is a notebook option that specifies how cells in the notebook should be assembled into groups.
- The default setting is typically CellGrouping->Automatic.
- With CellGrouping->Automatic, cells are automatically grouped in a hierarchical way based on their styles.
- With CellGrouping->Manual, cells must be grouped manually, either by setting up explicit CellGroupData expressions, or by using the Group Cells menu item in the notebook front end.
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