source: trunk/doc/src/richtext.qdoc@ 9

/****************************************************************************
**
** 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.
**
** $QT_BEGIN_LICENSE:LGPL$
** Commercial Usage
** Licensees holding valid Qt Commercial licenses may use this file in
** accordance with the Qt Commercial License Agreement provided with the
** Software or, alternatively, in accordance with the terms contained in
** a written agreement between you and Nokia.
**
** 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 richtext.html
\nextpage Rich Text Document Structure

\title Rich Text Processing
\ingroup architecture
\ingroup text-processing
\brief An overview of Qt's rich text processing, editing and display features.

The Scribe framework provides a set of classes for reading and manipulating
structured rich text documents. Unlike previous rich text support in Qt, the
new classes are centered around the QTextDocument class rather than raw
textual information. This enables the developer to create and modify
structured rich text documents without having to prepare content in an
intermediate markup format.

The information within a document can be accessed via two complementary
interfaces: A cursor-based interface is used for editing, and a read-only
hierarchical interface provides a high level overview of the document
structure. The main advantage of the cursor-based interface is that the
text can be edited using operations that mimic a user's interaction with
an editor, without losing the underlying structure of the document. The
read-only hierarchical interface is most useful when performing operations
such as searching and document export.

This document is divided up into chapters for convenient reference:

\list
\i \l{Rich Text Document Structure} outlines
   the different kinds of elements in a QTextDocument, and describes how
   they are arranged in a document structure.
\i \l{The QTextCursor Interface} explains how rich
   text documents can be edited using the cursor-based interface.
\i \l{Common Rich Text Editing Tasks} examines some
   common tasks that involve reading or manipulating rich text documents.
\i \l{Advanced Rich Text Processing} examines advanced rich text editing tasks.
\i \l{Supported HTML Subset} lists the HTML tags supported by QTextDocument.
\endlist

See also the list of \l{Text Processing Classes}.

*/

/*!
\page richtext-structure.html
\contentspage richtext.html Contents
\previouspage Rich Text Processing
\nextpage The QTextCursor Interface

\title Rich Text Document Structure

\tableofcontents

The structured representation of a text document presents its contents as
a hierarchy of text blocks, frames, tables, and other objects. These provide
a logical structure to the document and describe how their contents will be
displayed. Generally, frames and tables are used to group other
structures while text blocks contain the actual textual information.

New elements are created and inserted into the document programmatically
\l{richtext-cursor.html}{with a QTextCursor} or by using an editor
widget, such as QTextEdit. Elements can be given a particular format when
they are created; otherwise they take the cursor's current format for the
element.

\table
\row
\i \inlineimage richtext-document.png
\i \bold{Basic structure}

The "top level" of a document might be populated in the way shown.
Each document always contains a root frame, and this always contains
at least one text block.

For documents with some textual content, the root
frame usually contains a sequence of blocks and other elements.

Sequences of frames and tables are always separated by text blocks in a
document, even if the text blocks contain no information. This ensures that
new elements can always be inserted between existing structures.
\endtable

In this chapter, we look at each of the structural elements
used in a rich text document, outline their features and uses, and show
how to examine their contents. Document editing is described in
\l{richtext-cursor.html}{The QTextCursor Interface}.

\section1 Rich Text Documents

QTextDocument objects contain all the information required to construct
rich text documents for use with a QTextEdit widget or in a custom editor.
Although QTextEdit makes it easy to display and edit rich text, documents
can also be used independently of any editor widget, for example:

\snippet doc/src/snippets/code/doc_src_richtext.qdoc 0

Alternatively, they can be extracted from an existing editor:

\snippet doc/src/snippets/code/doc_src_richtext.qdoc 1

This flexibility enables applications to handle multiple rich text
documents without the overhead of multiple editor widgets, or requiring
documents to be stored in some intermediate format.

An empty document contains a root frame which itself contains a single
empty text block. The \l{richtext-cursor.html}{text cursor interface}
automatically inserts new document elements into the root frame, and
ensures that it is padded with empty blocks where necessary.

We obtain the root frame in the following manner:

\snippet doc/src/snippets/textdocument-frames/xmlwriter.h 0
\snippet doc/src/snippets/textdocument-frames/xmlwriter.cpp 0

When navigating the document structure, it is useful to begin at the
root frame because it provides access to the entire document structure.

