public override string ToString()
{
if( this == LogFilter.Undefined ) return "Undefined";
if( this == LogFilter.Debug ) return "Debug";
if( this == LogFilter.Verbose ) return "Verbose";
if( this == LogFilter.Monitor ) return "Monitor";
if( this == LogFilter.Terse ) return "Terse";
if( this == LogFilter.Release ) return "Release";
if( this == LogFilter.Off ) return "Off";
if( this == LogFilter.Invalid ) return "Invalid";
return String.Format( "{{{0},{1}}}", Group, Line );
}