The Emacs Widget Library

Copyright © 2000–2013 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.”

Introduction
User Interface
Programming Example
Setting Up the Buffer
Basic Types
Sexp Types
Widget Properties
Defining New Widgets
Widget Browser
Widget Minor Mode
Utilities
Widget Wishlist
GNU Free Documentation License
Index

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1 Introduction

Most graphical user interface toolkits provide a number of standard user interface controls (sometimes known as `widgets' or `gadgets'). Emacs doesn't really support anything like this, except for an incredibly powerful text “widget.” On the other hand, Emacs does provide the necessary primitives to implement many other widgets within a text buffer. The widget package simplifies this task.

The basic widgets are:

link
Areas of text with an associated action. Intended for hypertext links embedded in text.
push-button
Like link, but intended for stand-alone buttons.
editable-field
An editable text field. It can be either variable or fixed length.
menu-choice
Allows the user to choose one of multiple options from a menu, each option is itself a widget. Only the selected option will be visible in the buffer.
radio-button-choice
Allows the user to choose one of multiple options by activating radio buttons. The options are implemented as widgets. All options will be visible in the buffer.
item
A simple constant widget intended to be used in the menu-choice and radio-button-choice widgets.
choice-item
A button item only intended for use in choices. When invoked, the user will be asked to select another option from the choice widget.
toggle
A simple ‘on’/‘off’ switch.
checkbox
A checkbox (‘[ ]’/‘[X]’).
editable-list
Create an editable list. The user can insert or delete items in the list. Each list item is itself a widget.

Now, of what possible use can support for widgets be in a text editor? I'm glad you asked. The answer is that widgets are useful for implementing forms. A form in Emacs is a buffer where the user is supposed to fill out a number of fields, each of which has a specific meaning. The user is not supposed to change or delete any of the text between the fields. Examples of forms in Emacs are the forms package (of course), the customize buffers, the mail and news compose modes, and the HTML form support in the w3 browser.

The advantages for a programmer of using the widget package to implement forms are:

  1. More complex fields than just editable text are supported.
  2. You can give the users immediate feedback if they enter invalid data in a text field, and sometimes prevent entering invalid data.
  3. You can have fixed sized fields, thus allowing multiple fields to be lined up in columns.
  4. It is simple to query or set the value of a field.
  5. Editing happens in the buffer, not in the mini-buffer.
  6. Packages using the library get a uniform look, making them easier for the user to learn.
  7. As support for embedded graphics improve, the widget library will be extended to use the GUI features. This means that your code using the widget library will also use the new graphic features automatically.

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2 User Interface

A form consists of read only text for documentation and some fields, where each field contains two parts, a tag and a value. The tags are used to identify the fields, so the documentation can refer to the ‘foo field’, meaning the field tagged with ‘Foo’. Here is an example form:

     Here is some documentation.
     
     Name: My Name     Choose: This option
     Address:  Some Place
     In some City
     Some country.
     
     See also _other work_ for more information.
     
     Numbers: count to three below
     [INS] [DEL] One
     [INS] [DEL] Eh, two?
     [INS] [DEL] Five!
     [INS]
     
     Select multiple:
     
     [X] This
     [ ] That
     [X] Thus
     
     Select one:
     
     (*) One
     ( ) Another One.
     ( ) A Final One.
     
     [Apply Form] [Reset Form]

The top level widgets in this example are tagged ‘Name’, ‘Choose’, ‘Address’, ‘_other work_’, ‘Numbers’, ‘Select multiple’, ‘Select one’, ‘[Apply Form]’, and ‘[Reset Form]’. There are basically two things the user can do within a form, namely editing the editable text fields and activating the buttons.

2.1 Editable Text Fields

In the example, the value for the ‘Name’ is most likely displayed in an editable text field, and so are values for each of the members of the ‘Numbers’ list. All the normal Emacs editing operations are available for editing these fields. The only restriction is that each change you make must be contained within a single editable text field. For example, capitalizing all text from the middle of one field to the middle of another field is prohibited.

Editable text fields are created by the editable-field widget.

Warning: In an editable-field widget, the editable field must not be adjacent to another widget—that won't work. You must put some text in between. Either make this text part of the editable-field widget itself, or insert it with widget-insert.

The :format keyword is useful for generating the necessary text; for instance, if you give it a value of "Name: %v ", the ‘Name: ’ part will provide the necessary separating text before the field and the trailing space will provide the separating text after the field. If you don't include the :size keyword, the field will extend to the end of the line, and the terminating newline will provide separation after.

