emacs/doc/misc/widget.texi

\input texinfo.tex
@c %**start of header
@setfilename ../../info/widget.info
@settitle The Emacs Widget Library
@include docstyle.texi
@syncodeindex fn cp
@syncodeindex vr cp
@syncodeindex ky cp
@c %**end of header

@copying
Copyright @copyright{} 2000--2020 Free Software Foundation, Inc.

@quotation
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.''
@end quotation
@end copying

@dircategory Emacs lisp libraries
@direntry
* Widget: (widget).             The "widget" package used by the Emacs
                                  Customization facility.
@end direntry


@titlepage
@title The Emacs Widget Library
@page
@vskip 0pt plus 1filll
@insertcopying
@end titlepage

@contents

@node Top
@top The Emacs Widget Library

@insertcopying

@menu
* 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::
@end menu

@node  Introduction
@chapter 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 @code{widget} package simplifies this task.

@cindex basic widgets
@cindex widgets, basic types
The basic widgets are:

@table @code
@item link
Areas of text with an associated action.  Intended for hypertext links
embedded in text.
@item push-button
Like link, but intended for stand-alone buttons.
@item editable-field
An editable text field.  It can be either variable or fixed length.
@item 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.
@item 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 item
A simple constant widget intended to be used in the @code{menu-choice} and
@code{radio-button-choice} widgets.
@item 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.
@item toggle
A simple @samp{on}/@samp{off} switch.
@item checkbox
A checkbox (@samp{[ ]}/@samp{[X]}).
@item editable-list
Create an editable list.  The user can insert or delete items in the
list.  Each list item is itself a widget.
@end table

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 @dfn{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 @file{forms}
package (of course), the customize buffers, the mail and news compose
modes, and the @acronym{HTML} form support in the @file{w3} browser.

@cindex widget library, why use it
The advantages for a programmer of using the @code{widget} package to
implement forms are:

@enumerate
@item
More complex fields than just editable text are supported.
@item
You can give the users immediate feedback if they enter invalid data in a
text field, and sometimes prevent entering invalid data.
@item
You can have fixed sized fields, thus allowing multiple fields to be
lined up in columns.
@item
It is simple to query or set the value of a field.
@item
Editing happens in the buffer, not in the mini-buffer.
@item
Packages using the library get a uniform look, making them easier for
the user to learn.
@item
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.
@end enumerate

@node User Interface
@chapter 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
@samp{foo field}, meaning the field tagged with @samp{Foo}. Here is an
example form:

@example
Here is some documentation.

Name: @i{My Name}     @strong{Choose}: This option
Address:  @i{Some Place
In some City
Some country.}

See also @b{_other work_} for more information.

Numbers: count to three below
@b{[INS]} @b{[DEL]} @i{One}
@b{[INS]} @b{[DEL]} @i{Eh, two?}
@b{[INS]} @b{[DEL]} @i{Five!}
@b{[INS]}

Select multiple:

@b{[X]} This
@b{[ ]} That
@b{[X]} Thus

Select one:

@b{(*)} One
@b{( )} Another One.
@b{( )} A Final One.

@b{[Apply Form]} @b{[Reset Form]}
@end example

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

@section Editable Text Fields

In the example, the value for the @samp{Name} is most likely displayed
in an editable text field, and so are values for each of the members of
the @samp{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 @code{editable-field} widget.

@strong{Warning:} In an @code{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 @code{editable-field} widget itself, or insert it with
@code{widget-insert}.

The @code{:format} keyword is useful for generating the necessary
text; for instance, if you give it a value of @code{"Name: %v "},
the @samp{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
@code{:size} keyword, the field will extend to the end of the
line, and the terminating newline will provide separation after.

@strong{Warning:} In an @code{editable-field} widget, the @samp{%v} escape
must be preceded by some other text in the @code{:format} string
(if specified).

