With the default setting CellLabelPositioning -> Automatic, the label for a cell is placed to the left of the cell if it is short enough to fit in the left margin. Otherwise, the label is placed above the cell.
With the setting CellLabelPositioning->Left, the label for a cell is placed to the left of the cell at the level of the first line.
With the setting CellLabelPositioning->Above, the label for a cell is placed above the cell starting from the left edge of the page.
