code: func Output(msg string, lvl Lvl, calldepth int, ctx ...interface{}) {
  	root.write(msg, lvl, ctx, calldepth+skipLevel)
  }
docs: // Output is a convenient alias for write, allowing for the modification of
  // the calldepth (number of stack frames to skip).
  // calldepth influences the reported line number of the log message.
  // A calldepth of zero reports the immediate caller of Output.
  // Non-zero calldepth skips as many stack frames.