).

The Forms mode control file specifies the relationship between the format of /etc/passwd and what appears on the screen in Forms mode. See Control File Format.

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2 Entering and Exiting Forms Mode

M-x forms-find-file <RET> control-file <RET>
Visit a database using Forms mode. Specify the name of the control file, not the data file!


M-x forms-find-file-other-window <RET> control-file <RET>
Similar, but displays the file in another window.

The command forms-find-file evaluates the file control-file, and also visits it in Forms mode. What you see in its buffer is not the contents of this file, but rather a single record of the corresponding data file that is visited in its own buffer. So there are two buffers involved in Forms mode: the forms buffer that is initially used to visit the control file and that shows the records being browsed, and the data buffer that holds the data file being visited. The latter buffer is normally not visible.

Initially, the first record is displayed in the forms buffer. The mode line displays the major mode name ‘Forms’, followed by the minor mode ‘View’ if the data base is read-only. The number of the current record (n) and the total number of records in the file(t) are shown in the mode line as ‘n/t’. For example:

     --%%-Emacs: passwd-demo          (Forms View 1/54)----All-------

If the buffer is not read-only, you may change the buffer to modify the fields in the record. When you move to a different record, the contents of the buffer are parsed using the specifications in forms-format-list, and the data file is updated. If the record has fields that aren't included in the display, they are not changed.

Entering Forms mode runs the normal hook forms-mode-hook to perform user-defined customization.

To save any modified data, you can use C-x C-s (forms-save-buffer). This does not save the forms buffer (which would be rather useless), but instead saves the buffer visiting the data file.

To terminate Forms mode, you can use C-x C-s (forms-save-buffer) and then kill the forms buffer. However, the data buffer will still remain. If this is not desired, you have to kill this buffer too.

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3 Forms Commands

The commands of Forms mode belong to the C-c prefix, with one exception: <TAB>, which moves to the next field. Forms mode uses different key maps for normal mode and read-only mode. In read-only Forms mode, you can access most of the commands without the C-c prefix, but you must type ordinary letters instead of control characters; for example, type n instead of C-c C-n.

If your Emacs has been built with X-toolkit support, Forms mode will provide its own menu with a number of Forms mode commands.

C-c C-n
Show the next record (forms-next-record). With a numeric argument n, show the nth next record.


C-c C-p
Show the previous record (forms-prev-record). With a numeric argument n, show the nth previous record.


C-c C-l
Jump to a record by number (forms-jump-record). Specify the record number with a numeric argument.


C-c <
Jump to the first record (forms-first-record).


C-c >
Jump to the last record (forms-last-record). This command also recalculates the number of records in the data file.


<TAB>
C-c <TAB>
Jump to the next field in the current record (forms-next-field). With a numeric argument n, jump forward n fields. If this command would move past the last field, it wraps around to the first field.


C-c C-q
Toggles read-only mode (forms-toggle-read-only). In read-only Forms mode, you cannot edit the fields; most Forms mode commands can be accessed without the prefix C-c if you use the normal letter instead (for example, type n instead of C-c C-n). In edit mode, you can edit the fields and thus change the contents of the data base; you must begin Forms mode commands with C-c. Switching to edit mode is allowed only if you have write access to the data file.


C-c C-o
Create a new record and insert it before the current record (forms-insert-record). It starts out with empty (or default) contents for its fields; you can then edit the fields. With a numeric argument, the new record is created after the current one. See also forms-modified-record-filter in Modifying Forms Contents.


C-c C-k
Delete the current record (forms-delete-record). You are prompted for confirmation before the record is deleted unless a numeric argument has been provided.


C-c C-s regexp <RET>
Search forward for regexp in all records following this one (forms-search-forward). If found, this record is shown. If you give an empty argument, the previous regexp is used again.


C-c C-r regexp <RET>
Search backward for regexp in all records following this one (forms-search-backward). If found, this record is shown. If you give an empty argument, the previous regexp is used again.


M-x forms-prev-field
Similar to forms-next-field but moves backwards.


