CellGroup

CellGroup[{cell₁, cell₂, ...}]
gives an open group of cells that can appear in a Mathematica notebook.

CellGroup[{cell₁, cell₂, ...}, 1]
gives a cell group in which only the first cell is open.

CellGroup[{cell₁, cell₂, ...}, -1]
gives a cell group in which only the last cell is open.

CellGroup[{cell₁, cell₂, ...}, {i₁, i₂, ...}]
gives a cell group in which cells i₁, i₂, ... are open.

A CellGroup object can be inserted in its entirety into a notebook using CellPrint.

Cell grouping specified by CellGroup will be overridden by automatic grouping in a notebook unless CellGrouping->Manual is set.

If any cell_i is a string or Text object, it will be wrapped with TextCell. If it is any other type of expression, it will be wrapped with ExpressionCell.