\section1 Document Elements

Rich text documents usually consist of common elements such as paragraphs,
frames, tables, and lists. These are represented in a QTextDocument
by the QTextBlock, QTextFrame, QTextTable, and QTextList classes.
Unlike the other elements in a document, images are represented by
specially formatted text fragments. This enables them to be placed
formatted inline with the surrounding text.

The basic structural building blocks in documents are QTextBlock and
QTextFrame. Blocks themselves contain fragments of rich text
(QTextFragment), but these do not directly influence the high level
structure of a document.

Elements which can group together other document elements are typically
subclasses of QTextObject, and fall into two categories: Elements that
group together text blocks are subclasses of QTextBlockGroup, and those
that group together frames and other elements are subclasses of QTextFrame.

\section2 Text Blocks

Text blocks are provided by the QTextBlock class.

Text blocks group together fragments of text with different character formats,
and are used to represent paragraphs in the document. Each block
typically contains a number of text fragments with different styles.
Fragments are created when text is inserted into the document, and more
of them are added when the document is edited. The document splits, merges,
and removes fragments to efficiently represent the different styles
of text in the block.

The fragments within a given block can be examined by using a
QTextBlock::iterator to traverse the block's internal structure:

\snippet doc/src/snippets/textblock-fragments/xmlwriter.cpp 3
\snippet doc/src/snippets/textblock-fragments/xmlwriter.cpp 5
\snippet doc/src/snippets/textblock-fragments/xmlwriter.cpp 6

Blocks are also used to represent list items. As a result, blocks can
define their own character formats which contain information about
block-level decoration, such as the type of bullet points used for
list items. The formatting for the block itself is described by the
QTextBlockFormat class, and describes properties such as text alignment,
indentation, and background color.

Although a given document may contain complex structures, once we have a
reference to a valid block in the document, we can navigate between each
of the text blocks in the order in which they were written:

\snippet doc/src/snippets/textblock-fragments/xmlwriter.cpp 0
\snippet doc/src/snippets/textblock-fragments/xmlwriter.cpp 1
\snippet doc/src/snippets/textblock-fragments/xmlwriter.cpp 2

This method is useful for when you want to extract just the rich text from a
document because it ignores frames, tables, and other types of structure.

QTextBlock provides comparison operators that make it easier to manipulate
blocks: \l{QTextBlock::operator==()}{operator==()} and
\l{QTextBlock::operator!=()}{operator!=()} are used to test whether two
blocks are the same, and \l{QTextBlock::operator<()}{operator<()} is used
to determine which one occurs first in a document.

\section2 Frames

Frames are provided by the QTextFrame class.

Text frames group together blocks of text and child frames, creating
document structures that are larger than paragraphs. The format of a frame
specifies how it is rendered and positioned on the page. Frames are
either inserted into the text flow, or they float on the left or right
hand side of the page.
Each document contains a root frame that contains all the other document
elements. As a result, all frames except the root frame have a parent
frame.

Since text blocks are used to separate other document elements, each
frame will always contain at least one text block, and zero or more
child frames. We can inspect the contents of a frame by using a
QTextFrame::iterator to traverse the frame's child elements:

\snippet doc/src/snippets/textdocument-frames/xmlwriter.cpp 1
\snippet doc/src/snippets/textdocument-frames/xmlwriter.cpp 2

Note that the iterator selects both frames and blocks, so it is necessary
to check which it is referring to. This allows us to navigate the document
structure on a frame-by-frame basis yet still access text blocks if
required. Both the QTextBlock::iterator and QTextFrame::iterator classes
can be used in complementary ways to extract the required structure from
a document.

\section2 Tables

Tables are provided by the QTextTable class.

Tables are collections of cells that are arranged in rows and columns.
Each table cell is a document element with its own character format, but it
can also contain other elements, such as frames and text blocks. Table cells
are automatically created when the table is constructed, or when extra rows
or columns are added. They can also be moved between tables.

QTextTable is a subclass of QTextFrame, so tables are treated like frames
in the document structure. For each frame that we encounter in the
document, we can test whether it represents a table, and deal with it in a
different way:

\snippet doc/src/snippets/textdocument-tables/xmlwriter.cpp 0
\snippet doc/src/snippets/textdocument-tables/xmlwriter.cpp 1

The cells within an existing table can be examined by iterating through
the rows and columns.

