The ConnectionStringsExpressionBuilder.SupportsEvaluate property indicates whether the ConnectionStringsExpressionBuilder.EvaluateExpression(object, System.Web.UI.BoundPropertyEntry, object, ExpressionBuilderContext) method has been implemented in the class. ConnectionStringsExpressionBuilder.EvaluateExpression(object, System.Web.UI.BoundPropertyEntry, object, ExpressionBuilderContext) must be implemented within an expression builder for an expression to be evaluated in a page that is not compiled. System.Web.Compilation.ConnectionStringsExpressionBuilder supports no-compile evaluation of connection strings, so true is always returned.