This is what I am doing now:
Log.Logger = new LoggerConfiguration()
.ReadFrom.AppSettings()
.WriteTo.Logger(l => l.Filter.ByIncludingOnly(Matching.WithProperty("XXX")).WriteTo.File("output.txt"))
.CreateLogger();
I have my main Logger set up in app.config, but I can't figure out the syntax for specifying a sub-logger there. I'd really like to avoid mixing code and appSettings configuration.