[news.eclipse.platform.swt] Class cast from ISelection to IStructuredSel

[Christoph Czernohous <cc@xxxxxxxxxx>]

Hello,

When contributing to a popup menu extension point with an object 
contribution, method IObjectActionDelegate.selectionChanged(IAction 
action, ISelection selection) is called every time the user selects or 
deselects an item in the visible part.

My question is how to identify the item on which the popup menu was 
invoked. I know that in case of a tree, I can do a class cast from 
ISelection to IStructuredSelection and get it from there.
The point is I cannot find any documentation that this class cast is 
valid. Can someone point me to the right place in the documentation?

Thanks

Christoph