M-x forms-save-buffer
C-x C-s
Forms mode replacement for save-buffer. When executed in the forms buffer it will save the contents of the (modified) data buffer instead. In Forms mode this function will be bound to C-x C-s.


M-x forms-print
This command can be used to make a formatted print of the contents of the data file.

In addition the command M-x revert-buffer is useful in Forms mode just as in other modes.

The following function key definitions are set up in Forms mode (whether read-only or not):

next
forms-next-record


prior
forms-prev-record


begin
forms-first-record


end
forms-last-record


S-Tab
forms-prev-field

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4 Data File Format

Files for use with Forms mode are very simple—each record (usually one line) forms the contents of one form. Each record consists of a number of fields, which are separated by the value of the string forms-field-sep, which is "\t" (a Tab) by default.

If the format of the data file is not suitable enough you can define the filter functions forms-read-file-filter and forms-write-file-filter. forms-read-file-filter is called when the data file is read from disk into the data buffer. It operates on the data buffer, ignoring read-only protections. When the data file is saved to disk forms-write-file-filter is called to cancel the effects of forms-read-file-filter. After being saved, forms-read-file-filter is called again to prepare the data buffer for further processing.

Fields may contain text which shows up in the forms in multiple lines. These lines are separated in the field using a “pseudo-newline” character which is defined by the value of the string forms-multi-line. Its default value is "\^k" (a Control-K character). If it is set to nil, multiple line fields are prohibited.

If the data file does not exist, it is automatically created.

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5 Control File Format

The Forms mode control file serves two purposes. First, it names the data file to use, and defines its format and properties. Second, the Emacs buffer it occupies is used by Forms mode to display the forms.

The contents of the control file are evaluated as a Lisp program. It should set the following Lisp variables to suitable values:

forms-file
This variable specifies the name of the data file. Example:
          (setq forms-file "my/data-file")

If the control file doesn't set forms-file, Forms mode reports an error.


forms-format-list
This variable describes the way the fields of the record are formatted on the screen. For details, see Format Description.


forms-number-of-fields
This variable holds the number of fields in each record of the data file. Example:
          (setq forms-number-of-fields 10)

If the control file does not set forms-format-list a default format is used. In this situation, Forms mode will deduce the number of fields from the data file providing this file exists and forms-number-of-records has not been set in the control file.

The control file can optionally set the following additional Forms mode variables. Most of them have default values that are good for most applications.

forms-field-sep
This variable may be used to designate the string which separates the fields in the records of the data file. If not set, it defaults to the string "\t" (a Tab character). Example:
          (setq forms-field-sep "\t")


forms-read-only
If the value is non-nil, the data file is treated read-only. (Forms mode also treats the data file as read-only if you don't have access to write it.) Example:
          (set forms-read-only t)


forms-multi-line
This variable specifies the pseudo newline separator that allows multi-line fields. This separator goes between the “lines” within a field—thus, the field doesn't really contain multiple lines, but it appears that way when displayed in Forms mode. If the value is nil, multi-line text fields are prohibited. The pseudo newline must not be a character contained in forms-field-sep.

The default value is "\^k", the character Control-K. Example:

          (setq forms-multi-line "\^k")


forms-read-file-filter
This variable holds the name of a function to be called after the data file has been read in. This can be used to transform the contents of the data file into a format more suitable for forms processing. If it is nil, no function is called. For example, to maintain a gzipped database:
          (defun gzip-read-file-filter ()
            (shell-command-on-region (point-min) (point-max)
                                     "gzip -d" t t))
          (setq forms-read-file-filter 'gzip-read-file-filter)


forms-write-file-filter
This variable holds the name of a function to be called before writing out the contents of the data file. This can be used to undo the effects of forms-read-file-filter. If it is nil, no function is called. Example:
          (defun gzip-write-file-filter ()
            (make-variable-buffer-local 'require-final-newline)
            (setq require-final-newline nil)
            (shell-command-on-region (point-min) (point-max)
                                     "gzip" t t))
          (setq forms-write-file-filter 'gzip-write-file-filter)


forms-new-record-filter
This variable holds a function to be called whenever a new record is created to supply default values for fields. If it is nil, no function is called. See Modifying Forms Contents, for details.


forms-modified-record-filter
This variable holds a function to be called whenever a record is modified, just before updating the Forms data file. If it is nil, no function is called. See Modifying Forms Contents, for details.


forms-insert-after
If this variable is not nil, new records are created after the current record. Also, upon visiting a file, the initial position will be at the last record instead of the first one.


forms-check-number-of-fields
Normally each record is checked to contain the correct number of fields. Under certain circumstances, this can be undesirable. If this variable is set to nil, these checks will be bypassed.