\snippet doc/src/snippets/textdocument-tables/mainwindow.cpp 9
\snippet doc/src/snippets/textdocument-tables/mainwindow.cpp 10
\snippet doc/src/snippets/textdocument-tables/mainwindow.cpp 11
\snippet doc/src/snippets/textdocument-tables/mainwindow.cpp 12


\section2 Lists

Lists are provided by the QTextList class.

Lists are sequences of text blocks that are formatted in the usual way, but
which also provide the standard list decorations such as bullet points and
enumerated items. Lists can be nested, and will be indented if the list's
format specifies a non-zero indentation.

We can refer to each list item by its index in the list:

\snippet doc/src/snippets/textdocument-listitems/mainwindow.cpp 0
\snippet doc/src/snippets/textdocument-listitems/mainwindow.cpp 1
\snippet doc/src/snippets/textdocument-listitems/mainwindow.cpp 2

Since QTextList is a subclass of QTextBlockGroup, it does not group the
list items as child elements, but instead provides various functions for
managing them. This means that any text block we find when traversing a
document may actually be a list item. We can ensure that list items are
correctly identified by using the following code:

\snippet doc/src/snippets/textdocument-listitems/mainwindow.cpp 3
\snippet doc/src/snippets/textdocument-listitems/mainwindow.cpp 4
\snippet doc/src/snippets/textdocument-listitems/mainwindow.cpp 5
\snippet doc/src/snippets/textdocument-listitems/mainwindow.cpp 6
\snippet doc/src/snippets/textdocument-listitems/mainwindow.cpp 7


\section2 Images

Images in QTextDocument are represented by text fragments that reference
external images via the resource mechanism. Images are created using the
cursor interface, and can be modified later by changing the character
format of the image's text fragment:

\snippet doc/src/snippets/textdocument-imageformat/main.cpp 0
\snippet doc/src/snippets/textdocument-imageformat/main.cpp 1
\snippet doc/src/snippets/textdocument-imageformat/main.cpp 2

The fragment that represents the image can be found by iterating over
the fragments in the text block that contains the image.
*/

/*!
\page richtext-cursor.html
\contentspage richtext.html Contents
\previouspage Rich Text Document Structure
\nextpage Common Rich Text Editing Tasks

\title The QTextCursor Interface

\tableofcontents

The QTextCursor interface allows documents and their structure to be
edited in a way that should be familiar to most users of text editors and
document editing software. Rich text documents can have multiple cursors
associated with them, and each of these contains information about their
position in the document and any selections that they may hold. This
cursor-based paradigm makes common operations, such as cutting and pasting
text, simple to implement programmatically, yet it also allows more complex
editing operations to be performed on the document.

This chapter describes most of the common editing operations that you
will need to perform using a cursor, from basic insertion of text and
document elements to more complex manipulation of document structures.

\section1 Cursor-Based Editing

At the simplest level, text documents are made up of a string of characters,
marked up in some way to represent the block structure of the text within the
document. QTextCursor provides a cursor-based interface that allows the
contents of a QTextDocument to be manipulated at the character level. Since
the elements (blocks, frames, tables, etc.) are also encoded in the character
stream, the document structure can itself be changed by the cursor.

The cursor keeps track of its location within its parent document, and can
report information about the surrounding structure, such as the enclosing
text block, frame, table, or list. The formats of the enclosing structures
can also be directly obtained through the cursor.

\section2 Using a Cursor

The main use of a cursor is to insert or modify text within a block.
We can use a text editor's cursor to do this:

\snippet doc/src/snippets/textblock-formats/main.cpp 0

Alternatively, we can obtain a cursor directly from a document:

\snippet doc/src/snippets/textdocument-images/main.cpp 0

The cursor is positioned at the start of the document so that we can write
into the first (empty) block in the document.

\section2 Grouping Cursor Operations

A series of editing operations can be packaged together so that they can
be replayed, or undone together in a single action. This is achieved by
using the \c beginEditBlock() and \c endEditBlock() functions in the
following way, as in the following example where we select the word that
contains the cursor:

\snippet doc/src/snippets/textdocument-selections/mainwindow.cpp 0

If editing operations are not grouped, the document automatically records
the individual operations so that they can be undone later. Grouping
operations into larger packages can make editing more efficient both for
the user and for the application, but care has to be taken not to group too
many operations together as the user may want find-grained control over the
undo process.

\section2 Multiple Cursors

Multiple cursors can be used to simultaneously edit the same document,
although only one will be visible to the user in a QTextEdit widget.
The QTextDocument ensures that each cursor writes text correctly and
does not interfere with any of the others.

