How to customize the QML type Scene3D in Qt3D from C++?

[UniversE]

I want to customize Scene3D in Qt3D from C++ and use it in QML, then found it instantiates Qt3DRender::Scene3DItem, but the header which declares it warns that:

//
//  W A R N I N G
//  -------------
//
// This file is not part of the Qt API.  It exists purely as an
// implementation detail.  This header file may change from version to
// version without notice, or even be removed.
//
// We mean it.
//

Should I create a class which inherits Qt3DRender::Scene3DItem still or there's another better way?

P.S. I have posted the question on SO, but get no answers till now.