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6 The Format Description

The variable forms-format-list specifies the format of the data in the data file, and how to convert the data for display in Forms mode. Its value must be a list of Forms mode formatting elements, each of which can be a string, a number, a Lisp list, or a Lisp symbol that evaluates to one of those. The formatting elements are processed in the order they appear in the list.

string
A string formatting element is inserted in the forms “as is,” as text that the user cannot alter.
number
A number element selects a field of the record. The contents of this field are inserted in the display at this point. Field numbers count starting from 1 (one).
list
A formatting element that is a list specifies a function call. This function is called every time a record is displayed, and its result, which must be a string, is inserted in the display text. The function should do nothing but returning a string.

The function you call can access the fields of the record as a list in the variable forms-fields.

symbol
A symbol used as a formatting element should evaluate to a string, number, or list; the value is interpreted as a formatting element, as described above.

If a record does not contain the number of fields as specified in forms-number-of-fields, a warning message will be printed. Excess fields are ignored, missing fields are set to empty.

The control file which displays /etc/passwd file as demonstrated in the beginning of this manual might look as follows:

     ;; This demo visits /etc/passwd.
     
     (setq forms-file "/etc/passwd")
     (setq forms-number-of-fields 7)
     (setq forms-read-only t)                 ; to make sure
     (setq forms-field-sep ":")
     ;; Don't allow multi-line fields.
     (setq forms-multi-line nil)
     
     (setq forms-format-list
           (list
            "====== /etc/passwd ======\n\n"
            "User : "    1
            "   Uid: "   3
            "   Gid: "   4
            "\n\n"
            "Name : "    5
            "\n\n"
            "Home : "    6
            "\n\n"
            "Shell: "    7
            "\n"))

When you construct the value of forms-format-list, you should usually either quote the whole value, like this,

     (setq forms-format-list
          '(
            "====== " forms-file " ======\n\n"
            "User : "    1
            (make-string 20 ?-)
            ...
           ))

or quote the elements which are lists, like this:

     (setq forms-format-list
           (list
            "====== " forms-file " ======\n\n"
            "User : "    1
            '(make-string 20 ?-)
            ...
           ))

Forms mode validates the contents of forms-format-list when you visit a database. If there are errors, processing is aborted with an error message which includes a descriptive text. See Error Messages, for a detailed list of error messages.

If no forms-format-list is specified, Forms mode will supply a default format list. This list contains the name of the file being visited, and a simple label for each field indicating the field number.

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7 Modifying The Forms Contents

If forms-read-only is nil, the user can modify the fields and records of the database.

All normal editing commands are available for editing the contents of the displayed record. You cannot delete or modify the fixed, explanatory text that comes from string formatting elements, but you can modify the actual field contents.

If the variable forms-modified-record-filter is non-nil, it is called as a function before the new data is written to the data file. The function receives one argument, a vector that contains the contents of the fields of the record.

The function can refer to fields with aref and modify them with aset. The first field has number 1 (one); thus, element 0 of the vector is not used. The function should return the same vector it was passed; the (possibly modified) contents of the vector determine what is actually written in the file. Here is an example:

     (defun my-modified-record-filter (record)
       ;; Modify second field.
       (aset record 2 (current-time-string))
       ;; Return the field vector.
       record)
     
     (setq forms-modified-record-filter 'my-modified-record-filter)

If the variable forms-new-record-filter is non-nil, its value is a function to be called to fill in default values for the fields of a new record. The function is passed a vector of empty strings, one for each field; it should return the same vector, with the desired field values stored in it. Fields are numbered starting from 1 (one). Example:

     (defun my-new-record-filter (fields)
       (aset fields 5 (login-name))
       (aset fields 1 (current-time-string))
       fields)
     
     (setq forms-new-record-filter 'my-new-record-filter)

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8 Miscellaneous

The global variable forms-version holds the version information of the Forms mode software.

