docs: function setOutput(output) {
           if (!output ||
               typeof output.log !== 'function') {
               throw Error('logger.setOutput: expect an object as the parameter with "log" and "error" properties.');
           }
           outputFunctions = {
               log: output.log,
               error: (typeof output.error === 'function') ? output.error : output.log
           };
       }