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

@deffn Face widget-field-face
Face used for other editing fields.
@end deffn

@section Buttons

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

@table @kbd
@item @key{RET}
@deffn Command widget-button-press @var{pos} &optional @var{event}
Invoke the button at @var{pos}, defaulting to point.
If point is not located on a button, invoke the binding in
@code{widget-global-map} (by default the global map).
@end deffn

@kindex mouse-2 @r{(on button widgets})
@item mouse-2
@deffn Command widget-button-click @var{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
@code{widget-global-map} (by default the global map).
@end deffn
@end table

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

@table @emph
@cindex option field tag
@item 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 @code{menu-choice} widget.  In
the example, @samp{@b{Choose}} is an option field tag.
@item The @samp{@b{[INS]}} and @samp{@b{[DEL]}} buttons
Activating these will insert or delete elements from an editable list.
The list is created by the @code{editable-list} widget.
@cindex embedded buttons
@item Embedded Buttons
The @samp{@b{_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 @code{link} widget.
@item The @samp{@b{[ ]}} and @samp{@b{[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
@code{checkbox} widget.
@item The @samp{@b{( )}} and @samp{@b{(*)}} buttons
Only one radio button in a @code{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.
@item The @samp{@b{[Apply Form]}} and @samp{@b{[Reset Form]}} buttons
These are explicit buttons made with the @code{push-button} widget.  The
main difference from the @code{link} widget is that the buttons will be
displayed as GUI buttons when possible.
@end table

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

@deffn Face widget-button-face
Face used for buttons.
@end deffn

@defopt widget-mouse-face
Face used for highlighting a button when the mouse pointer moves across
it.
@end defopt

@section Navigation

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

@table @kbd
@item @key{TAB}
@deffn Command widget-forward &optional count
Move point @var{count} buttons or editing fields forward.
@end deffn
@item @kbd{M-@key{TAB}}
@itemx @kbd{S-@key{TAB}}
@deffn Command widget-backward &optional count
Move point @var{count} buttons or editing fields backward.
@end deffn
@end table

@node Programming Example
@chapter Programming Example

@cindex widgets, programming example
@cindex example of using widgets
Here is the code to implement the user interface example (@pxref{User
Interface}).

@lisp
(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))
@end lisp

@node Setting Up the Buffer
@chapter Setting Up the Buffer

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

@defun widget-create type [ keyword argument ]@dots{}
Create and return a widget of type @var{type}.
The syntax for the @var{type} argument is described in @ref{Basic Types}.

The keyword arguments can be used to overwrite the keyword arguments
that are part of @var{type}.
@end defun

@defun widget-delete widget
Delete @var{widget} and remove it from the buffer.
@end defun

@defun 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.
@end defun

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

@defun widget-insert
Insert the arguments, either strings or characters, at point.
The inserted text will be read-only.
@end defun

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

@findex widget-button-press
@findex widget-button-click
@defvr Const widget-keymap
@key{TAB} and @kbd{C-@key{TAB}} are bound to @code{widget-forward} and
@code{widget-backward}, respectively.  @key{RET} and @kbd{mouse-2}
are bound to @code{widget-button-press} and
@code{widget-button-click}.
@end defvr

@defvar widget-global-map
Keymap used by @code{widget-button-press} and @code{widget-button-click}
when not on a button.  By default this is @code{global-map}.
@end defvar

@node Basic Types
@chapter Basic Types

This is the general syntax of a type specification:

@example
@var{name} ::= (@var{name} [@var{keyword} @var{argument}]... @var{args})
     |   @var{name}
@end example

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

@cindex keyword arguments
The following keyword arguments apply to all widgets:

@table @code
@vindex value@r{ keyword}
@item :value
The initial value for widgets of this type.

@vindex format@r{ keyword}
@item :format
This string will be inserted in the buffer when you create a widget.
The following @samp{%} escapes are available:

@table @samp
@item %[
@itemx %]
The text inside will be marked as a button.

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

@defopt widget-button-prefix
String to prefix buttons.
@end defopt

@defopt widget-button-suffix
String to suffix buttons.
@end defopt

@item %@{
@itemx %@}
The text inside will be displayed with the face specified by
@code{:sample-face}.

@item %v
This will be replaced with the buffer representation of the widget's
value.  What this is depends on the widget type.

@strong{Warning:} In an @code{editable-field} widget, the @samp{%v} escape
must be preceded by some other text in the format string (if specified).

@item %d
Insert the string specified by @code{:doc} here.

@item %h
Like @samp{%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 @code{:doc} property in the widget, it will
instead examine the @code{: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.

@item %t
Insert the string specified by @code{:tag} here, or the @code{princ}
representation of the value if there is no tag.