\omit
\snippet doc/src/snippets/textdocument-cursors/main.cpp 0
\snippet doc/src/snippets/textdocument-cursors/main.cpp 1
\endomit

\section1 Inserting Document Elements

QTextCursor provides several functions that can be used to change the
structure of a rich text document. Generally, these functions allow
document elements to be created with relevant formatting information,
and they are inserted into the document at the cursor's position.

The first group of functions insert block-level elements, and update the
cursor position, but they do not return the element that was inserted:

\list
\i \l{QTextCursor::insertBlock()}{insertBlock()} inserts a new text block
   (paragraph) into a document at the cursor's position, and moves the
   cursor to the start of the new block.
\i \l{QTextCursor::insertFragment()}{insertFragment()} inserts an existing
   text fragment into a document at the cursor's position.
\i \l{QTextCursor::insertImage()}{insertImage()} inserts an image into a
   document at the cursor's position.
\i \l{QTextCursor::insertText()}{insertText()} inserts text into the
   document at the cursor's position.
\endlist

You can examine the contents of the element that was inserted through the
cursor interface.

The second group of functions insert elements that provide structure to
the document, and return the structure that was inserted:

\list
\i \l{QTextCursor::insertFrame()}{insertFrame()} inserts a frame into the
   document \e after the cursor's current block, and moves the cursor to
   the start of the empty block in the new frame.
\i \l{QTextCursor::insertList()}{insertList()} inserts a list into the
   document at the cursor's position, and moves the cursor to the start
   of the first item in the list.
\i \l{QTextCursor::insertTable()}{insertTable()} inserts a table into
   the document \e after the cursor's current block, and moves the cursor
   to the start of the block following the table.
\endlist

These elements either contain or group together other elements in the
document.

\section2 Text and Text Fragments

Text can be inserted into the current block in the current character
format, or in a custom format that is specified with the text:

\snippet doc/src/snippets/textdocument-charformats/main.cpp 0

Once the character format has been used with a cursor, that format becomes
the default format for any text inserted with that cursor until another
character format is specified.

If a cursor is used to insert text without specifying a character format,
the text will be given the character format used at that position in the
document.

\section2 Blocks

Text blocks are inserted into the document with the
\l{QTextCursor::insertBlock()}{insertBlock()} function.

\snippet doc/src/snippets/textblock-formats/main.cpp 1

The cursor is positioned at the start of the new block.

\section2 Frames

Frames are inserted into a document using the cursor, and will be placed
within the cursor's current frame \e after the current block.
The following code shows how a frame can be inserted between two text
blocks in a document's root frame. We begin by finding the cursor's
current frame:

\snippet doc/src/snippets/textdocument-frames/mainwindow.cpp 0

We insert some text in this frame then set up a frame format for the
child frame:

\snippet doc/src/snippets/textdocument-frames/mainwindow.cpp 1

The frame format will give the frame an external margin of 32 pixels,
internal padding of 8 pixels, and a border that is 4 pixels wide.
See the QTextFrameFormat documentation for more information about
frame formats.

The frame is inserted into the document after the preceding text:

\snippet doc/src/snippets/textdocument-frames/mainwindow.cpp 2

We add some text to the document immediately after we insert the frame.
Since the text cursor is positioned \e{inside the frame} when it is inserted
into the document, this text will also be inserted inside the frame.

Finally, we position the cursor outside the frame by taking the last
available cursor position inside the frame we recorded earlier:

\snippet doc/src/snippets/textdocument-frames/mainwindow.cpp 3

The text that we add last is inserted after the child frame in the
document. Since each frame is padded with text blocks, this ensures that
more elements can always be inserted with a cursor.

\section2 Tables

Tables are inserted into the document using the cursor, and will be
placed within the cursor's current frame \e after the current block:

\snippet doc/src/snippets/textdocument-tables/mainwindow.cpp 0
\snippet doc/src/snippets/textdocument-tables/mainwindow.cpp 3

Tables can be created with a specific format that defines the overall
properties of the table, such as its alignment, background color, and
the cell spacing used. It can also determine the constraints on each
column, allowing each of them to have a fixed width, or resize according
to the available space.

\snippet doc/src/snippets/textdocument-tables/mainwindow.cpp 2

The columns in the table created above will each take up a certain
percentage of the available width. Note that the table format is
optional; if you insert a table without a format, some sensible
default values will be used for the table's properties.

