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+/****************************************************************************
+**
+** Copyright (C) 2009 Nokia Corporation and/or its subsidiary(-ies).
+** Contact: Qt Software Information (qt-info@nokia.com)
+**
+** This file is part of the documentation of the Qt Toolkit.
+**
+** $QT_BEGIN_LICENSE:LGPL$
+** No Commercial Usage
+** This file contains pre-release code and may not be distributed.
+** You may use this file in accordance with the terms and conditions
+** contained in the either Technology Preview License Agreement or the
+** Beta Release License Agreement.
+**
+** GNU Lesser General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU Lesser
+** General Public License version 2.1 as published by the Free Software
+** Foundation and appearing in the file LICENSE.LGPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU Lesser General Public License version 2.1 requirements
+** will be met: http://www.gnu.org/licenses/old-licenses/lgpl-2.1.html.
+**
+** In addition, as a special exception, Nokia gives you certain
+** additional rights. These rights are described in the Nokia Qt LGPL
+** Exception version 1.0, included in the file LGPL_EXCEPTION.txt in this
+** package.
+**
+** GNU General Public License Usage
+** Alternatively, this file may be used under the terms of the GNU
+** General Public License version 3.0 as published by the Free Software
+** Foundation and appearing in the file LICENSE.GPL included in the
+** packaging of this file.  Please review the following information to
+** ensure the GNU General Public License version 3.0 requirements will be
+** met: http://www.gnu.org/copyleft/gpl.html.
+**
+** If you are unsure which license is appropriate for your use, please
+** contact the sales department at qt-sales@nokia.com.
+** $QT_END_LICENSE$
+**
+****************************************************************************/
+
+/*!
+\page qundo.html
+\title Overview of Qt's Undo Framework
+\keyword Undo framework
+\ingroup architecture
+
+\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.
+*/