The appearance of each cell is defined by one or more XLStyle objects.
When displaying a cell, Excel combines the row, column, and cell styles and merges the style elements defined in each one in order to determine how the cell should be displayed.
The precedence of the styles is: (1) cell, (2) row, (3) column, (4) default style. For example, if a cell style defines the font and background color, those will be applied regardless of the settings in the row and column styles. If the row style defines an alignment, that will be applied regardless of the column style, and so on.
The cell style may be null, in which case the cell is displayed using the other styles available or the default book style if no others are available.
