QQuickItem documentation should mention the expected behaviour of derived classes

When deriving classes from QQuickItem there are a number of virtual methods that can be overridden (e.g. geometryChanged). The documentation should be a bit clearer about what derived classes should do. For example, one of the following snippets:

1) Derived classes should call the base class method before/after their own implementation
2) This method is called as a convenience for derived classes (hmm, why not a signal)
3) This method must be implemented by derived classes (why not a pure?)

In the specific case of geometryChanged it suggests #2 when it's really #1.