It is very convenient to use symbolic names for the fields in a record. The function forms-enumerate provides an elegant means to define a series of variables whose values are consecutive integers. The function returns the highest number used, so it can be used to set forms-number-of-fields also. For example:

     (setq forms-number-of-fields
           (forms-enumerate
            '(field1 field2 field3 ...)))

This sets field1 to 1, field2 to 2, and so on.

Care has been taken to keep the Forms mode variables buffer-local, so it is possible to visit multiple files in Forms mode simultaneously, even if they have different properties.

If you have visited the control file in normal fashion with find-file or a like command, you can switch to Forms mode with the command M-x forms-mode. If you put ‘-*- forms -*-’ in the first line of the control file, then visiting it enables Forms mode automatically. But this makes it hard to edit the control file itself, so you'd better think twice before using this.

The default format for the data file, using "\t" to separate fields and "\^k" to separate lines within a field, matches the file format of some popular database programs, e.g., FileMaker. So forms-mode can decrease the need to use proprietary software.

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9 Error Messages

This section describes all error messages which can be generated by forms mode. Error messages that result from parsing the control file all start with the text ‘Forms control file error’. Messages generated while analyzing the definition of forms-format-list start with ‘Forms format error’.

Forms control file error: `forms-file' has not been set
The variable forms-file was not set by the control file.
Forms control file error: `forms-number-of-fields' has not been set
The variable forms-number-of-fields was not set by the control file.
Forms control file error: `forms-number-of-fields' must be a number > 0
The variable forms-number-of-fields did not contain a positive number.
Forms control file error: `forms-field-sep' is not a string
Forms control file error: `forms-multi-line' must be nil or a one-character string
The variable forms-multi-line was set to something other than nil or a single-character string.
Forms control file error: `forms-multi-line' is equal to 'forms-field-sep'
The variable forms-multi-line may not be equal to forms-field-sep for this would make it impossible to distinguish fields and the lines in the fields.
Forms control file error: `forms-new-record-filter' is not a function
Forms control file error: `forms-modified-record-filter' is not a function
The variable has been set to something else than a function.
Forms control file error: `forms-format-list' is not a list
The variable forms-format-list was not set to a Lisp list by the control file.
Forms format error: field number xx out of range 1..nn
A field number was supplied in forms-format-list with a value of xx, which was not greater than zero and smaller than or equal to the number of fields in the forms, nn.
Forms format error: fun is not a function
The first element of a list which is an element of forms-format-list was not a valid Lisp function.
Forms format error: invalid element xx
A list element was supplied in forms-format-list which was not a string, number or list.
Warning: this record has xx fields instead of yy
The number of fields in this record in the data file did not match forms-number-of-fields. Missing fields will be made empty.
Multi-line fields in this record - update refused!
The current record contains newline characters, hence can not be written back to the data file, for it would corrupt it. Probably you inserted a newline in a field, while forms-multi-line was nil.
Field separator occurs in record - update refused!
The current record contains the field separator string inside one of the fields. It can not be written back to the data file, for it would corrupt it. Probably you inserted the field separator string in a field.
Record number xx out of range 1..yy
A jump was made to non-existing record xx. yy denotes the number of records in the file.
Stuck at record xx
An internal error prevented a specific record from being retrieved.
No write access to "file"
An attempt was made to enable edit mode on a file that has been write protected.
Search failed: regexp
The regexp could not be found in the data file. Forward searching is done from the current location until the end of the file, then retrying from the beginning of the file until the current location. Backward searching is done from the current location until the beginning of the file, then retrying from the end of the file until the current location.
Wrapped
A search completed successfully after wrapping around.
Warning: number of records changed to nn
Forms mode's idea of the number of records has been adjusted to the number of records actually present in the data file.
Problem saving buffers?
An error occurred while saving the data file buffer. Most likely, Emacs did ask to confirm deleting the buffer because it had been modified, and you said `no'.

