ColSpan & RowSpan for custom items

Would like to have a multi-column poly list, with expandable sections. However at the moment the expandable item is treated as other items and squeezed into a single cell space.

What I would like to see is the ability for an item (in this case the expandable section) to be drawn across the columns for a poly list - in effect having its own row. Then the expanding would act on the items below and would look better than it currently does.

This feature was implemented.