[NONE] Throw exception when null operations are added to a composite operation.
[NONE] Split ContentPolicy#deleteContent() into smaller chunks.
[NONE] Unestablish anchor relations first, when deleting multiple parts at once.
[NONE] Use ContentPolicy to change curve anchorages in the example.
[NONE] Return null when a content part has no adapter and no model.
[NONE] Fix visual part registration.
[NONE] Fix changing content anchorages within the example.
[NONE] Add sysouts (commented out) to operations for debugging purposes.
[NONE] Clear interaction models within FXDeleteSelectedOnTypePolicy.
[NONE] Extract method for better extensibility.
[NONE] Use DeletionPolicy within FXDeleteSelectedOnTypePolicy.
[445846] Implement CreationPolicy and FXExampleCreateShapeOnClickPolicy.

The CreationPolicy is the pendant to the DeletionPolicy.
[NONE] Chain clearing the interaction models after deletion within the example.
[NONE] Make example colors and shapes accessible.
[445846] Create handle shape instead of magenta rectangle.
[NONE] Introduce FXBlendImageView and use it for the hover handles.

The FXBlendImageView can be used to display different images depending on
whether the mouse hovers the image view, or not. The images are exchanged with
a blend effect.
[NONE] Add null-checks for operations within ContentPolicy.
[445846] Center newly created handle shape at pointer location.
[445846] Add index parameter when adding/removing content children.

This fixes the z-ordering of the children when undoing a remove operation.
[NONE] Do not throw an exception when no DeletionPolicy is registered.