Warning: In an editable-field widget, the ‘%v’ escape must be preceded by some other text in the :format string (if specified).

The editing text fields are highlighted with the widget-field-face face, making them easy to find.

— Face: widget-field-face

Face used for other editing fields.

2.2 Buttons

Some portions of the buffer have an associated action, which can be invoked by a standard key or mouse command. These portions are called buttons. The default commands for activating a button are:

<RET>
— Command: widget-button-press pos &optional event

Invoke the button at pos, defaulting to point. If point is not located on a button, invoke the binding in widget-global-map (by default the global map).


Mouse-2
— Command: widget-button-click event

Invoke the button at the location of the mouse pointer. If the mouse pointer is located in an editable text field, invoke the binding in widget-global-map (by default the global map).

There are several different kind of buttons, all of which are present in the example:

The Option Field Tags
When you invoke one of these buttons, you will be asked to choose between a number of different options. This is how you edit an option field. Option fields are created by the menu-choice widget. In the example, ‘Choose’ is an option field tag.
The ‘[INS]’ and ‘[DEL]’ buttons
Activating these will insert or delete elements from an editable list. The list is created by the editable-list widget.
Embedded Buttons
The ‘_other work_’ is an example of an embedded button. Embedded buttons are not associated with any fields, but can serve any purpose, such as implementing hypertext references. They are usually created by the link widget.
The ‘[ ]’ and ‘[X]’ buttons
Activating one of these will convert it to the other. This is useful for implementing multiple-choice fields. You can create them with the checkbox widget.
The ‘( )’ and ‘(*)’ buttons
Only one radio button in a radio-button-choice widget can be selected at any time. When you invoke one of the unselected radio buttons, it will be selected and the previous selected radio button will become unselected.
The ‘[Apply Form]’ and ‘[Reset Form]’ buttons
These are explicit buttons made with the push-button widget. The main difference from the link widget is that the buttons will be displayed as GUI buttons when possible.

To make them easier to locate, buttons are emphasized in the buffer.

— Face: widget-button-face

Face used for buttons.

— User Option: widget-mouse-face

Face used for highlighting a button when the mouse pointer moves across it.

2.3 Navigation

You can use all the normal Emacs commands to move around in a form buffer, plus you will have these additional commands:

<TAB>
— Command: widget-forward &optional count

Move point count buttons or editing fields forward.


M-<TAB>
S-<TAB>
— Command: widget-backward &optional count

Move point count buttons or editing fields backward.

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3 Programming Example

Here is the code to implement the user interface example (see User Interface).

     (require 'widget)
     
     (eval-when-compile
       (require 'wid-edit))
     
     (defvar widget-example-repeat)
     
     (defun widget-example ()
       "Create the widgets from the Widget manual."
       (interactive)
       (switch-to-buffer "*Widget Example*")
       (kill-all-local-variables)
       (make-local-variable 'widget-example-repeat)
       (let ((inhibit-read-only t))
         (erase-buffer))
       (remove-overlays)
       (widget-insert "Here is some documentation.\n\n")
       (widget-create 'editable-field
                      :size 13
                      :format "Name: %v " ; Text after the field!
                      "My Name")
       (widget-create 'menu-choice
                      :tag "Choose"
                      :value "This"
                      :help-echo "Choose me, please!"
                      :notify (lambda (widget &rest ignore)
                                (message "%s is a good choice!"
                                         (widget-value widget)))
                      '(item :tag "This option" :value "This")
                      '(choice-item "That option")
                      '(editable-field :menu-tag "No option" "Thus option"))
       (widget-create 'editable-field
                      :format "Address: %v"
                      "Some Place\nIn some City\nSome country.")
       (widget-insert "\nSee also ")
       (widget-create 'link
                      :notify (lambda (&rest ignore)
                                (widget-value-set widget-example-repeat
                                                  '("En" "To" "Tre"))
                                (widget-setup))
                      "other work")
       (widget-insert
         " for more information.\n\nNumbers: count to three below\n")
       (setq widget-example-repeat
             (widget-create 'editable-list
                            :entry-format "%i %d %v"
                            :notify
                            (lambda (widget &rest ignore)
                              (let ((old (widget-get widget
                                                     ':example-length))
                                    (new (length (widget-value widget))))
                                (unless (eq old new)
                                  (widget-put widget ':example-length new)
                                  (message "You can count to %d." new))))
                            :value '("One" "Eh, two?" "Five!")
                            '(editable-field :value "three")))
       (widget-insert "\n\nSelect multiple:\n\n")
       (widget-create 'checkbox t)
       (widget-insert " This\n")
       (widget-create 'checkbox nil)
       (widget-insert " That\n")
       (widget-create 'checkbox
                      :notify (lambda (&rest ignore) (message "Tickle"))
                      t)
       (widget-insert " Thus\n\nSelect one:\n\n")
       (widget-create 'radio-button-choice
                      :value "One"
                      :notify (lambda (widget &rest ignore)
                                (message "You selected %s"
                                         (widget-value widget)))
                      '(item "One") '(item "Another One.")
                      '(item "A Final One."))
       (widget-insert "\n")
       (widget-create 'push-button
                      :notify (lambda (&rest ignore)
                                (if (= (length
                                        (widget-value widget-example-repeat))
                                       3)
                                    (message "Congratulation!")
                                  (error "Three was the count!")))
                      "Apply Form")
       (widget-insert " ")
       (widget-create 'push-button
                      :notify (lambda (&rest ignore)
                                (widget-example))
                      "Reset Form")
       (widget-insert "\n")
       (use-local-map widget-keymap)
       (widget-setup))