Since cells can contain other document elements, they too can be
formatted and styled as necessary.

Text can be added to the table by navigating to each cell with the cursor
and inserting text.

\snippet doc/src/snippets/textdocument-tables/mainwindow.cpp 4

We can create a simple timetable by following this approach:

\snippet doc/src/snippets/textdocument-tables/mainwindow.cpp 5
\snippet doc/src/snippets/textdocument-tables/mainwindow.cpp 6
\snippet doc/src/snippets/textdocument-tables/mainwindow.cpp 7
\snippet doc/src/snippets/textdocument-tables/mainwindow.cpp 8

\section2 Lists

Lists of block elements can be automatically created and inserted into the
document at the current cursor position. Each list that is created in this
way requires a list format to be specified:

\snippet doc/src/snippets/textdocument-lists/mainwindow.cpp 0

The above code first checks whether the cursor is within an existing list
and, if so, gives the list format for the new list a suitable level of
indentation. This allows nested lists to be created with increasing
levels of indentation. A more sophisticated implementation would also use
different kinds of symbol for the bullet points in each level of the list.

\section2 Images

Inline images are added to documents through the cursor in the usual manner.
Unlike many other elements, all of the image properties are specified by the
image's format. This means that a QTextImageFormat object has to be
created before an image can be inserted:

\snippet doc/src/snippets/textdocument-images/main.cpp 1

The image name refers to an entry in the application's resource file.
The method used to derive this name is described in
\l{resources.html}{The Qt Resource System}.

*/

/*!
\page richtext-common-tasks.html
\contentspage richtext.html Contents
\previouspage The QTextCursor Interface
\nextpage Advanced Rich Text Processing

\title Common Rich Text Editing Tasks

\tableofcontents

There are a number of tasks that are often performed by developers
when editing and processing text documents using Qt. These include the use
of display widgets such as QTextBrowser and QTextEdit, creation of
documents with QTextDocument, editing using a QTextCursor, and
exporting the document structure.
This document outlines some of the more common ways of using the rich
text classes to perform these tasks, showing convenient patterns that can
be reused in your own applications.

\section1 Using QTextEdit

A text editor widget can be constructed and used to display HTML in the
following way:

\snippet doc/src/snippets/code/doc_src_richtext.qdoc 2

By default, the text editor contains a document with a root frame, inside
which is an empty text block. This document can be obtained so that it can
be modified directly by the application:

\snippet doc/src/snippets/code/doc_src_richtext.qdoc 3

The text editor's cursor may also be used to edit a document:

\snippet doc/src/snippets/code/doc_src_richtext.qdoc 4

Although a document can be edited using many cursors at once, a QTextEdit
only displays a single cursor at a time. Therefore, if we want to update the
editor to display a particular cursor or its selection, we need to set the
editor's cursor after we have modified the document:

\snippet doc/src/snippets/code/doc_src_richtext.qdoc 5

\section1 Selecting Text

Text is selected by moving the cursor using operations that are similar to
those performed by a user in a text editor. To select text between two
points in the document, we need to position the cursor at the first point
then move it using a special mode (\l{QTextCursor::MoveMode}) with a
move operation (\l{QTextCursor::MoveOperation}).
When we select the text, we leave the selection anchor at the old cursor
position just as the user might do by holding down the Shift key when
selecting text:

\snippet doc/src/snippets/textdocument-selections/mainwindow.cpp 1

In the above code, a whole word is selected using this method. QTextCursor
provides a number of common move operations for selecting individual
characters, words, lines, and whole blocks.

\section1 Finding Text

QTextDocument provides a cursor-based interface for searching, making
it easy to find and modify text in the style of a text editor. The following
code finds all the instances of a particular word in a document, and changes
the color of each:

\snippet doc/src/snippets/textdocument-find/main.cpp 0
\snippet doc/src/snippets/textdocument-find/main.cpp 1

Note that the cursor does not have to be moved after each search and replace
operation; it is always positioned at the end of the word that was just
replaced.

\section1 Printing Documents

QTextEdit is designed for the display of large rich text documents that are
read on screen, rendering them in the same way as a web browser. As a result,
it does not automatically break the contents of the document into page-sized
pieces that are suitable for printing.

