]> The Emacs Widget Library Introduction Most graphical user interface toolkits, since Motif and XView, provide a number of standard user interface controls (sometimes known as `widgets' or `gadgets'). Historically, Emacs didn't support anything like this, except for its incredible powerful text “widget”. However, since XEmacs 21.4, XEmacs has supported “native” widgets (GUI controls implemented as Lisp APIs in C for the MS Windows, Motif, Athena, and GTK toolkits) and libglade (GUI controls with an XML API for the GTK toolkit). On the other hand, Emacs does provide the necessary primitives to implement many other widgets within a text buffer, and of course this is the only way to implement self-contained controls in a text terminal. The widget package simplifies this task. Examples of some basic widgets include: link Areas of text with an associated action. Intended for hypertext linksembedded 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, eachoption is itself a widget. Only the selected option will be visible inthe buffer. radio-button-choice Allows the user to choose one of multiple options by activating radiobuttons. The options are implemented as widgets. All options will bevisible in the buffer. item A simple constant widget intended to be used in the menu-choice andradio-button-choice widgets. choice-item A button item only intended for use in choices. When invoked, the userwill 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 thelist. 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: More complex fields than just editable text are supported. You can give the user immediate feedback if he enters invalid data in atext field, and sometimes prevent entering invalid data. You can have fixed sized fields, thus allowing multiple fields to belined up in columns. It is simple to query or set the value of a field. Editing happens in a normal buffer, not in the mini-buffer. Packages using the library get a uniform look-and-feel, making them easier forthe user to learn. As support for embedded graphics has improved, the widget library willextended to support it. This means that your code using the widgetlibrary will also use the new graphic features automatically. A widget specification is implemented as a class, and new subclasses canbe derived from any class, by restricting or extending the behavior. In order to minimize the code that is loaded by users who does not create any widgets, the code has been split in two files: widget.el This declares the user variables, defines the functiondefine-widget, and autoloads the function widget-create. wid-edit.el Everything else is here. Do not load it explicitly, asit will be autoloaded when needed. User Interface A form consists of read only text for documentation and some fields, where each of the fields 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 thing the user can do within a form, namely editing the editable text fields and activating the buttons. 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. Editing text fields are created by the editable-field widget. The editing text fields are highlighted with the widget-field-face face, making them easy to find. widget-field-face — Face: widget-field-face Face used for other editing fields. 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 widget-button-press — 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 inwidget-global-map (by default the global map). mouse-2 widget-button-click — Command: widget-button-click event Invoke the button at the location of the mouse pointer. If the mousepointer is located in an editable text field, invoke the binding inwidget-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 choosebetween a number of different options. This is how you edit an optionfield. Option fields are created by the menu-choice widget. Inthe 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 embeddedbutton. Embedded buttons are not associated with a fields, but can serveany purpose, such as implementing hypertext references. They areusually created by the link widget. The ‘[ ]’ and ‘[X]’ buttons. Activating one of these will convert it to the other. This is usefulfor implementing multiple-choice fields. You can create it wit The ‘( )’ and ‘(*)’ buttons. Only one radio button in a radio-button-choice widget can beselected at any time. When you invoke one of the unselected radiobuttons, it will be selected and the previous selected radio button willbecome unselected. The ‘[Apply Form]’ ‘[Reset Form]’ buttons. These are explicit buttons made with the push-button widget. The maindifference from the link widget is that the buttons are will bedisplayed as GUI buttons when possible.enough. To make them easier to locate, buttons are emphasized in the buffer. widget-button-face — Face: widget-button-face Face used for buttons. widget-mouse-face — User Option: widget-mouse-face Face used for buttons when the mouse pointer is above it. Navigation You can use all the normal Emacs commands to move around in a form buffer, plus you will have these additional commands: TAB widget-forward — Command: widget-forward &optional count Move point count buttons or editing fields forward. M-TAB widget-backward — Command: widget-backward &optional count Move point count buttons or editing fields backward. Programming Example Here is the code to implement the user interface example (see ).(require 'widget)(eval-when-compile (require 'wid-edit))(defvar widget-example-repeat)(defun widget-example () "Create the widgets from the Widget manual." (interactive) (kill-buffer (get-buffer-create "*Widget Example*")) (switch-to-buffer (get-buffer-create "*Widget Example*")) (kill-all-local-variables) (make-local-variable 'widget-example-repeat) (widget-insert "Here is some documentation.