Really just a minor thing, but quite confusing:

Having this appender defined in my logback.groovy:

appender("CONSOLE", ConsoleAppender) {
target = 'SystemErr'
...
}

I got this warning from logback:

Main: 13:44:44,338 + WARN in ch.qos.logback.core.ConsoleAppender[CONSOLE] - [SystemErr] should be one of [SystemOut, SystemErr]
Main: 13:44:44,338 |-WARN in ch.qos.logback.core.ConsoleAppender[CONSOLE] - Using previously set target, System.out by default.

Well, looking at that warning I could not see what I had done wrong.

Would be nice if that warning can be fixed to print the actual two possible options.