It would be useful to be able to trigger a script "onChange" of a visualization in order to synchronize visualizations when the axis selector of one visualization is changed. While most of this can also be achieved using a central property
a) sometime we don't want to have a property in a separate TextArea
b) property controls don't work as nicely with hierarchies as the selector-slider (it requires more manual work on the part of the property).
That way I can change the hierarchy-setting on one viz and automatically have other viz use the same hierarchy level.