@item %%
Insert a literal @samp{%}.
@end table

@vindex button-face@r{ keyword}
@item :button-face
Face used to highlight text inside %[ %] in the format.

@vindex button-prefix@r{ keyword}
@vindex button-suffix@r{ keyword}
@item :button-prefix
@itemx :button-suffix
Text around %[ %] in the format.

These can be
@table @emph
@item nil
No text is inserted.

@item a string
The string is inserted literally.

@item a symbol
The value of the symbol is expanded according to this table.
@end table

@vindex doc@r{ keyword}
@item :doc
The string inserted by the @samp{%d} escape in the format
string.

@vindex tag@r{ keyword}
@item :tag
The string inserted by the @samp{%t} escape in the format
string.

@vindex tag-glyph@r{ keyword}
@item :tag-glyph
Name of image to use instead of the string specified by @code{:tag} on
Emacsen that supports it.

@vindex help-echo@r{ keyword}
@item :help-echo
Specifies how to display a message whenever you move to the widget with
either @code{widget-forward} or @code{widget-backward} or move the mouse
over it (using the standard @code{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.

@vindex follow-link@r{ keyword}
@item :follow-link
Specifies how to interpret a @key{mouse-1} click on the widget.
@xref{Clickable Text,, Defining Clickable Text, elisp, the Emacs Lisp Reference Manual}.

@vindex indent@r{ keyword}
@item :indent
An integer indicating the absolute number of spaces to indent children
of this widget.

@vindex offset@r{ keyword}
@item :offset
An integer indicating how many extra spaces to add to the widget's
grandchildren compared to this widget.

@vindex extra-offset@r{ keyword}
@item :extra-offset
An integer indicating how many extra spaces to add to the widget's
children compared to this widget.

@vindex notify@r{ keyword}
@item :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.

@vindex menu-tag@r{ keyword}
@item :menu-tag
Tag used in the menu when the widget is used as an option in a
@code{menu-choice} widget.

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

@vindex match@r{ keyword}
@item :match
Should be a function called with two arguments, the widget and a value,
and returning non-@code{nil} if the widget can represent the specified value.

@vindex validate@r{ keyword}
@item :validate
A function which takes a widget as an argument, and returns @code{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 @code{:error} property to a string explaining the error.

The following predefined function can be used:

@defun widget-children-validate widget
All the @code{:children} of @var{widget} must be valid.
@end defun

@vindex tab-order@r{ keyword}
@item :tab-order
Specify the order in which widgets are traversed with
@code{widget-forward} or @code{widget-backward}.  This is only partially
implemented.

@enumerate a
@item
Widgets with tabbing order @code{-1} are ignored.

@item
(Unimplemented) When on a widget with tabbing order @var{n}, go to the
next widget in the buffer with tabbing order @var{n+1} or @code{nil},
whichever comes first.

@item
When on a widget with no tabbing order specified, go to the next widget
in the buffer with a positive tabbing order, or @code{nil}
@end enumerate

@vindex parent@r{ keyword}
@item :parent
The parent of a nested widget (e.g., a @code{menu-choice} item or an
element of a @code{editable-list} widget).

@vindex sibling-args@r{ keyword}
@item :sibling-args
This keyword is only used for members of a @code{radio-button-choice} or
@code{checklist}.  The value should be a list of extra keyword
arguments, which will be used when creating the @code{radio-button} or
@code{checkbox} associated with this item.

@end table

@deffn {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 @file{.xpm} (if supported) or @file{.xbm} extension.
@end deffn

@deffn{User Option} widget-glyph-enable
If non-@code{nil}, allow glyphs to appear on displays where they are supported.
@end deffn


@menu
* link::
* url-link::
* info-link::
* push-button::
* editable-field::
* text::
* menu-choice::
* radio-button-choice::
* item::
* choice-item::
* toggle::
* checkbox::
* checklist::
* editable-list::
* group::
@end menu

@node link
@section The @code{link} Widget
@findex link@r{ widget}

Syntax:

@example
@var{type} ::= (link [@var{keyword} @var{argument}]...  [ @var{value} ])
@end example

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

By default the link will be shown in brackets.

