[Area] Expressions [Report Designer] Write expressions in Visual Basic. The expression editor provides IntelliSense syntax support. Use the Output window to view warnings and compile-time error messages. Add references to .NET Framework assemblies or to custom assemblies that contain your custom code. [Report Builder 3.0] 
Use default expressions to display, group, and sort data in the report. You can write expressions in Microsoft Visual Basic, but there are fewer options for debugging than in Report Designer.