anchor.diff:  }
   ----
   
  +.Kotlin
  +[source,kotlin,role="secondary"]
  +----
  +val example = MutuallyExclusiveOptionsDemo()
  +val cmd = CommandLine(example)
  +
  +try {
  +    cmd.parseArgs("-a=1", "-b=2")
  +} catch (ex: MutuallyExclusiveArgsException) {
  +    assert("Error: -a=<a>, -b=<b> are mutually exclusive (specify only one)" == ex.message)
  +}
  +----
  +
   For the above group, only one of the options can be specified. Any other combination of options, or the absence of options, is invalid.
   
   CAUTION: Picocli will not initialize the `@ArgGroup`-annotated field
  
positive.code:     static class Section2 {
          @Option(names = "-x", description = "Option X") int x;
          @Option(names = "-y", description = "Option Y") int y;
          @Option(names = "-z", description = "Option X") int z;
      }
  
      public static void main(String[] args) {
          new CommandLine(new OptionSectionDemo()).usage(System.out);
      }
  }
  ----
  
  
negative.code:     var y = 0
  
      @Spec lateinit var spec: CommandSpec
  
      override fun run() {
          val pr: ParseResult = spec.commandLine().parseResult
  
  