Besides the interfaces that are dedicated to each of the specific models, there are also optional interfaces that provide additional support and may be used when making custom models. These optional interfaces and the customizations they allow are summarized in this table:

Optional Interface	Customizations Allowed
IArraySupport	Allows customization of support for getting and setting arrays of values in a range of cells
IDataSourceSupport	Allows customization of data binding on a sheet
IChildModelSupport	Allows customization of hierarchical data models for hierarchies on a sheet; used in conjunction with IDataSourceSupport
ICalculationSupport, IIterationSupport	Allows recalculation of formulas in the cells in the data model. Allows recursive formulas(with circular references) in the data model.
IDisjointSelections, IQuerySelection	Allows customization of an ordered array of cell ranges containing the selected cells with the minimal overlap between the ranges on a sheet
INamedStyle, IParseFormatSupport	Allows customization of collections of custom styles in the style model
INonEmptyCells	Allows customization of non-empty counts to find out which rows or columns have data in the cells of that row or column on a sheet
IOptimizedEnumerationSupport, IOptimizedEnumerationSupport2	Allows customization of optimized enumeration for iterating to the next non-empty row or column on a sheet
IUnboundRowSupport	Allows customization of unbound rows with data binding on a sheet; used in conjunction with IDataSourceSupport

None of these optional interfaces are required for saving Excel or text files, or for printing. For more detailed information on these interfaces, refer to the FarPoint.Win.Spread.Model namespace in the Assembly Reference.

For more information on formulas in cells, refer Managing Formulas in Cells.