SelectionCreateCell

SelectionCreateCell[notebook]
copies the contents of the current selection in a notebook into a new cell.

SelectionCreateCell[notebook, sel]
sets the current selection after the copy to be as specified by sel.

If the current selection is a cell group, then SelectionCreateCell will create a new cell group.

SelectionCreateCell[notebook, All] sets the current selection to be the whole of the newly created cell.

Select a cell and create a copy beneath it:

Select a cell, create a copy, and leave the new cell contents selected:

New in 3