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+/****************************************************************************
+**
+** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
+** Contact: Nokia Corporation (qt-info@nokia.com)
+**
+** This file is part of the documentation of the Qt Toolkit.
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+** In addition, as a special exception, Nokia gives you certain
+** additional rights.  These rights are described in the Nokia Qt LGPL
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+****************************************************************************/
+
+/*!
+    \page qundo.html
+    \title Overview of Qt's Undo Framework
+    \keyword Undo framework
+    \ingroup frameworks-technologies
+
+    \section1 Introduction
+
+    Qt's Undo Framework is an implementation of the Command pattern, for
+    implementing undo/redo functionality in applications.
+
+    The Command pattern is based on the idea that all editing in
+    an application is done by creating instances of command objects.
+    Command objects apply changes to the document and are stored
+    on a command stack. Furthermore, each command knows how to undo its
+    changes to bring the document back to its previous state. As long
+    as the application only uses command objects to change the state of
+    the document, it is possible to undo a sequence of commands by
+    traversing the stack downwards and calling undo
+    on each command in turn. It is also possible to redo a sequence of
+    commands by traversing the stack upwards and calling
+    redo on each command.
+
+    \section1 Classes
+
+    The framework consists of four classes:
+
+    \list
+    \i \l QUndoCommand is the base class of all commands stored on an
+            undo stack. It can apply (redo) or undo a single change in the document.
+    \i \l QUndoStack is a list of QUndoCommand objects. It contains all the
+            commands executed on the document and can roll the document's state
+            backwards or forwards by undoing or redoing them.
+    \i \l QUndoGroup is a group of undo stacks. It is useful when an application
+            contains more than one undo stack, typically one for each opened
+            document. QUndoGroup provides a single pair of undo/redo slots for all
+            the stacks in the group. It forwards undo and redo requests to
+            the active stack, which is the stack associated with the document that
+            is currently being edited by the user.
+    \i \l QUndoView is a widget which shows the contents of an undo stack. Clicking
+            on a command in the view rolls the document's state backwards or
+            forwards to that command.
+    \endlist
+
+    \section1 Concepts
+
+    The following concepts are supported by the framework:
+
+    \list
+    \i \bold{Clean state:} Used to signal when the document enters and leaves a
+        state that has been saved to disk. This is typically used to disable or
+        enable the save actions, and to update the document's title bar.
+    \i \bold{Command compression:} Used to compress sequences of commands into a
+        single command.
+        For example: In a text editor, the commands that insert individual
+        characters into the document can be compressed into a single command that
+        inserts whole sections of text. These bigger changes are more convenient
+        for the user to undo and redo.
+    \i \bold{Command macros:} A sequence of commands, all of which are undone or
+        redone in one step.
+        These simplify the task of writing an application, since a set of simpler
+        commands can be composed into more complex commands. For example, a command
+        that moves a set of selected objects in a document can be created by
+        combining a set of commands, each of which moves a single object.
+    \endlist
+
+    QUndoStack provides convenient undo and redo QAction objects that
+    can be inserted into a menu or a toolbar. The text properties of these
+    actions always reflect what command will be undone or redone when
+    they are triggered. Similarly, QUndoGroup provides undo and redo actions
+    that always behave like the undo and redo actions of the active stack.
+*/