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(widget)Introduction

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Introduction
============

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

   The basic widgets are:

`link'
     Areas of text with an associated action.  Intended for hypertext
     links embedded in text.

`push-button'
     Like link, but intended for stand-alone buttons.

`editable-field'
     An editable text field.  It can be either variable or fixed length.

`menu-choice'
     Allows the user to choose one of multiple options from a menu, each
     option is itself a widget.  Only the selected option will be
     visible in the buffer.

`radio-button-choice'
     Allows the user to choose one of multiple options by activating
     radio buttons.  The options are implemented as widgets.  All
     options will be visible in the buffer.

`item'
     A simple constant widget intended to be used in the `menu-choice'
     and `radio-button-choice' widgets.

`choice-item'
     A button item only intended for use in choices.  When invoked, the
     user will be asked to select another option from the choice widget.

`toggle'
     A simple `on'/`off' switch.

`checkbox'
     A checkbox (`[ ]'/`[X]').

`editable-list'
     Create an editable list.  The user can insert or delete items in
     the list.  Each list item is itself a widget.

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

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

  1. More complex fields than just editable text are supported.

  2. You can give the users immediate feedback if they enter invalid
     data in a text field, and sometimes prevent entering invalid data.

  3. You can have fixed sized fields, thus allowing multiple fields to
     be lined up in columns.

  4. It is simple to query or set the value of a field.

  5. Editing happens in the buffer, not in the mini-buffer.

  6. Packages using the library get a uniform look, making them easier
     for the user to learn.

  7. As support for embedded graphics improve, the widget library will
     be extended to use the GUI features.  This means that your code
     using the widget library will also use the new graphic features
     automatically.

   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 will declare the user variables, define the function
     `define-widget', and autoload the function `widget-create'.

`wid-edit.el'
     Everything else is here, there is no reason to load it explicitly,
     as it will be autoloaded when needed.