For example if I have two widgets scrolLWidget and contentWidget::

 QGraphicsWidget *scrollWidget = new QGraphicsWidget();
scrollWidget->setFlag(Qt::ItemClipsChildrenToShape,true);
QGraphicsWidget *contentWidget = new QGraphicsWidget();
We can add any content to this i.etext, icons etc

scrollWidget->setContentWidget(contentWidget); ---->this would also set contentWidget as its child

We dont apply any kind of transformations, scaling etc.We expect a simple "untransformed" rectangular clip.

Lets see how QGraphicsScene handle this:

In QGraphicsScenePrivate::draw(...)
...
 if (itemClipsChildrenToShape) {
     painter->setClipPath(item->shape(), Qt::IntersectClip); 
    }
...