Restore extension types documentation

The documentation on QML extension types was accidentally removed on the
big restructuring of commit 28def0bdd084989c17a157e0c4ab80c259081caa.
This restores it to a section on the "Defining QML Types from C++" page
mostly unchanged, and makes the source of the example that was already
there visible.

The reference documentation of the qmlRegisterExtendedType is added as
well, and the one for qmlRegisterExtendedUncreatableType and
qmlRegisterCustomExtendedType that was added in
fcb40ff6d71f4561401e6b2bd4d7fc706fff8eee is now fixed. It was not being
generated because referred to "QQmlEgine" instead of "QQmlEngine".

Change-Id: I1403b10076c64a4c0d760f72b06dd52c38b351a5
Reviewed-by: Paul Lemire <paul.lemire@kdab.com>
Reviewed-by: Simon Hausmann <simon.hausmann@digia.com>

3 files changed, 85 insertions, 3 deletions

diff --git a/examples/qml/doc/src/qml-extending.qdoc b/examples/qml/doc/src/qml-extending.qdoc
index 8f44e4f506..f25b75ed29 100644
--- a/examples/qml/doc/src/qml-extending.qdoc
+++ b/examples/qml/doc/src/qml-extending.qdoc
@@ -63,6 +63,25 @@ loads and runs the QML snippet shown at the beginning of this page.
 */
 
 /*!
+\example referenceexamples/extended
+\title Extending QML - Extension Objects Example
+\brief Extension Objects
+\ingroup qmlextendingexamples
+
+This example builds on:
+\list
+\li \l {Extending QML - Adding Types Example}
+\endlist
+
+Shows how to use \l qmlRegisterExtendedType() to provide an \l {Registering
+Extension Objects}{extension object} to a \l QLineEdit without modifying or
+subclassing. The QML engine instantiates a \l QLineEdit and sets a property that
+only exists on the extension type. The extension type performs calls on the \l
+QLineEdit that otherwise will not be accessible to the QML engine.
+
+*/
+
+/*!
 \example referenceexamples/properties
 \title Extending QML - Object and List Property Types Example
 \brief Exporting C++ Properties
diff --git a/src/qml/doc/src/cppintegration/definetypes.qdoc b/src/qml/doc/src/cppintegration/definetypes.qdoc
index 03607df2e5..2f780503b2 100644
--- a/src/qml/doc/src/cppintegration/definetypes.qdoc
+++ b/src/qml/doc/src/cppintegration/definetypes.qdoc
@@ -294,6 +294,52 @@ This is useful when deriving from base classes provided by other authors,
 e.g. when extending classes from the Qt Quick module.
 
 
+\section2 Registering Extension Objects
+
+When integrating existing classes and technology into QML, APIs will
+often need tweaking to fit better into the declarative environment.
+Although the best results are usually obtained by modifying the original
+classes directly, if this is either not possible or is complicated by some
+other concerns, extension objects allow limited extension possibilities
+without direct modifications.
+
+\e{Extension objects} add additional properties to an existing type. Extension
+objects can only add properties, not signals or methods. An extended type
+definition allows the programmer to supply an additional type, known as the
+\e{extension type}, when registering the class. The properties are transparently
+merged with the original target class when used from within QML. For example:
+
+\snippet referenceexamples/extended/example.qml 0
+
+The \c leftMargin property is a new property added to an existing C++ type, \l
+QLineEdit, without modifying its source code.
+
+The \l qmlRegisterExtendedType() function is for registering extended types.
+Note that it has two forms.
+
+\code
+template<typename T, typename ExtendedT>
+int qmlRegisterExtendedType(const char *uri, int versionMajor, int versionMinor, const char *qmlName)
+
+template<typename T, typename ExtendedT>
+int qmlRegisterExtendedType()
+\endcode
+
+This functions should be used instead of the regular \c qmlRegisterType()
+variations. The arguments are identical to the corresponding non-extension
+registration functions, except for the ExtendedT parameter which is the type of
+the extension object.
+
+An extension class is a regular QObject, with a constructor that takes a QObject
+pointer. However, the extension class creation is delayed until the first
+extended property is accessed. The extension class is created and the target
+object is passed in as the parent. When the property on the original is
+accessed, the corresponding property on the extension object is used instead.
+
+The \l{Extending QML - Extension Objects Example}{Extension Objects Example}
+demonstrates a usage of extension objects.
+
+
 \section1 Defining QML-Specific Types and Attributes
 
 
diff --git a/src/qml/doc/src/qmlfunctions.qdoc b/src/qml/doc/src/qmlfunctions.qdoc
index e95784dc5c..6b0f9dba10 100644
--- a/src/qml/doc/src/qmlfunctions.qdoc
+++ b/src/qml/doc/src/qmlfunctions.qdoc
@@ -157,8 +157,25 @@
 */
 
 /*!
-  \fn int qmlRegisterExtendedUncreatableType(const char *uri, int versionMajor, int versionMinor, const char *qmlName, const QString& message)
-  \relates QQmlEgine
+  \fn int qmlRegisterExtendedType(const char *uri, int versionMajor, int versionMinor, const char *qmlName)
+  \relates QQmlEngine
+
+  This template function registers the C++ type and its extension object in the
+  QML system with the name \a qmlName in the library imported from \a uri having
+  version number composed from \a versionMajor and \a versionMinor. Properties
+  not available in the main type will be searched for in the extension object.
+
+  Returns the QML type id.
+
+  #include <QtQml> to use this function.
+
+  \sa qmlRegisterType(), {Registering Extension Objects}
+*/
+
+
+/*!
+  \fn int qmlRegisterExtendedUncreatableType(const char *uri, int versionMajor, int versionMinor, const char *qmlName, const QString& reason)
+  \relates QQmlEngine
 
   This template function registers the C++ type and its extension
   in the QML system with the name \a qmlName in the library imported
@@ -180,7 +197,7 @@
 
 /*!
   \fn int qmlRegisterCustomExtendedType(const char *uri, int versionMajor, int versionMinor, const char *qmlName, QQmlCustomParser *parser)
-  \relates QQmlEgine
+  \relates QQmlEngine
 
   This template function registers the C++ type and its extension
   in the QML system with the name \a qmlName in the library imported