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4 Setting Up the Buffer

Widgets are created with widget-create, which returns a widget object. This object can be queried and manipulated by other widget functions, until it is deleted with widget-delete. After the widgets have been created, widget-setup must be called to enable them.

— Function: widget-create type [ keyword argument ]...

Create and return a widget of type type. The syntax for the type argument is described in Basic Types.

The keyword arguments can be used to overwrite the keyword arguments that are part of type.

— Function: widget-delete widget

Delete widget and remove it from the buffer.

— Function: widget-setup

Set up a buffer to support widgets.

This should be called after creating all the widgets and before allowing the user to edit them.

If you want to insert text outside the widgets in the form, the recommended way to do that is with widget-insert.

— Function: widget-insert

Insert the arguments, either strings or characters, at point. The inserted text will be read-only.

There is a standard widget keymap which you might find useful.

— Const: widget-keymap

<TAB> and C-<TAB> are bound to widget-forward and widget-backward, respectively. <RET> and Mouse-2 are bound to widget-button-press and widget-button-click.

— Variable: widget-global-map

Keymap used by widget-button-press and widget-button-click when not on a button. By default this is global-map.

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5 Basic Types

This is the general syntax of a type specification:

     name ::= (name [keyword argument]... args)
          |   name

Where, name is a widget name, keyword is the name of a property, argument is the value of the property, and args are interpreted in a widget specific way.

The following keyword arguments apply to all widgets:

:value
The initial value for widgets of this type.


:format
This string will be inserted in the buffer when you create a widget. The following ‘%’ escapes are available:
%[
%]
The text inside will be marked as a button.

By default, the text will be shown in widget-button-face, and surrounded by brackets.

— User Option: widget-button-prefix

String to prefix buttons.

— User Option: widget-button-suffix

String to suffix buttons.


%{
%}
The text inside will be displayed with the face specified by :sample-face.
%v
This will be replaced with the buffer representation of the widget's value. What this is depends on the widget type.

Warning: In an editable-field widget, the ‘%v’ escape must be preceded by some other text in the format string (if specified).

%d
Insert the string specified by :doc here.
%h
Like ‘%d’, with the following modifications: If the documentation string is more than one line, it will add a button which will toggle between showing only the first line, and showing the full text. Furthermore, if there is no :doc property in the widget, it will instead examine the :documentation-property property. If it is a lambda expression, it will be called with the widget's value as an argument, and the result will be used as the documentation text.
%t
Insert the string specified by :tag here, or the princ representation of the value if there is no tag.
%%
Insert a literal ‘%’.


:button-face
Face used to highlight text inside %[ %] in the format.


:button-prefix
:button-suffix
Text around %[ %] in the format.

These can be

nil
No text is inserted.
a string
The string is inserted literally.
a symbol
The value of the symbol is expanded according to this table.


:doc
The string inserted by the ‘%d’ escape in the format string.


:tag
The string inserted by the ‘%t’ escape in the format string.


:tag-glyph
Name of image to use instead of the string specified by :tag on Emacsen that supports it.