\n\nName: ") (widget-create 'editable-field :size 13 "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-insert "Address: ") (widget-create 'editable-field "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)) 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. widget-create — Function: widget-create type [ keyword argument ] … Create and return a widget of type type.The syntax for the type argument is described in .The keyword arguments can be used to overwrite the keyword argumentsthat are part of type. widget-delete — Function: widget-delete widget Delete widget and remove it from the buffer. widget-setup — Function: widget-setup Setup a buffer to support widgets.This should be called after creating all the widgets and before allowingthe 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. 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. widget-keymap — Const: widget-keymap A keymap with the global keymap as its parent.TAB and C-TAB are bound to widget-forward andwidget-backward, respectively. RET and mouse-2are bound to widget-button-press andwidget-button-. widget-global-map — Variable: widget-global-map Keymap used by widget-button-press and widget-button-clickwhen not on a button. By default this is global-map. Basic Types The syntax of a type specification is given below: 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. There following keyword arguments that 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, andsurrounded by brackets. widget-button-prefix — User Option: widget-button-prefix String to prefix buttons. widget-button-suffix — User Option: widget-button-suffix String to suffix buttons. ‘%{’‘%}’ The text inside will be displayed in the face specified by:sample-face. ‘%v’ This will be replaced with the buffer representation of the widget'svalue. What this is depends on the widget type. ‘%d’ Insert the string specified by :doc here. ‘%h’ Like ‘%d’, with the following modifications: If the documentationstring is more than one line, it will add a button which will togglebetween showing only the first line, and showing the full text.Furthermore, if there is no :doc property in the widget, it willinstead examine the :documentation-property property. If it is alambda expression, it will be called with the widget's value as anargument, and the result will be used as the documentation text. ‘%t’ Insert the string specified by :tag here, or the princrepresentation 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’ or ‘%h’ escape in the formatstring. :tag The string inserted by the ‘%t’ escape in the formatstring. :tag-glyph Name of image to use instead of the string specified by `:tag' onEmacsen that supports it. :help-echo Message displayed whenever you move to the widget with eitherwidget-forward or widget-backward. :indent An integer indicating the absolute number of spaces to indent childrenof this widget. :offset An integer indicating how many extra spaces to add to the widget'sgrandchildren compared to this widget. :extra-offset An integer indicating how many extra spaces to add to the widget'schildren 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 argumentis the widget itself, the second argument is the widget that waschanged, and the third argument is the event leading to the change, ifany. In editable fields, this includes all insertions, deletions,etc. To watch only for “final” actions, redefine the:action callback. :menu-tag Tag used in the menu when the widget is used as an option in amenu-choice widget. :menu-tag-get Function used for finding the tag when the widget is used as an optionin a menu-choice widget. By default, the tag used will be either the:menu-tag or :tag property if present, or the princrepresentation 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 thewidget's current value is valid for the widget. Otherwise it shouldreturn 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: widget-children-validate — Function: widget-children-validate widget All the :children of widget must be valid. :tab-order Specify the order in which widgets are traversed withwidget-forward or widget-backward. This is only partiallyimplemented. Widgets with tabbing order -1 are ignored. (Unimplemented) When on a widget with tabbing order n, go to thenext widget in the buffer with tabbing order n+1 or nil,whichever comes first. When on a widget with no tabbing order specified, go to the next widgetin the buffer with a positive tabbing order, or nil :parent The parent of a nested widget (e.g. a menu-choice item or anelement of an editable-list widget). :sibling-args This keyword is only used for members of a radio-button-choice orchecklist. The value should be a list of extra keywordarguments, which will be used when creating the radio-button orcheckbox associated with this item. widget-glyph-directory — User Option: widget-glyph-directory Directory where glyphs are found.Widget will look here for a file with the same name as specified for theimage, with either a ‘.xpm’ (if supported) or ‘.xbm’ extension. widget-glyph-enable — User Option: widget-glyph-enable If non-nil, allow glyphs to appear on displays where they are supported. 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. widget-link-prefix — User Option: widget-link-prefix String to prefix links. widget-link-suffix — User Option: widget-link-suffix String to suffix links. 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. The info-link Widget Syntax: TYPE ::= (info-link [KEYWORD ARGUMENT]... ADDRESS) When this link is invoked, the built-in info browser is started on address. 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. widget-push-button-prefix — User Option: widget-push-button-prefix String to prefix push buttons. widget-push-button-suffix — User Option: widget-push-button-suffix String to suffix push buttons. 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 field. This widget will match all string values. The following extra properties are recognized. :size The minimum width of the editable field.By default the field will reach to the end of the line. If thecontent is too large, the displayed representation will expand tocontain it. The content is not truncated to size. :value-face Face used for highlighting the editable field. Default iswidget-field-face. :secret Character used to display the value. You can set this to e.g. ?