QTextDocument provides a \l{QTextDocument::print()}{print()} function to
allow documents to be printed using the QPrinter class. The following code
shows how to prepare a document in a QTextEdit for printing with a QPrinter:

\snippet doc/src/snippets/textdocument-printing/mainwindow.cpp 0

The document is obtained from the text editor, and a QPrinter is constructed
then configured using a QPrintDialog. If the user accepts the printer's
configuration then the document is formatted and printed using the
\l{QTextDocument::print()}{print()} function.

*/

/*!
\page richtext-advanced-processing.html
\contentspage richtext.html Contents
\previouspage Common Rich Text Editing Tasks
\nextpage Supported HTML Subset

\title Advanced Rich Text Processing

\section1 Handling Large Files

Qt does not limit the size of files that are used for text
processing.  In most cases, this will not present a problem. For
especially large files, however, you might experience that your
application will become unresponsive or that you will run out of
memory. The size of the files you can load depends on your
hardware and on Qt's and your own application's implementation.

If you are faced with this problem, we recommend that you address the
following issues:

\list
    \o You should consider breaking up large paragraphs into smaller 
       ones as Qt handles small paragraphs better. You could also 
       insert line breaks at regular intervals, which will look the
       same as one large paragraph in a QTextEdit.
    \o You can reduce the amount of blocks in a QTextDocument with 
       \l{QTextDocument::}{maximumBlockCount()}. The document is only
       as large as the number of blocks as far as QTextEdit is concerned.
    \o When adding text to a text edit, it is an advantage to add it 
       in an edit block (see example below). The result is that the
       text edit does not need to build the entire document structure at once.
\endlist

We give an example of the latter technique from the list. We assume that
the text edit is visible.

\snippet doc/src/snippets/code/doc_src_richtext.qdoc 6

\omit
Ideas for other sections:

 * Hiding QTextBlock elements.
 * Changing the word wrapping mode in QTextEdit. Custom word wrapping?
\endomit
*/

/*!
    \page richtext-html-subset.html
    \title Supported HTML Subset
    \brief Describes the support for HTML markup in text widgets.

    \contentspage richtext.html Contents
    \previouspage Common Rich Text Editing Tasks

    Qt's text widgets are able to display rich text, specified using a subset of \l{HTML 4}
    markup. Widgets that use QTextDocument, such as QLabel, QTextEdit, QTreeWidgetItem and
    the other item widgets, are able to display rich text specified in this way.

    \tableofcontents

    \section1 Using HTML Markup in Text Widgets

    Widgets automatically detect HTML markup and display rich text accordingly. For example,
    setting a label's \l{QLabel::}{text} property with the string \c{"<b>Hello</b> <i>Qt!</i>"}
    will result in the label displaying text like this: \bold{Hello} \e{Qt!}

    When HTML markup is used for text, Qt follows the rules defined by the \l{HTML 4}
    specification. This includes default properties for text layout, such as the
    direction of the text flow (left-to-right) which can be changed by applying the
    \l{#Block Attributes}{\c dir} attribute to blocks of text.

    \section1 Supported Tags

    The following table lists the HTML tags supported by Qt's
    \l{Rich Text Processing}{rich text} engine:

    \table
    \header \o Tag
            \o Description
            \o Comment
    \row    \o \c a
            \o Anchor or link
            \o Supports the \c href and \c name attributes.
    \row    \o \c address
            \o Address
            \o
    \row    \o \c b
            \o Bold
            \o
    \row    \o \c big
            \o Larger font
            \o
    \row    \o \c blockquote
            \o Indented paragraph
            \o
    \row    \o \c body
            \o Document body
            \o Supports the \c bgcolor attribute, which
               can be a Qt \l{QColor::setNamedColor()}{color name}
               or a \c #RRGGBB color specification.
    \row    \o \c br
            \o Line break
            \o
    \row    \o \c center
            \o Centered paragraph
            \o
    \row    \o \c cite
            \o Inline citation
            \o Same as \c i.
    \row    \o \c code
            \o Code
            \o Same as \c tt.
    \row    \o \c dd
            \o Definition data
            \o
    \row    \o \c dfn
            \o Definition
            \o Same as \c i.
    \row    \o \c div
            \o Document division
            \o Supports the standard \l{block attributes}.
    \row    \o \c dl
            \o Definition list
            \o Supports the standard \l{block attributes}.
    \row    \o \c dt
            \o Definition term
            \o Supports the standard \l{block attributes}.
    \row    \o \c em
            \o Emphasized
            \o Same as \c i.
    \row    \o \c font
            \o Font size, family, and/or color
            \o Supports the following attributes:
               \c size, \c face, and \c color (Qt
               \l{QColor::setNamedColor()}{color names} or
               \c #RRGGBB).
    \row    \o \c h1
            \o Level 1 heading
            \o Supports the standard \l{block attributes}.
    \row    \o \c h2
            \o Level 2 heading
            \o Supports the standard \l{block attributes}.
    \row    \o \c h3
            \o Level 3 heading
            \o Supports the standard \l{block attributes}.
    \row    \o \c h4
            \o Level 4 heading
            \o Supports the standard \l{block attributes}.
    \row    \o \c h5
            \o Level 5 heading
            \o Supports the standard \l{block attributes}.
    \row    \o \c h6
            \o Level 6 heading
            \o Supports the standard \l{block attributes}.
    \row    \o \c head
            \o Document header
            \o
    \row    \o \c hr
            \o Horizontal line
            \o Supports the \c width attribute, which can
               be specified as an absolute or relative (\c %) value.
    \row    \o \c html
            \o HTML document
            \o
    \row    \o \c i
            \o Italic
            \o
    \row    \o \c img
            \o Image
            \o Supports the \c src, \c source
               (for Qt 3 compatibility), \c width, and \c height
               attributes.
    \row    \o \c kbd
            \o User-entered text
            \o
    \row    \o \c meta
            \o Meta-information
            \o If a text encoding is specified using the \c{meta} tag,
               it is picked up by Qt::codecForHtml().
               Likewise, if an encoding is specified to
               QTextDocument::toHtml(), the encoding is stored using
               a \c meta tag, for example:

    \snippet doc/src/snippets/code/doc_src_richtext.qdoc 7

    \row    \o \c li
            \o List item
            \o
    \row    \o \c nobr
            \o Non-breakable text
            \o
    \row    \o \c ol
            \o Ordered list
            \o Supports the standard \l{list attributes}.
    \row    \o \c p
            \o Paragraph
            \o Left-aligned by default. Supports the standard
               \l{block attributes}.
    \row    \o \c pre
            \o Preformated text
            \o
    \row    \o \c qt
            \o Qt rich-text document
            \o Synonym for \c html. Provided for compatibility with
               earlier versions of Qt.
    \row    \o \c s
            \o Strikethrough
            \o
    \row    \o \c samp
            \o Sample code
            \o Same as \c tt.
    \row    \o \c small
            \o Small font
            \o
    \row    \o \c span
            \o Grouped elements
            \o
    \row    \o \c strong
            \o Strong
            \o Same as \c b.
    \row    \o \c sub
            \o Subscript
            \o
    \row    \o \c sup
            \o Superscript
            \o
    \row    \o \c table
            \o Table
            \o Supports the following attributes: \c border,
               \c bgcolor (Qt \l{QColor::setNamedColor()}{color names}
               or \c #RRGGBB), \c cellspacing, \c cellpadding,
               \c width (absolute or relative), and \c height.
    \row    \o \c tbody
            \o Table body
            \o Does nothing.
    \row    \o \c td
            \o Table data cell
            \o Supports the standard \l{table cell attributes}.
    \row    \o \c tfoot
            \o Table footer
            \o Does nothing.
    \row    \o \c th
            \o Table header cell
            \o Supports the standard \l{table cell attributes}.
    \row    \o \c thead
            \o Table header
            \o If the \c thead tag is specified, it is used when printing tables
               that span multiple pages.
    \row    \o \c title
            \o Document title
            \o The value specified using the \c
               title tag is available through
               QTextDocument::metaInformation().
    \row    \o \c tr
            \o Table row
            \o Supports the \c bgcolor attribute, which
               can be a Qt \l{QColor::setNamedColor()}{color name}
               or a \c #RRGGBB color specification.
    \row    \o \c tt
            \o Typewrite font
            \o
    \row    \o \c u
            \o Underlined
            \o
    \row    \o \c ul
            \o Unordered list
            \o Supports the standard \l{list attributes}.
    \row    \o \c var
            \o Variable
            \o Same as \c i.
    \endtable

    \section1 Block Attributes

    The following attributes are supported by the \c div, \c dl, \c
    dt, \c h1, \c h2, \c h3, \c h4, \c h5, \c h6, \c p tags:

    \list
    \o \c align (\c left, \c right, \c center, \c justify)
    \o \c dir (\c ltr, \c rtl)
    \endlist

    \section1 List Attributes

    The following attribute is supported by the \c ol and \c ul tags:

    \list
    \o \c type (\c 1, \c a, \c A, \c square, \c disc, \c circle)
    \endlist

    \section1 Table Cell Attributes

    The following attributes are supported by the \c td and \c th
    tags:

    \list
    \o \c width (absolute, relative, or no-value)
    \o \c bgcolor (Qt \l{QColor::setNamedColor()}{color names} or \c #RRGGBB)
    \o \c colspan
    \o \c rowspan
    \o \c align (\c left, \c right, \c center, \c justify)
    \o \c valign (\c top, \c middle, \c bottom)
    \endlist

    \section1 CSS Properties
    The following table lists the CSS properties supported by Qt's
    \l{Rich Text Processing}{rich text} engine:

    \table
    \header \o Property
            \o Values
            \o Description
    \row
            \o \c background-color
            \o <color>
            \o Background color for elements
    \row
            \o \c background-image
            \o <uri>
            \o Background image for elements
    \row    \o \c color
            \o <color>
            \o Text foreground color
    \row    \o \c font-family
            \o <family name>
            \o Font family name
    \row    \o \c font-size
            \o [ small | medium | large | x-large | xx-large ] | <size>pt | <size>px
            \o Font size relative to the document font, or specified in points or pixels
    \row    \o \c font-style
            \o [ normal | italic | oblique ]
            \o
    \row    \o \c font-weight
            \o [ normal | bold | 100 | 200 | 300 | 400 | 500 | 600 | 700 | 800 | 900 ]
            \o Specifies the font weight used for text, where \c normal and \c bold
               are mapped to the corresponding QFont weights. Numeric values are
               8 times the equivalent QFont weight values.
    \row    \o \c text-decoration
            \o none | [ underline || overline || line-through ]
            \o Additional text effects
    \row    \o \c font
            \o [ [ <'font-style'> || <'font-weight'> ]? <'font-size'> <'font-family'> ]
            \o Font shorthand property
    \row    \o \c text-indent
            \o <length>px
            \o First line text indentation in pixels
    \row    \o \c white-space
            \o normal | pre | nowrap | pre-wrap
            \o Declares how whitespace in HTML is handled.
    \row    \o \c margin-top
            \o <length>px
            \o Top paragraph margin in pixels
    \row    \o \c margin-bottom
            \o <length>px
            \o Bottom paragraph margin in pixels
    \row    \o \c margin-left
            \o <length>px
            \o Left paragraph margin in pixels
    \row    \o \c margin-right
            \o <length>px
            \o Right paragraph margin in pixels
    \row    \o \c padding-top
            \o <length>px
            \o Top table cell padding in pixels
    \row    \o \c padding-bottom
            \o <length>px
            \o Bottom table cell padding in pixels
    \row    \o \c padding-left
            \o <length>px
            \o Left table cell padding in pixels
    \row    \o \c padding-right
            \o <length>px
            \o Right table cell padding in pixels
    \row    \o \c padding
            \o <length>px
            \o Shorthand for setting all the padding properties at once.
    \row    \o \c vertical-align
            \o baseline | sub | super | middle | top | bottom
            \o Vertical text alignment. For vertical alignment in text table cells only middle, top, and bottom apply.
    \row    \o \c border-color
            \o <color>
            \o Border color for text tables.
    \row    \o \c border-style
            \o none | dotted | dashed | dot-dash | dot-dot-dash | solid | double | groove | ridge | inset | outset
            \o Border style for text tables.
    \row    \o \c background
            \o [ <'background-color'> || <'background-image'> ]
            \o Background shorthand property
    \row    \o \c page-break-before
            \o [ auto | always ]
            \o Make it possible to enforce a page break before the paragraph/table
    \row    \o \c page-break-after
            \o [ auto | always ]
            \o Make it possible to enforce a page break after the paragraph/table
    \row    \o float
            \o [ left | right | none ]
            \o Specifies where an image or a text will be placed in another element. Note that the \c float property is
               only supported for tables and images.
    \row    \o \c text-transform
            \o [ uppercase | lowercase | smallcaps ]
            \o Select the transformation that will be performed on the text prior to displaying it.
    \row    \o \c word-spacing
            \o <width>px
            \o Specifies an alternate spacing between each word.
    \endtable

    \section1 Supported CSS Selectors

    All CSS 2.1 selector classes are supported except pseudo-class selectors such
    as \c{:first-child}, \c{:visited} and \c{:hover}.

*/