@defopt widget-link-prefix
String to prefix links.
@end defopt

@defopt widget-link-suffix
String to suffix links.
@end defopt

@node url-link
@section The @code{url-link} Widget
@findex url-link@r{ widget}

Syntax:

@example
@var{type} ::= (url-link [@var{keyword} @var{argument}]...  @var{url})
@end example

@findex browse-url-browser-function@r{, and @code{url-link} widget}
When this link is invoked, the @acronym{WWW} browser specified by
@code{browse-url-browser-function} will be called with @var{url}.

@node info-link
@section The @code{info-link} Widget
@findex info-link@r{ widget}

Syntax:

@example
@var{type} ::= (info-link [@var{keyword} @var{argument}]...  @var{address})
@end example

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

@node  push-button
@section The @code{push-button} Widget
@findex push-button@r{ widget}

Syntax:

@example
@var{type} ::= (push-button [@var{keyword} @var{argument}]...  [ @var{value} ])
@end example

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

By default the tag will be shown in brackets.

@defopt widget-push-button-prefix
String to prefix push buttons.
@end defopt

@defopt widget-push-button-suffix
String to suffix push buttons.
@end defopt

@node editable-field
@section The @code{editable-field} Widget
@findex editable-field@r{ widget}

Syntax:

@example
@var{type} ::= (editable-field [@var{keyword} @var{argument}]... [ @var{value} ])
@end example

The @var{value}, if present, is used to initialize the @code{: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:

@table @code
@vindex size@r{ keyword}
@item :size
The width of the editable field.@*
By default the field will reach to the end of the line.

@vindex value-face@r{ keyword}
@item :value-face
Face used for highlighting the editable field.  Default is
@code{widget-field-face}, see @ref{User Interface}.

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

@vindex valid-regexp@r{ keyword}
@item :valid-regexp
By default the @code{:validate} function will match the content of the
field with the value of this attribute.  The default value is @code{""}
which matches everything.

@vindex keymap@r{ keyword}
@vindex widget-field-keymap
@item :keymap
Keymap used in the editable field.  The default value is
@code{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 @key{RET} invokes the function specified by
@code{:action}.
@end table

@node text
@section The @code{text} Widget
@findex text@r{ widget}

@vindex widget-text-keymap
This is just like @code{editable-field}, but intended for multiline text
fields.  The default @code{:keymap} is @code{widget-text-keymap}, which
does not rebind the @key{RET} key.

@node menu-choice
@section The @code{menu-choice} Widget
@findex menu-choice@r{ widget}

Syntax:

@example
@var{type} ::= (menu-choice [@var{keyword} @var{argument}]... @var{type} ... )
@end example

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

@table @code
@vindex void@r{ keyword}
@item :void
Widget type used as a fallback when the value does not match any of the
specified @var{type} arguments.

@vindex case-fold@r{ keyword}
@item :case-fold
Set this to @code{nil} if you don't want to ignore case when prompting for a
choice through the minibuffer.

@vindex children@r{ keyword}
@item :children
A list whose @sc{car} is the widget representing the currently chosen
type in the buffer.

@vindex choice@r{ keyword}
@item :choice
The current chosen type.

@vindex args@r{ keyword}
@item :args
The list of types.
@end table

@node radio-button-choice
@section The @code{radio-button-choice} Widget
@findex radio-button-choice@r{ widget}

Syntax:

@example
@var{type} ::= (radio-button-choice [@var{keyword} @var{argument}]...  @var{type} ... )
@end example

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

The following extra properties are recognized.

@table @code
@vindex entry-format@r{ keyword}
@item :entry-format
This string will be inserted for each entry in the list.
The following @samp{%} escapes are available:
@table @samp
@item %v
Replace with the buffer representation of the @var{type} widget.
@item %b
Replace with the radio button.
@item %%
Insert a literal @samp{%}.
@end table

@vindex button-args@r{ keyword}
@item :button-args
A list of keywords to pass to the radio buttons.  Useful for setting,
e.g., the @samp{:help-echo} for each button.

@vindex buttons@r{ keyword}
@item :buttons
The widgets representing the radio buttons.

@vindex children@r{ keyword}
@item :children
The widgets representing each type.