*if the field contains a password or other secret information. Bydefault, the value is not secret. :valid-regexp By default the :validate function will match the content of thefield with the value of this attribute. The default value is ""which matches everything. :keymap Keymap used in the editable field. The default value iswidget-field-keymap, which allows you to use all the normalediting commands, even if the buffer's major mode suppress some of them.Pressing return invokes the function specified by :action. 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 return key. 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 thespecified type arguments. :case-fold Set this to nil if you don't want to ignore case when prompting for achoice through the minibuffer. :children A list whose car is the widget representing the currently chosen type inthe buffer. :choice The current chosen type :args The list of types. The radio-button-choice Widget Syntax: TYPE ::= (radio-button-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. 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 radio button. ‘%%’ Insert a literal ‘%’. button-args A list of keywords to pass to the radio buttons. Useful for settinge.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. widget-radio-add-item — Function: widget-radio-add-item widget type Add to radio-button-choice widget widget a new radio button item of typetype. 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. 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. 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. 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 String representing the `on' state. By default the string ‘on’. :off 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 emacsenthat supports it. :off-glyph Name of a glyph to be used instead of the `:off' text string, on emacsenthat supports it. The checkbox Widget The widget has two possible states, `selected' and `unselected', which corresponds to a t or nil value. Syntax: TYPE ::= (checkbox [KEYWORD ARGUMENT]...) The checklist Widget Syntax: TYPE ::= (checklist [KEYWORD ARGUMENT]... TYPE ... ) The type arguments represents each checklist item. The widget's value will be a list containing the values of all ticked 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 exactsequence given in the specification. By setting :greedy tonon-nil, it will allow the items to appear in any sequence. However, ifyou extract the values they will be in the sequence given in thechecklist. I.e. the original sequence is forgotten. button-args A list of keywords to pass to the checkboxes. Useful for settinge.g. the ‘:help-echo’ for each checkbox. :buttons The widgets representing the checkboxes. :children The widgets representing each type. :args The list of types. 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 typewidget. ‘%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. The group Widget This widget simply groups other widgets together. Syntax: TYPE ::= (group [KEYWORD ARGUMENT]... TYPE...) The value is a list, with one member for each type. Sexp Types A number of widgets for editing s-expressions (lisp types) are also available. These basically fall in the following categories. 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. const — Widget: const This will display any valid s-expression in an immutable part of thebuffer. 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. variable-item — Widget: variable-item An immutable symbol that is bound as a variable. function-item — Widget: function-item An immutable symbol that is bound as a function. 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 ]) sexp — Widget: sexp This will allow you to edit any valid s-expression in an editable bufferfield.The sexp widget takes the same keyword arguments as theeditable-field widget. Atomic Sexp Widgets. The atoms are s-expressions that does not consist of other s-expressions. A string is an atom, 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 ::= (NAME [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. I.e. the string widget can only be initialized with a string. All the atom widgets take the same keyword arguments as the editable-field widget. string — Widget: string Allows you to edit a string in an editable field. regexp — Widget: regexp Allows you to edit a regular expression in an editable field. character — Widget: character Allows you to enter a character in an editable field. file — Widget: file Allows you to edit a file name in an editable field. If you invokethe tag button, you can edit the file name in the mini-buffer withcompletion.Keywords: :must-match If this is set to non-nil, only existing file names will be allowed inthe minibuffer. directory — Widget: directory Allows you to edit a directory name in an editable field.Similar to the file widget. symbol — Widget: symbol Allows you to edit a lisp symbol in an editable field. function — Widget: function Allows you to edit a lambda expression, or a function name with completion. variable — Widget: variable Allows you to edit a variable name, with completion. integer — Widget: integer Allows you to edit an integer in an editable field. number — Widget: number Allows you to edit a number in an editable field. boolean — Widget: boolean Allows you to edit a boolean. In lisp this means a variable which iseither nil meaning false, or non-nil meaning true. Composite Sexp Widgets. The syntax for the composite are TYPE ::= (NAME [KEYWORD ARGUMENT]... COMPONENT...) Where each component must be a widget type. Each component widget will be displayed in the buffer, and be editable to the user. cons — Widget: cons The value of a cons widget is a cons-cell where the car is thevalue of the first component and the cdr is the value of the secondcomponent. There must be exactly two components. list — Widget: list The value of a list widget is a list containing the value ofeach of its component. vector — Widget: vector The value of a vector widget is a vector containing the value ofeach of its component. 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 widgets together with the :inline keywords. 