[Interest] QAbstractItemModel::layoutAboutToBeChanged

[Bill Crocker]

Gang:

The doc for QAbstractItemModel::layoutAboutToBeChanged() says...

     This signal is emitted just before the layout of a model is changed.
     Components connected to this signal use it to adapt to changes in the 
model's layout.

What is the "layout of a model" and how does that differ from
adding and removing rows and columns.

Thanks.

Bill