:help-echo
Specifies how to display a message whenever you move to the widget with either widget-forward or widget-backward or move the mouse over it (using the standard help-echo mechanism). The argument is either a string to display, a function of one argument, the widget, which should return a string to display, or a form that evaluates to such a string.


:follow-link
Specifies how to interpret a <mouse-1> click on the widget. See Defining Clickable Text.


:indent
An integer indicating the absolute number of spaces to indent children of this widget.


:offset
An integer indicating how many extra spaces to add to the widget's grandchildren compared to this widget.


:extra-offset
An integer indicating how many extra spaces to add to the widget's children compared to this widget.


:notify
A function called each time the widget or a nested widget is changed. The function is called with two or three arguments. The first argument is the widget itself, the second argument is the widget that was changed, and the third argument is the event leading to the change, if any.


:menu-tag
Tag used in the menu when the widget is used as an option in a menu-choice widget.


:menu-tag-get
Function used for finding the tag when the widget is used as an option in a menu-choice widget. By default, the tag used will be either the :menu-tag or :tag property if present, or the princ representation of the :value property if not.


:match
Should be a function called with two arguments, the widget and a value, and returning non-nil if the widget can represent the specified value.


:validate
A function which takes a widget as an argument, and returns nil if the widget's current value is valid for the widget. Otherwise it should return the widget containing the invalid data, and set that widget's :error property to a string explaining the error.

The following predefined function can be used:

— Function: widget-children-validate widget

All the :children of widget must be valid.


:tab-order
Specify the order in which widgets are traversed with widget-forward or widget-backward. This is only partially implemented.
  1. Widgets with tabbing order -1 are ignored.
  2. (Unimplemented) When on a widget with tabbing order n, go to the next widget in the buffer with tabbing order n+1 or nil, whichever comes first.
  3. When on a widget with no tabbing order specified, go to the next widget in the buffer with a positive tabbing order, or nil


:parent
The parent of a nested widget (e.g., a menu-choice item or an element of a editable-list widget).


:sibling-args
This keyword is only used for members of a radio-button-choice or checklist. The value should be a list of extra keyword arguments, which will be used when creating the radio-button or checkbox associated with this item.
— User Option: widget-glyph-directory

Directory where glyphs are found. Widget will look here for a file with the same name as specified for the image, with either a .xpm (if supported) or .xbm extension.

— User Option: widget-glyph-enable

If non-nil, allow glyphs to appear on displays where they are supported.

Next: , Up: Basic Types

5.1 The link Widget

Syntax:

     type ::= (link [keyword argument]...  [ value ])

The value, if present, is used to initialize the :value property. The value should be a string, which will be inserted in the buffer.

By default the link will be shown in brackets.

— User Option: widget-link-prefix

String to prefix links.

— User Option: widget-link-suffix

String to suffix links.

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5.2 The url-link Widget

Syntax:

     type ::= (url-link [keyword argument]...  url)

When this link is invoked, the WWW browser specified by browse-url-browser-function will be called with url.

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5.3 The info-link Widget

Syntax:

     type ::= (info-link [keyword argument]...  address)

When this link is invoked, the built-in Info reader is started on address.

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5.4 The push-button Widget

Syntax:

     type ::= (push-button [keyword argument]...  [ value ])

The value, if present, is used to initialize the :value property. The value should be a string, which will be inserted in the buffer.

By default the tag will be shown in brackets.

— User Option: widget-push-button-prefix

String to prefix push buttons.

— User Option: widget-push-button-suffix

String to suffix push buttons.

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5.5 The editable-field Widget

Syntax:

     type ::= (editable-field [keyword argument]... [ value ])

The value, if present, is used to initialize the :value property. The value should be a string, which will be inserted in the field. This widget will match all string values.

The following extra properties are recognized:

:size
The width of the editable field.
By default the field will reach to the end of the line.


:value-face
Face used for highlighting the editable field. Default is widget-field-face, see User Interface.


:secret
Character used to display the value. You can set this to, e.g., ?* if the field contains a password or other secret information. By default, this is nil, and the value is not secret.


:valid-regexp
By default the :validate function will match the content of the field with the value of this attribute. The default value is "" which matches everything.


:keymap
Keymap used in the editable field. The default value is widget-field-keymap, which allows you to use all the normal editing commands, even if the buffer's major mode suppresses some of them. Pressing <RET> invokes the function specified by :action.

