anchor.diff:  === Best Practices for Command Line Interfaces
   
   When designing your command line application,
  -the https://www.gnu.org/prep/standards/html_node/Command_002dLine-Interfaces.html#Command_002dLine-Interfaces[GNU recommendations] for command line interfaces and http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap12.html#tag_12_02[POSIX Utility Guidelines] may be useful. Generally, many applications use options for optional values and parameters for mandatory values.
  +the https://www.gnu.org/prep/standards/html_node/Command_002dLine-Interfaces.html#Command_002dLine-Interfaces[GNU recommendations] for command line interfaces and http://pubs.opengroup.org/onlinepubs/9699919799/basedefs/V1_chap12.html#tag_12_02[POSIX Utility Guidelines] may be useful.
  +
  +Generally, many applications use options for optional values and parameters for mandatory values.
   However, picocli lets you make options required if you want to, see <<Required Arguments>>.
   
   
  
positive.code: = picocli - a mighty tiny Command Line Interface
  :author: Remko Popma
  :email: rpopma@apache.org
  :revnumber: 0.9.5-SNAPSHOT
  :revdate: 2017-05-04
  :toc: left
  :numbered:
  :toclevels: 2
  
negative.code: It is the responsibility of the application to check the field and show the usage help message:
  [source,java]
  ----
  App app = CommandLine.parse(new App(), args);
  if (app.helpRequested) {
     CommandLine.usage(new App(), System.err);
     return;
  