@vindex choice@r{ keyword}
@item :choice
The current chosen type

@vindex args@r{ keyword}
@item :args
The list of types.
@end table

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

@defun widget-radio-add-item widget type
Add to @code{radio-button-choice} widget @var{widget} a new radio button
item of type @var{type}.
@end defun

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

@node item
@section The @code{item} Widget
@findex item@r{ widget}

Syntax:

@example
@var{item} ::= (item [@var{keyword} @var{argument}]... @var{value})
@end example

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

@node choice-item
@section The @code{choice-item} Widget
@findex choice-item@r{ widget}

Syntax:

@example
@var{item} ::= (choice-item [@var{keyword} @var{argument}]... @var{value})
@end example

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

@node toggle
@section The @code{toggle} Widget
@findex toggle@r{ widget}

Syntax:

@example
@var{type} ::= (toggle [@var{keyword} @var{argument}]...)
@end example

The widget has two possible states, @samp{on} and @samp{off}, which
correspond to a @code{t} or @code{nil} value, respectively.

The following extra properties are recognized:

@table @code
@item :on
A string representing the @samp{on} state.  By default the string
@samp{on}.
@item :off
A string representing the @samp{off} state.  By default the string
@samp{off}.
@vindex on-glyph@r{ keyword}
@item :on-glyph
Name of a glyph to be used instead of the @samp{:on} text string, on
emacsen that supports this.
@vindex off-glyph@r{ keyword}
@item :off-glyph
Name of a glyph to be used instead of the @samp{:off} text string, on
emacsen that supports this.
@end table

@node checkbox
@section The @code{checkbox} Widget
@findex checkbox@r{ widget}

This widget has two possible states, @samp{selected} and
@samp{unselected}, which corresponds to a @code{t} or @code{nil} value.

Syntax:

@example
@var{type} ::= (checkbox [@var{keyword} @var{argument}]...)
@end example

@node checklist
@section The @code{checklist} Widget
@findex checklist@r{ widget}

Syntax:

@example
@var{type} ::= (checklist [@var{keyword} @var{argument}]...  @var{type} ... )
@end example

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

The following extra properties are recognized:

@table @code
@vindex entry-format@r{ keyword}
@item :entry-format
This string will be inserted for each entry in the list.
The following @samp{%} escapes are available:
@table @samp
@item %v
Replaced with the buffer representation of the @var{type} widget.
@item %b
Replace with the checkbox.
@item %%
Insert a literal @samp{%}.
@end table

@vindex greedy@r{ keyword}
@item :greedy
Usually a checklist will only match if the items are in the exact
sequence given in the specification.  By setting @code{:greedy} to
non-@code{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.

@vindex button-args@r{ keyword}
@item :button-args
A list of keywords to pass to the checkboxes.  Useful for setting,
e.g., the @samp{:help-echo} for each checkbox.

@vindex buttons@r{ keyword}
@item :buttons
The widgets representing the checkboxes.

@vindex children@r{ keyword}
@item :children
The widgets representing each type.

@vindex args@r{ keyword}
@item :args
The list of types.
@end table

@node editable-list
@section The @code{editable-list} Widget
@findex editable-list@r{ widget}

Syntax:

@example
@var{type} ::= (editable-list [@var{keyword} @var{argument}]... @var{type})
@end example

The value is a list, where each member represents one widget of type
@var{type}.

The following extra properties are recognized:

@table @code
@vindex entry-format@r{ keyword}
@item :entry-format
This string will be inserted for each entry in the list.
The following @samp{%} escapes are available:
@table @samp
@item %v
This will be replaced with the buffer representation of the @var{type}
widget.
@item %i
Insert the @b{[INS]} button.
@item %d
Insert the @b{[DEL]} button.
@item %%
Insert a literal @samp{%}.
@end table

@vindex insert-button-args@r{ keyword}
@item :insert-button-args
A list of keyword arguments to pass to the insert buttons.

@vindex delete-button-args@r{ keyword}
@item :delete-button-args
A list of keyword arguments to pass to the delete buttons.

@vindex append-button-args@r{ keyword}
@item :append-button-args
A list of keyword arguments to pass to the trailing insert button.

@vindex buttons@r{ keyword}
@item :buttons
The widgets representing the insert and delete buttons.

@vindex children@r{ keyword}
@item :children
The widgets representing the elements of the list.

@vindex args@r{ keyword}
@item :args
List whose @sc{car} is the type of the list elements.
@end table

@node group
@section The @code{group} Widget
@findex group@r{ widget}

This widget simply group other widgets together.

Syntax:

@example
@var{type} ::= (group [@var{keyword} @var{argument}]... @var{type}...)
@end example

The value is a list, with one member for each @var{type}.