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 arguments should either by the symbol t or two files, 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 is probably 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. choice — Widget: choice Allows you to edit a sexp which may have one of a fixed set of types.It is currently implemented with the choice-menu basic widget,and has a similar syntax. set — Widget: set Allows you to specify a type which must be a list whose elements allbelong to given set. The elements of the list is not significant. Thisis implemented on top of the checklist basic widget, and has asimilar syntax. repeat — Widget: repeat Allows you to specify a variable length list whose members are all ofthe same type. Implemented on top of the `editable-list' basic widget,and has a similar syntax. Properties You can examine or set the value of a widget by using the widget object that was returned by widget-create. widget-value — Function: widget-value widget Return the current value contained in widget.It is an error to call this function on an uninitialized widget. widget-value-set — 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 ‘:’. widget-put — Function: widget-put widget property value In widget set property to value.property should be a symbol, while value can be anything. widget-get — Function: widget-get widget property In widget return the value for property.property should be a symbol, the value is what was last set bywidget-put for property. widget-member — 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. widget-type — 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 itself 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 itself 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. Defining New Widgets You can define specialized widgets with define-widget. It allows you to create a shorthand for more complex widgets. This includes specifying component widgets and new default values for the keyword arguments. define-widget — 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 oneof 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 willcreate 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 just want to specify defaults for keywords with no complex conversions, you can use identity as your :convert-widget function. The following additional keyword arguments are useful when defining new widgets: :convert-widget Method to convert type-specific components of a widget type beforeinstantiating a widget of that type. Not normally called from usercode, it is invoked by widget-convert. Typical operationsinclude converting types of child widgets to widget instances andconverting values from external format (i.e., as expected by thecalling code) to internal format (which is often different for theconvenience of widget manipulation). It takes a widget type as anargument, and returns the converted widget type. When a widget iscreated, the value of this property is called for the widget type, thenfor all the widget's parent types, most derived first. (The property isreevaluated for each parent type.)The following predefined functions can be used here: widget-types-convert-widget — Function: widget-types-convert-widget widget Convert each member of :args in widget from a widget typeto a widget. widget-value-convert-widget — Function: widget-value-convert-widget widget Initialize :value from (car :args) in widget, andreset :args. :copy A method to implement deep copying of the type. Any member of thewidget which might be changed in place (rather than replaced) should becopied by this method. (widget-copy uses copy-sequence toensure that the top-level list is a copy.) This particularly applies tochild widgets. :value-to-internal Function to convert the value to the internal format. The functiontakes two arguments, a widget and an external value. It returns theinternal value. The function is called on the present :valuewhen the widget is created, and on any value set later withwidget-value-set. :value-to-external Function to convert the value to the external format. The functiontakes two arguments, a widget and an internal value, and returns theinternal value. The function is called on the present :valuewhen the widget is created, and on any value set later withwidget-value-set. :create Function to create a widget from scratch. The function takes oneargument, a widget, and inserts it in the buffer. Not normally calledfrom user code. Instead, call widget-create or relatedfunctions, which take a type argument, (usually) convert it to a widget,call the :create function to insert it in the buffer, and thenreturn the (possibly converted) widget.The default, widget-default-create, is invariably appropriate.(None of the standard widgets specify :create.) :delete Function to delete a widget. The function takes one argument, a widget,and should remove all traces of the widget from the buffer. :value-create Function to expand the ‘%v’ escape in the format string. It willbe called with the widget as its argument and should insert arepresentation of the widget's value in the buffer. :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 toremove the text, but it should release markers and delete nested widgetsif such have been used.The following predefined function can be used here: widget-children-value-delete — Function: widget-children-value-delete widget Delete all :children and :buttons in widget. :value-get Function to extract the value of a widget, as it is displayed in thebuffer.The following predefined function can be used here: widget-value-value-get — Function: widget-value-value-get widget Return the :value property of widget. :format-handler Function to handle unknown ‘%’ escapes in the format string. Itwill be called with the widget and the escape character 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 handleunknown escape sequences. It will handle the ‘%h’ and any futureescape sequences as well as give an error for unknown escapes. :action Function to handle user initiated events. By default, :notifythe parent. Actions normally do not include mere edits, but refer tothings like invoking buttons or hitting enter in an