Parameters
- firstCells
- The first cells.
- secondCells
- The second cells.
Return Value
A CellReferences instance that contains both of the two CellReferences that form the union.
Target Platforms: .NET 10; .NET 9; .NET 8; .NET 7; .NET 6; .NET Framework 4.8, 4.7, 4.6, 4.5, 4.0, 3.5