One should be able to cancel the detail expand or collapse events of the grids by providing a Expanding / Collapsing event.

One use case for this that would be way easier to implement is when one is using a detail template to edit some form of data related to the expanded row but not bound to it's data item, instead bound to specific data coming from other source.

If when you expand another row the previously expanded one gets collapsed I would like to be able to prevent that on those events to check for changes, challenge the user and act accordingly.