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5.6 The text Widget

This is just like editable-field, but intended for multiline text fields. The default :keymap is widget-text-keymap, which does not rebind the <RET> key.

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5.7 The menu-choice Widget

Syntax:

     type ::= (menu-choice [keyword argument]... type ... )

The type argument represents each possible choice. The widget's value will be that of the chosen type argument. This widget will match any value matching at least one of the specified type arguments.

:void
Widget type used as a fallback when the value does not match any of the specified type arguments.


:case-fold
Set this to nil if you don't want to ignore case when prompting for a choice through the minibuffer.


:children
A list whose car is the widget representing the currently chosen type in the buffer.


:choice
The current chosen type.


:args
The list of types.

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5.8 The radio-button-choice Widget

Syntax:

     type ::= (radio-button-choice [keyword argument]...  type ... )

The component types specify the choices, with one radio button for each. The widget's value will be that of the chosen type argument. This widget matches any value that matches at least one of the specified type arguments.

The following extra properties are recognized.

:entry-format
This string will be inserted for each entry in the list. The following ‘%’ escapes are available:
%v
Replace with the buffer representation of the type widget.
%b
Replace with the radio button.
%%
Insert a literal ‘%’.


:button-args
A list of keywords to pass to the radio buttons. Useful for setting, e.g., the ‘:help-echo’ for each button.


:buttons
The widgets representing the radio buttons.


:children
The widgets representing each type.


:choice
The current chosen type


:args
The list of types.

You can add extra radio button items to a radio-button-choice widget after it has been created with the function widget-radio-add-item.

— Function: widget-radio-add-item widget type

Add to radio-button-choice widget widget a new radio button item of type type.

Please note that such items added after the radio-button-choice widget has been created will not be properly destructed when you call widget-delete.

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5.9 The item Widget

Syntax:

     item ::= (item [keyword argument]... value)

The value, if present, is used to initialize the :value property. The value should be a string, which will be inserted in the buffer. This widget will only match the specified value.

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5.10 The choice-item Widget

Syntax:

     item ::= (choice-item [keyword argument]... value)

The value, if present, is used to initialize the :value property. The value should be a string, which will be inserted in the buffer as a button. Activating the button of a choice-item is equivalent to activating the parent widget. This widget will only match the specified value.

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5.11 The toggle Widget

Syntax:

     type ::= (toggle [keyword argument]...)

The widget has two possible states, ‘on’ and ‘off’, which correspond to a t or nil value, respectively.

The following extra properties are recognized:

:on
A string representing the ‘on’ state. By default the string ‘on’.
:off
A string representing the ‘off’ state. By default the string ‘off’.
:on-glyph
Name of a glyph to be used instead of the ‘:on’ text string, on emacsen that supports this.
:off-glyph
Name of a glyph to be used instead of the ‘:off’ text string, on emacsen that supports this.

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5.12 The checkbox Widget

This widget has two possible states, ‘selected’ and ‘unselected’, which corresponds to a t or nil value.

Syntax:

     type ::= (checkbox [keyword argument]...)

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5.13 The checklist Widget

Syntax:

     type ::= (checklist [keyword argument]...  type ... )

The type arguments represent each checklist item. The widget's value will be a list containing the values of all checked type arguments. The checklist widget will match a list whose elements all match at least one of the specified type arguments.

The following extra properties are recognized:

:entry-format
This string will be inserted for each entry in the list. The following ‘%’ escapes are available:
%v
Replaced with the buffer representation of the type widget.
%b
Replace with the checkbox.
%%
Insert a literal ‘%’.


:greedy
Usually a checklist will only match if the items are in the exact sequence given in the specification. By setting :greedy to non-nil, it will allow the items to come in any sequence. However, if you extract the value they will be in the sequence given in the checklist, i.e., the original sequence is forgotten.


:button-args
A list of keywords to pass to the checkboxes. Useful for setting, e.g., the ‘:help-echo’ for each checkbox.


:buttons
The widgets representing the checkboxes.


:children
The widgets representing each type.


:args
The list of types.

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5.14 The editable-list Widget

Syntax:

     type ::= (editable-list [keyword argument]... type)

The value is a list, where each member represents one widget of type type.

The following extra properties are recognized:

:entry-format
This string will be inserted for each entry in the list. The following ‘%’ escapes are available:
%v
This will be replaced with the buffer representation of the type widget.
%i
Insert the [INS] button.
%d
Insert the [DEL] button.
%%
Insert a literal ‘%’.


