Fix documentation for QML_ATTACHED and QML_FOREIGN

They can in fact not be combined.

Pick-to: 6.2
Change-Id: Ic01edf9328d7235511f305ed15114360b79d0a36
Reviewed-by: Fabian Kosmale <fabian.kosmale@qt.io>
(cherry picked from commit 5a86636)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>
(cherry picked from commit 8bd24a7)
(cherry picked from commit f48bc12)

Author: Ulf Hermann

src/qml/doc/src/qmlfunctions.qdoc

@@ -455,7 +455,7 @@
   Declares that any \l QML_ELEMENT, \l QML_NAMED_ELEMENT(), \l QML_ANONYMOUS,
   \l QML_INTERFACE, \l QML_UNCREATABLE(), \l QML_SINGLETON,
   \l QML_ADDED_IN_MINOR_VERSION(), \l QML_REMOVED_IN_MINOR_VERSION(),
-  \l QML_ATTACHED(), \l QML_EXTENDED(), or \l  QML_EXTENDED_NAMESPACE() macros
+  \l QML_EXTENDED(), or \l  QML_EXTENDED_NAMESPACE() macros
   in the enclosing C++ type do not apply to the enclosing type but instead to
   \a FOREIGN_TYPE. The enclosing type still needs to be registered with the
   \l {The Meta-Object System}{meta object system} using a \l Q_GADGET or
@@ -469,6 +469,9 @@
   the element will be named like the struct it is contained in, not the foreign type.
   See the \l {Extension Objects} for an example.
 
+  \note QML_ATTACHED() can currently not be redirected like this. It has to be
+  specificed in the same type that implements qmlAttachedProperties().
+
   \include {qualified-class-name.qdocinc} {class name must be qualified}
 
   \sa QML_ELEMENT, QML_NAMED_ELEMENT(), QML_FOREIGN_NAMESPACE()