@node Sexp Types
@chapter Sexp Types
@cindex sexp types

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

@menu
* constants::
* generic::
* atoms::
* composite::
@end menu

@node constants
@section The Constant Widgets
@cindex constant widgets

The @code{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 @code{const} widget is:

@example
@var{type} ::= (const [@var{keyword} @var{argument}]...  [ @var{value} ])
@end example

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

@deffn Widget const
This will display any valid s-expression in an immutable part of the
buffer.
@end deffn

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

@deffn Widget variable-item
An immutable symbol that is bound as a variable.
@end deffn

@deffn Widget function-item
An immutable symbol that is bound as a function.
@end deffn

@node generic
@section Generic Sexp Widget
@cindex generic sexp widget

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

The syntax for the @code{sexp} widget is:

@example
@var{type} ::= (sexp [@var{keyword} @var{argument}]...  [ @var{value} ])
@end example

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

The @code{sexp} widget takes the same keyword arguments as the
@code{editable-field} widget.  @xref{editable-field}.
@end deffn

@node atoms
@section Atomic Sexp Widgets
@cindex atomic sexp widget

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:

@example
@var{type} ::= (@var{construct} [@var{keyword} @var{argument}]...  [ @var{value} ])
@end example

The @var{value}, if present, is used to initialize the @code{: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
@code{editable-field} widget.  @xref{editable-field}.

@deffn Widget string
Allows you to edit a string in an editable field.
@end deffn

@deffn Widget regexp
Allows you to edit a regular expression in an editable field.
@end deffn

@deffn Widget character
Allows you to enter a character in an editable field.
@end deffn

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

Keywords:
@table @code
@vindex must-match@r{ keyword}
@item :must-match
If this is set to non-@code{nil}, only existing file names will be
allowed in the minibuffer.
@end table
@end deffn

@deffn Widget directory
Allows you to edit a directory name in an editable field.
Similar to the @code{file} widget.
@end deffn

@deffn Widget symbol
Allows you to edit a Lisp symbol in an editable field.
@end deffn

@deffn Widget function
Allows you to edit a lambda expression, or a function name with completion.
@end deffn

@deffn Widget variable
Allows you to edit a variable name, with completion.
@end deffn

@deffn Widget integer
Allows you to edit an integer in an editable field.
@end deffn

@deffn Widget number
Allows you to edit a number in an editable field.
@end deffn

@deffn Widget boolean
Allows you to edit a boolean.  In Lisp this means a variable which is
either @code{nil} meaning false, or non-@code{nil} meaning true.
@end deffn


@node composite
@section Composite Sexp Widgets
@cindex composite sexp widgets

The syntax for the composite widget construct is:

@example
@var{type} ::= (@var{construct} [@var{keyword} @var{argument}]...  @var{component}...)
@end example

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

@deffn Widget cons
The value of a @code{cons} widget must be a cons-cell whose @sc{car}
and @sc{cdr} have two specified types.  It uses this syntax:

@example
@var{type} ::= (cons [@var{keyword} @var{argument}]...  @var{car-type} @var{cdr-type})
@end example
@end deffn

@deffn Widget choice
The value matched by a @code{choice} widget must have one of a fixed
set of types.  The widget's syntax is as follows:

@example
@var{type} ::= (choice [@var{keyword} @var{argument}]...  @var{type} ... )
@end example

The value of a @code{choice} widget can be anything that matches any of the
@var{types}.
@end deffn

@deffn Widget list
The value of a @code{list} widget must be a list whose element types
match the specified component types:

@example
@var{type} ::= (list [@var{keyword} @var{argument}]...  @var{component-type}...)
@end example

Thus, @code{(list string number)} matches lists of two elements,
the first being a string and the second being a number.
@end deffn

@deffn Widget vector
The @code{vector} widget is like the @code{list} widget but matches
vectors instead of lists.  Thus, @code{(vector string number)} matches
vectors of two elements, the first being a string and the second being
a number.
@end deffn

The above suffice for specifying fixed size lists and vectors.  To get
variable length lists and vectors, you can use a @code{choice},
@code{set}, or @code{repeat} widget together with the @code{:inline}
keyword.  If any component of a composite widget has the
@code{: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 @code{t} or two strings (file names), you can use
the following widget specification:

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

The value of a widget of this type will either have the form
@code{(file t)} or @code{(file @var{string} @var{string})}.