editable field. Towatch for any change, redefine the :notify callback.The following predefined function can be used here: widget-parent-action — 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 shouldtake four arguments, widget, prompt, value, andunbound and should return a value for widget entered by the user.prompt is the prompt to use. value is the default value touse, unless unbound is non-nil. In this case there is no defaultvalue. The function should read the value using the method most naturalfor this widget and does not have to check whether it matches. If you want to define a new widget from scratch, use the default widget as its base. default — Widget: default Widget used as a base for other widgets.It provides most of the functionality that is referred to as “bydefault” in this text. In implementing complex hierarchical widgets (e.g., using the ‘group’ widget), the following functions may be useful. The syntax for the type arguments to these functions is described in . widget-create-child-and-convert — Function: widget-create-child-and-convert parent type &rest args As a child of parent, create a widget with type type andvalue value. type is copied, and the :widget-contvertmethod is applied to the optional keyword arguments from args. widget-create-child — Function: widget-create-child parent type As a child of parent, create a widget with type type.type is copied, but no conversion method is applied. widget-create-child-value — Function: widget-create-child-value parent type value As a child of parent, create a widget with type type andvalue value. type is copied, but no conversion method isapplied. widget-convert — Function: widget-convert type &rest args Convert type to a widget without inserting it in the buffer.The optional args are additional keyword arguments.The widget's :args property is set from the longest tail ofargs whose ‘cdr’ is not a keyword, or if that is null, fromthe longest tail of type's :args property whose cdr is nota keyword. Keyword arguments from args are set, and the:value property (if any) is converted from external to internalformat. widget-convert is typically not called from user code; rather it is called implicitly through the ‘widget-create*’ functions. 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. widget-browse — Command: widget-browse WIDGET Create a widget browser for WIDGET.When called interactively, prompt for WIDGET. widget-browse-other-window — Command: widget-browse-other-window WIDGET Create a widget browser for WIDGET and show it in another window.When called interactively, prompt for WIDGET. widget-browse-at — Command: widget-browse-at POS Create a widget browser for the widget at POS.When called interactively, use the position of point. Widget Minor Mode There is a minor mode for manipulating widgets in major modes that doesn't provide any support for widgets themselves. This is mostly intended to be useful for programmers doing experiments. widget-minor-mode — Command: widget-minor-mode Toggle minor mode for traversing widgets.With arg, turn widget mode on if and only if arg is positive. widget-minor-mode-keymap — Variable: widget-minor-mode-keymap Keymap used in widget-minor-mode. Utilities. widget-prompt-value — 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 isnon-nil. widget-get-sibling — Function: widget-get-sibling widget Get the item widget is assumed to toggle.This is only meaningful for radio buttons or checkboxes in a list. Wishlist It should be possible to add or remove items from a list with C-kand C-o (suggested by rms). The ‘[INS]’ and ‘[DEL]’ buttons should be replaced by a singledash (‘-’). The dash should be a button that, when invoked, askwhether you want to add or delete an item (rms wanted to git rid ofthe ugly buttons, the dash is my idea). The menu-choice tag should be prettier, something like the abbreviatedmenus in Open Look. Finish :tab-order. Make indentation work with glyphs and proportional fonts. Add commands to show overview of object and class hierarchies to thebrowser. Find a way to disable mouse highlight for inactive widgets. Find a way to make glyphs look inactive. Add property-list widget. Add association-list widget. Add key-binding widget. Add widget widget for editing widget specifications. Find clean way to implement variable length list.See TeX-printer-list for an explanation. C-h in widget-prompt-value should give type specific help. A mailto widget. C-e e in a fixed size field should go to the end of the text inthe field, not the end of the field itself. Use an overlay instead of markers to delimit the widget. Createaccessors for the end points. Clicking on documentation links should call describe-function orwidget-browse-other-window and friends directly, instead of goingthrough apropos. If more than one function is valid for thesymbol, it should pop up a menu. Internals This (very brief!) section provides a few notes on the internal structure and implementation of Emacs widgets. Avoid relying on this information. (We intend to improve it, but this will take some time.) To the extent that it actually describes APIs, the information will be moved to appropriate sections of the manual in due course. The Widget and Type Structures Widgets and types are currently both implemented as lists. A symbol may be defined as a type name using define-widget. See . A type is a list whose car is a previously defined type name, nil, or (recursively) a type. The car is the class or parent type of the type, and properties which are not specified in the new type will be inherited from ancestors. Probably the only type without a class should be the default type. The cdr of a type is a plist whose keys are widget property keywords. A type or type name may also be referred to as an unconverted widget. A converted widget or widget instance is a list whose car is a type name or a type, and whose cdr is a property list. Furthermore, all children of the converted widget must be converted. Finally, in the process of appropriate parts of the list structure are copied to ensure that changes in values of one instance do not affect another's.