Writes trace information to the trace log, including any user-defined categories and trace messages. All warnings appear in the log as red text.
Namespace: System.Web Assembly: System.Web (in system.web.dll)
Every time the Warn method is called, a TraceContext trace message is added to the TraceRecords messages collection, which is accessible when you handle the TraceFinished event. The message is added with its IsWarning property set to true and its ErrorInfo property set to a null reference (Nothing in Visual Basic).