:insert-button-args
A list of keyword arguments to pass to the insert buttons.


:delete-button-args
A list of keyword arguments to pass to the delete buttons.


:append-button-args
A list of keyword arguments to pass to the trailing insert button.


:buttons
The widgets representing the insert and delete buttons.


:children
The widgets representing the elements of the list.


:args
List whose car is the type of the list elements.

Previous: editable-list, Up: Basic Types

5.15 The group Widget

This widget simply group other widgets together.

Syntax:

     type ::= (group [keyword argument]... type...)

The value is a list, with one member for each type.

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6 Sexp Types

A number of widgets for editing s-expressions (Lisp types), sexp for short, are also available. These basically fall in several categories described in this section.

Next: , Up: Sexp Types

6.1 The Constant Widgets

The const widget can contain any Lisp expression, but the user is prohibited from editing it, which is mainly useful as a component of one of the composite widgets.

The syntax for the const widget is:

     type ::= (const [keyword argument]...  [ value ])

The value, if present, is used to initialize the :value property and can be any s-expression.

— Widget: const

This will display any valid s-expression in an immutable part of the buffer.

There are two variations of the const widget, namely variable-item and function-item. These should contain a symbol with a variable or function binding. The major difference from the const widget is that they will allow the user to see the variable or function documentation for the symbol.

— Widget: variable-item

An immutable symbol that is bound as a variable.

— Widget: function-item

An immutable symbol that is bound as a function.

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6.2 Generic Sexp Widget

The sexp widget can contain any Lisp expression, and allows the user to edit it inline in the buffer.

The syntax for the sexp widget is:

     type ::= (sexp [keyword argument]...  [ value ])
— Widget: sexp

This will allow you to edit any valid s-expression in an editable buffer field.

The sexp widget takes the same keyword arguments as the editable-field widget. See editable-field.

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6.3 Atomic Sexp Widgets

The atoms are s-expressions that do not consist of other s-expressions. For example, a string, a file name, or a symbol are atoms, while a list is a composite type. You can edit the value of an atom with the following widgets.

The syntax for all the atoms are:

     type ::= (construct [keyword argument]...  [ value ])

The value, if present, is used to initialize the :value property and must be an expression of the same type as the widget. That is, the string widget can only be initialized with a string.

All the atom widgets take the same keyword arguments as the editable-field widget. See editable-field.

— Widget: string

Allows you to edit a string in an editable field.

— Widget: regexp

Allows you to edit a regular expression in an editable field.

— Widget: character

Allows you to enter a character in an editable field.

— Widget: file

Allows you to edit a file name in an editable field.

Keywords:

:must-match
If this is set to non-nil, only existing file names will be allowed in the minibuffer.

— Widget: directory

Allows you to edit a directory name in an editable field. Similar to the file widget.

— Widget: symbol

Allows you to edit a Lisp symbol in an editable field.

— Widget: function

Allows you to edit a lambda expression, or a function name with completion.

— Widget: variable

Allows you to edit a variable name, with completion.

— Widget: integer

Allows you to edit an integer in an editable field.

— Widget: number

Allows you to edit a number in an editable field.

— Widget: boolean

Allows you to edit a boolean. In Lisp this means a variable which is either nil meaning false, or non-nil meaning true.

Previous: atoms, Up: Sexp Types

6.4 Composite Sexp Widgets

The syntax for the composite widget construct is:

     type ::= (construct [keyword argument]...  component...)

where each component must be a widget type. Each component widget will be displayed in the buffer, and will be editable by the user.

— Widget: cons

The value of a cons widget must be a cons-cell whose car and cdr have two specified types. It uses this syntax:

          type ::= (cons [keyword argument]...  car-type cdr-type)
— Widget: choice

The value matched by a choice widget must have one of a fixed set of types. The widget's syntax is as follows:

          type ::= (choice [keyword argument]...  type ... )

The value of a choice widget can be anything that matches any of the types.

— Widget: list

The value of a list widget must be a list whose element types match the specified component types:

          type ::= (list [keyword argument]...  component-type...)

Thus, (list string number) matches lists of two elements, the first being a string and the second being a number.

— Widget: vector

The vector widget is like the list widget but matches vectors instead of lists. Thus, (vector string number) matches vectors of two elements, the first being a string and the second being a number.