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10 Long Example

The following example exploits most of the features of Forms mode. This example is included in the distribution as file etc/forms/forms-d2.el.

     ;; demo2 -- demo forms-mode     -*- emacs-lisp -*-
     
     ;; This sample forms exploit most of the features of forms mode.
     
     ;; Set the name of the data file.
     (setq forms-file
            (expand-file-name "forms/forms-d2.dat" data-directory))
     
     ;; Use forms-enumerate to set field names and number thereof.
     (setq forms-number-of-fields
           (forms-enumerate
            '(arch-newsgroup                 ; 1
              arch-volume                    ; 2
              arch-issue                     ; and ...
              arch-article                   ; ... so
              arch-shortname                 ; ... ... on
              arch-parts
              arch-from
              arch-longname
              arch-keywords
              arch-date
              arch-remarks)))
     
     ;; The following functions are used by this form for layout purposes.
     ;;
     (defun arch-tocol (target &optional fill)
       "Produces a string to skip to column TARGET.
     Prepends newline if needed.
     The optional FILL should be a character, used to fill to the column."
       (if (null fill)
           (setq fill ? ))
       (if (< target (current-column))
           (concat "\n" (make-string target fill))
         (make-string (- target (current-column)) fill)))
     ;;
     (defun arch-rj (target field &optional fill)
       "Produces a string to skip to column TARGET\
      minus the width of field FIELD.
     Prepends newline if needed.
     The optional FILL should be a character,
     used to fill to the column."
       (arch-tocol (- target (length (nth field forms-fields))) fill))
     
     ;; Record filters.
     ;;
     (defun new-record-filter (the-record)
       "Form a new record with some defaults."
       (aset the-record arch-from (user-full-name))
       (aset the-record arch-date (current-time-string))
       the-record)                           ; return it
     (setq forms-new-record-filter 'new-record-filter)
     
     ;; The format list.
     (setq forms-format-list
          (list
            "====== Public Domain Software Archive ======\n\n"
            arch-shortname
            " - "                    arch-longname
            "\n\n"
            "Article: "              arch-newsgroup
            "/"                      arch-article
            " "
            '(arch-tocol 40)
            "Issue: "                arch-issue
            " "
            '(arch-rj 73 10)
            "Date: "                 arch-date
            "\n\n"
            "Submitted by: "         arch-from
            "\n"
            '(arch-tocol 79 ?-)
            "\n"
            "Keywords: "             arch-keywords
            "\n\n"
            "Parts: "                arch-parts
            "\n\n====== Remarks ======\n\n"
            arch-remarks
          ))
     
     ;; That's all, folks!

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11 Credits

Bug fixes and other useful suggestions were supplied by Harald Hanche-Olsen (hanche@imf.unit.no), cwitty@portia.stanford.edu, Jonathan I. Kamens, Per Cederqvist (ceder@signum.se), Michael Lipka (lipka@lip.hanse.de), Andy Piper (ajp@eng.cam.ac.uk), Frederic Pierresteguy (F.Pierresteguy@frcl.bull.fr), Ignatios Souvatzis and Richard Stallman (rms@gnu.org).

This documentation was slightly inspired by the documentation of “rolo mode” by Paul Davis at Schlumberger Cambridge Research (davis%scrsu1%sdr.slb.com@relay.cs.net).

None of this would have been possible without GNU Emacs of the Free Software Foundation. Thanks, Richard!

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Appendix A GNU Free Documentation License

Version 1.3, 3 November 2008
     Copyright © 2000, 2001, 2002, 2007, 2008, 2009 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.
  1. 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.

  2. APPLICABILITY AND DEFINITIONS

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    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.

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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 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.

  3. 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.

  4. 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.

  5. 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:

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

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

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

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

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

  6. 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.”

  7. 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.

  8. 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.

  9. 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.

  10. 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.

  11. 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.

  12. 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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