This concept of @code{: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.

@deffn 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:

@example
@var{type} ::= (set [@var{keyword} @var{argument}]...  @var{permitted-element} ... )
@end example

Use @code{const} to specify each permitted element, like this:
@code{(set (const a) (const b))}.
@end deffn

@deffn Widget repeat
Specifies a list of any number of elements that fit a certain type.

@example
@var{type} ::= (repeat [@var{keyword} @var{argument}]...  @var{type})
@end example
@end deffn

@node Widget Properties
@chapter Properties
@cindex properties of widgets
@cindex widget properties

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

@defun widget-value widget
Return the current value contained in @var{widget}.
It is an error to call this function on an uninitialized widget.
@end defun

@defun widget-value-set widget value
Set the value contained in @var{widget} to @var{value}.
It is an error to call this function with an invalid @var{value}.
@end defun

@strong{Important:} You @emph{must} call @code{widget-setup} after
modifying the value of a widget before the user is allowed to edit the
widget again.  It is enough to call @code{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 @code{widget-put} and @code{widget-get}.  The property names
must begin with a @samp{:}.

@defun widget-put widget property value
In @var{widget} set @var{property} to @var{value}.
@var{property} should be a symbol, while @var{value} can be anything.
@end defun

@defun widget-get widget property
In @var{widget} return the value for @var{property}.
@var{property} should be a symbol, the value is what was last set by
@code{widget-put} for @var{property}.
@end defun

@defun widget-member widget property
Non-@code{nil} if @var{widget} has a value (even @code{nil}) for
property @var{property}.
@end defun

@defun widget-apply widget property &rest args
Apply the value of @var{property} to @var{widget}, passing @var{args}
as additional arguments to the function.  Return the result of that
function call.
@end defun

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.

@defun widget-type widget
Return the name of @var{widget}, a symbol.
@end defun

@cindex active widget
@cindex inactive widget
@cindex activate a widget
@cindex deactivate a widget
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:

@lisp
;; Examine if @var{widget} is active or not.
(if (widget-apply @var{widget} :active)
    (message "Widget is active.")
  (message "Widget is inactive.")

;; Make @var{widget} inactive.
(widget-apply @var{widget} :deactivate)

;; Make @var{widget} active.
(widget-apply @var{widget} :activate)
@end lisp

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

@lisp
(while widget
  (widget-apply widget :activate)
  (setq widget (widget-get widget :parent)))
@end lisp

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


@node Defining New Widgets
@chapter Defining New Widgets
@cindex new widgets
@cindex defining new widgets

You can define specialized widgets with @code{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.

@defun define-widget name class doc &rest args
Define a new widget type named @var{name} from @code{class}.

@var{name} and class should both be symbols, @code{class} should be one
of the existing widget types.

The third argument @var{doc} is a documentation string for the widget.

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

@itemize @bullet
@item
@lisp
(widget-create @var{name})
@end lisp

@item
@lisp
(apply widget-create @var{class} @var{args})
@end lisp
@end itemize

@end defun

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

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

The following additional keyword arguments are useful when defining new
widgets:
@table @code
@vindex convert-widget@r{ keyword}
@item :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:

@defun widget-types-convert-widget widget
Convert @code{:args} as widget types in @var{widget}.
@end defun

@defun widget-value-convert-widget widget
Initialize @code{:value} from @code{:args} in @var{widget}.
@end defun

@vindex copy@r{ keyword}
@item :copy
Function to deep copy a widget type.  It takes a shallow copy of the
widget type as an argument (made by @code{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:

@defun widget-types-copy widget
Copy @code{:args} as widget types in @var{widget}.
@end defun

@vindex value-to-internal@r{ keyword}
@item :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 @code{:value}
when the widget is created, and on any value set later with
@code{widget-value-set}.

@vindex value-to-external@r{ keyword}
@item :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 @code{:value}
when the widget is created, and on any value set later with
@code{widget-value-set}.

@vindex create@r{ keyword}
@item :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.