The above suffice for specifying fixed size lists and vectors. To get variable length lists and vectors, you can use a choice, set, or repeat widget together with the :inline keyword. If any component of a composite widget has the :inline keyword set, its value must be a list which will then be spliced into the composite. For example, to specify a list whose first element must be a file name, and whose remaining elements should either be the symbol t or two strings (file names), you can use the following widget specification:

     (list file
           (choice (const t)
                   (list :inline t
                         :value ("foo" "bar")
                         string string)))

The value of a widget of this type will either have the form (file t) or (file string string).

This concept of :inline may be hard to understand. It was certainly hard to implement, so instead of confusing you more by trying to explain it here, I'll just suggest you meditate over it for a while.

— Widget: set

Specifies a type whose values are the lists whose elements all belong to a given set. The order of elements of the list is not significant. Here's the syntax:

          type ::= (set [keyword argument]...  permitted-element ... )

Use const to specify each permitted element, like this: (set (const a) (const b)).

— Widget: repeat

Specifies a list of any number of elements that fit a certain type.

          type ::= (repeat [keyword argument]...  type)

Next: , Previous: Sexp Types, Up: Top

7 Properties

You can examine or set the value of a widget by using the widget object that was returned by widget-create.

— Function: widget-value widget

Return the current value contained in widget. It is an error to call this function on an uninitialized widget.

— Function: widget-value-set widget value

Set the value contained in widget to value. It is an error to call this function with an invalid value.

Important: You must call widget-setup after modifying the value of a widget before the user is allowed to edit the widget again. It is enough to call widget-setup once if you modify multiple widgets. This is currently only necessary if the widget contains an editing field, but may be necessary for other widgets in the future.

If your application needs to associate some information with the widget objects, for example a reference to the item being edited, it can be done with widget-put and widget-get. The property names must begin with a ‘:’.

— Function: widget-put widget property value

In widget set property to value. property should be a symbol, while value can be anything.

— Function: widget-get widget property

In widget return the value for property. property should be a symbol, the value is what was last set by widget-put for property.

— Function: widget-member widget property

Non-nil if widget has a value (even nil) for property property.

Occasionally it can be useful to know which kind of widget you have, i.e., the name of the widget type you gave when the widget was created.

— Function: widget-type widget

Return the name of widget, a symbol.

Widgets can be in two states: active, which means they are modifiable by the user, or inactive, which means they cannot be modified by the user. You can query or set the state with the following code:

     ;; Examine if widget is active or not.
     (if (widget-apply widget :active)
         (message "Widget is active.")
       (message "Widget is inactive.")
     
     ;; Make widget inactive.
     (widget-apply widget :deactivate)
     
     ;; Make widget active.
     (widget-apply widget :activate)

A widget is inactive if it, or any of its ancestors (found by following the :parent link), have been deactivated. To make sure a widget is really active, you must therefore activate both it and all its ancestors.

     (while widget
       (widget-apply widget :activate)
       (setq widget (widget-get widget :parent)))

You can check if a widget has been made inactive by examining the value of the :inactive keyword. If this is non-nil, the widget itself has been deactivated. This is different from using the :active keyword, in that the latter tells you if the widget or any of its ancestors have been deactivated. Do not attempt to set the :inactive keyword directly. Use the :activate :deactivate keywords instead.

Next: , Previous: Widget Properties, Up: Top

8 Defining New Widgets

You can define specialized widgets with define-widget. It allows you to create a shorthand for more complex widgets, including specifying component widgets and new default values for the keyword arguments.

— Function: define-widget name class doc &rest args

Define a new widget type named name from class.

name and class should both be symbols, class should be one of the existing widget types.

The third argument doc is a documentation string for the widget.

After the new widget has been defined, the following two calls will create identical widgets:

  •                (widget-create name)
    
  •                (apply widget-create class args)
    

Using define-widget just stores the definition of the widget type in the widget-type property of name, which is what widget-create uses.

If you only want to specify defaults for keywords with no complex conversions, you can use identity as your conversion function.

The following additional keyword arguments are useful when defining new widgets:

:convert-widget
Function to convert a widget type before creating a widget of that type. It takes a widget type as an argument, and returns the converted widget type. When a widget is created, this function is called for the widget type and all the widget's parent types, most derived first.

The following predefined functions can be used here:

— Function: widget-types-convert-widget widget

Convert :args as widget types in widget.

— Function: widget-value-convert-widget widget

Initialize :value from :args in widget.


