Terminology

Status: Current. Reference for users and maintainers.

Use these names consistently when discussing Allors Excel, in prose, code comments, diagrams and pull requests. Exact identifiers keep their declared spelling. The linked pages own the definitions.

The parts

Term	Definition and usage
Program	The class that implements IProgram: the add-in’s logic, which receives the lifecycle callbacks and works with the virtual workbook. Say program for the class and the add-in for the whole. How the virtual workbook works describes the callbacks.
Add-in	The IAddIn: the root object that holds the workbooks, the ribbon and the program. In Excel it is created by the host; headless it is created directly.
Host	The code that loads inside Excel and creates the add-in: an Excel-DNA ribbon or a VSTO ThisAddIn. Build an Excel add-in describes both.
Ribbon	The IRibbon: the host’s ribbon, which the program asks to Invalidate so that Excel queries its callbacks again.
Virtual workbook	The IWorkbook, IWorksheet, ICell, IRow and IColumn objects, which the program reads and writes. Say workbook, worksheet and cell for them; say Excel’s workbook or the interop workbook for the COM objects behind them.
Coordinates	A cell’s row and column, both zero-based, as in sheet[0, 0] for A1. Excel’s own indexes and A1 names are one-based; the Index of a worksheet is Excel’s one-based index.
Range	An Allors.Excel.Range: a zero-based row and column, optional counts, an optional worksheet and an optional name. Not Excel’s Range object, which the interop implementation calls an interop range.
Named range	An Excel name that refers to a range, scoped to the workbook or to a worksheet.
Options	A cell’s Options: a range whose values are offered as the cell’s list validation.

Writing and reading

Term	Definition and usage
Dirty	A cell or row whose change has not been written to Excel yet. Setting a value, formula, comment, style, number format, options or the hidden state marks it dirty.
Flush	IWorksheet.Flush(): writing every dirty change of a worksheet to Excel in blocks. Say that a worksheet is flushed; the implementation’s methods are called Render…, but render is not used in prose.
Chunk	A rectangular block of adjacent dirty cells that the interop implementation writes with one COM call.
Change event	CellsChanged and SheetChanged: raised by a worksheet with the cells whose values Excel reported as changed.
Value converter	An IValueConverter that turns the value Excel reports into the value the cell keeps; DefaultValueConverter uses the cell’s previous value to choose a conversion. Value conversion describes its rules and limits.
Binding	A Binding registered with a Binder: how a cell’s value is produced from the model and, for a two-way binding, how an edit goes back to the model. See Bind cells to your model.
Existential attribute	IAddIn.ExistentialAttribute: the name of a custom document property; when set, the interop add-in tracks only workbooks that have that property.

Implementations

Term	Definition and usage
Headless	The Allors.Excel.Headless implementation: the workbook kept in memory, without Excel, for tests and tools.
Interop	The Allors.Excel.Interop implementation: the workbook backed by Excel’s COM objects through the primary interop assemblies.
Excel-DNA	The Excel-DNA add-in framework, used by the Allors.Excel.Interop.Dna host.
VSTO	Visual Studio Tools for Office, used by the Allors.Excel.Interop.Vsto host.