@vindex delete@r{ keyword}
@item :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:

@defun widget-default-delete widget
Remove @var{widget} from the buffer.
Delete all @code{:children} and @code{:buttons} in @var{widget}.
@end defun

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

@vindex value-create@r{ keyword}
@item :value-create
Function to expand the @samp{%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 @code{:children} or @code{:buttons}
to make sure they are automatically deleted.

@vindex value-delete@r{ keyword}
@item :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 @code{:children} or @code{:buttons}.

@vindex value-get@r{ keyword}
@item :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:

@defun widget-value-value-get widget
Return the @code{:value} property of @var{widget}.
@end defun

@vindex format-handler@r{ keyword}
@item :format-handler
Function to handle unknown @samp{%} escapes in the format string.  It
will be called with the widget and the character that follows the
@samp{%} as arguments.  You can set this to allow your widget to handle
non-standard escapes.

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

@vindex action@r{ keyword}
@item :action
Function to handle user initiated events.  By default, @code{:notify}
the parent.

The following predefined function can be used here:

@defun widget-parent-action widget &optional event
Tell @code{:parent} of @var{widget} to handle the @code{:action}.
Optional @var{event} is the event that triggered the action.
@end defun

@vindex prompt-value@r{ keyword}
@item :prompt-value
Function to prompt for a value in the minibuffer.  The function should
take four arguments, @var{widget}, @var{prompt}, @var{value}, and
@var{unbound} and should return a value for widget entered by the user.
@var{prompt} is the prompt to use.  @var{value} is the default value to
use, unless @var{unbound} is non-@code{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.
@end table

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

@deffn 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.
@end deffn

@node Widget Browser
@chapter Widget Browser
@cindex 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 @samp{:parent}, which avoids printing cyclic structures.

@deffn Command widget-browse @var{widget}
Create a widget browser for @var{widget}.
When called interactively, prompt for @var{widget}.
@end deffn

@deffn Command widget-browse-other-window @var{widget}
Create a widget browser for @var{widget} and show it in another window.
When called interactively, prompt for @var{widget}.
@end deffn

@deffn Command widget-browse-at @var{pos}
Create a widget browser for the widget at @var{pos}.
When called interactively, use the position of point.
@end deffn

@node  Widget Minor Mode
@chapter Widget Minor Mode
@cindex 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.

@deffn Command widget-minor-mode
Toggle minor mode for traversing widgets.
With arg, turn widget mode on if and only if arg is positive.
@end deffn

@defvar widget-minor-mode-keymap
Keymap used in @code{widget-minor-mode}.
@end defvar

@node  Utilities
@chapter Utilities
@cindex utility functions for widgets

@defun widget-prompt-value widget prompt [ value unbound ]
Prompt for a value matching @var{widget}, using @var{prompt}.
The current value is assumed to be @var{value}, unless @var{unbound} is
non-@code{nil}.
@end defun

@defun widget-get-sibling widget
Get the item which @var{widget} is assumed to toggle.
This is only meaningful for radio buttons or checkboxes in a list.
@end defun

@node  Widget Wishlist
@chapter Wishlist
@cindex todo

@itemize @bullet
@item
It should be possible to add or remove items from a list with @kbd{C-k}
and @kbd{C-o} (suggested by @sc{rms}).

@item
The @samp{[INS]} and @samp{[DEL]} buttons should be replaced by a single
dash (@samp{-}).  The dash should be a button that, when invoked, asks
whether you want to add or delete an item (@sc{rms} wanted to git rid of
the ugly buttons, the dash is my idea).

@item
The @code{menu-choice} tag should be prettier, something like the abbreviated
menus in Open Look.

@item
Finish @code{:tab-order}.

@item
Make indentation work with glyphs and proportional fonts.

@item
Add commands to show overview of object and class hierarchies to the
browser.

@item
Find a way to disable mouse highlight for inactive widgets.

@item
Find a way to make glyphs look inactive.

@item
Add @code{property-list} widget.

@item
Add @code{association-list} widget.

@item
Add @code{key-binding} widget.

@item
Add @code{widget} widget for editing widget specifications.

@item
Find clean way to implement variable length list.
See @code{TeX-printer-list} for an explanation.

@item
@kbd{C-h} in @code{widget-prompt-value} should give type specific help.

@item
Add a @code{mailto} widget.
@end itemize

@node GNU Free Documentation License
@appendix GNU Free Documentation License
@include doclicense.texi

@node Index
@unnumbered Index

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

@bye