:copy
Function to deep copy a widget type. It takes a shallow copy of the widget type as an argument (made by copy-sequence), and returns a deep copy. The purpose of this is to avoid having different instances of combined widgets share nested attributes.

The following predefined functions can be used here:

— Function: widget-types-copy widget

Copy :args as widget types in widget.


:value-to-internal
Function to convert the value to the internal format. The function takes two arguments, a widget and an external value, and returns the internal value. The function is called on the present :value when the widget is created, and on any value set later with widget-value-set.


:value-to-external
Function to convert the value to the external format. The function takes two arguments, a widget and an internal value, and returns the external value. The function is called on the present :value when the widget is created, and on any value set later with widget-value-set.


:create
Function to create a widget from scratch. The function takes one argument, a widget type, and creates a widget of that type, inserts it in the buffer, and returns a widget object.


:delete
Function to delete a widget. The function takes one argument, a widget, and should remove all traces of the widget from the buffer.

The default value is:

— Function: widget-default-delete widget

Remove widget from the buffer. Delete all :children and :buttons in widget.

In most cases you should not change this value, but instead use :value-delete to make any additional cleanup.


:value-create
Function to expand the ‘%v’ escape in the format string. It will be called with the widget as its argument and should insert a representation of the widget's value in the buffer.

Nested widgets should be listed in :children or :buttons to make sure they are automatically deleted.


:value-delete
Should remove the representation of the widget's value from the buffer. It will be called with the widget as its argument. It doesn't have to remove the text, but it should release markers and delete nested widgets if these are not listed in :children or :buttons.


:value-get
Function to extract the value of a widget, as it is displayed in the buffer.

The following predefined function can be used here:

— Function: widget-value-value-get widget

Return the :value property of widget.


:format-handler
Function to handle unknown ‘%’ escapes in the format string. It will be called with the widget and the character that follows the ‘%’ as arguments. You can set this to allow your widget to handle non-standard escapes.

You should end up calling widget-default-format-handler to handle unknown escape sequences, which will handle the ‘%h’ and any future escape sequences, as well as give an error for unknown escapes.


:action
Function to handle user initiated events. By default, :notify the parent.

The following predefined function can be used here:

— Function: widget-parent-action widget &optional event

Tell :parent of widget to handle the :action. Optional event is the event that triggered the action.


:prompt-value
Function to prompt for a value in the minibuffer. The function should take four arguments, widget, prompt, value, and unbound and should return a value for widget entered by the user. prompt is the prompt to use. value is the default value to use, unless unbound is non-nil, in which case there is no default value. The function should read the value using the method most natural for this widget, and does not have to check that it matches.

If you want to define a new widget from scratch, use the default widget as its base.

— Widget: default

Widget used as a base for other widgets.

It provides most of the functionality that is referred to as “by default” in this text.

Next: , Previous: Defining New Widgets, Up: Top

9 Widget Browser

There is a separate package to browse widgets. This is intended to help programmers who want to examine the content of a widget. The browser shows the value of each keyword, but uses links for certain keywords such as ‘:parent’, which avoids printing cyclic structures.

— Command: widget-browse widget

Create a widget browser for widget. When called interactively, prompt for widget.

— Command: widget-browse-other-window widget

Create a widget browser for widget and show it in another window. When called interactively, prompt for widget.

— Command: widget-browse-at pos

Create a widget browser for the widget at pos. When called interactively, use the position of point.

Next: , Previous: Widget Browser, Up: Top

10 Widget Minor Mode

There is a minor mode for manipulating widgets in major modes that don't provide any support for widgets themselves. This is mostly intended to be useful for programmers doing experiments.

— Command: widget-minor-mode

Toggle minor mode for traversing widgets. With arg, turn widget mode on if and only if arg is positive.

— Variable: widget-minor-mode-keymap

Keymap used in widget-minor-mode.

Next: , Previous: Widget Minor Mode, Up: Top

11 Utilities

— Function: widget-prompt-value widget prompt [ value unbound ]

Prompt for a value matching widget, using prompt. The current value is assumed to be value, unless unbound is non-nil.

— Function: widget-get-sibling widget

Get the item which widget is assumed to toggle. This is only meaningful for radio buttons or checkboxes in a list.

Next: , Previous: Utilities, Up: Top

12 Wishlist

Next: , Previous: Widget Wishlist, Up: Top

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

    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.

  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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Index

This is an alphabetical listing of all concepts, functions, commands, variables, and widgets described in this manual.