Adds short option -x.
Adds a callback function.
Adds a parser under this command.
Hides the option in any usage text.
Adds key name used in the usage text.
Adds key and value names used in the usage text.
Allows the argument to appear at most n times.
Requires the option to appear at least n times.
Chanages the option to be optional.
Requires the option to appear at least once.
Adds description in the usage text.
Allows the argument to appear multiple times.
Adds custom validation.
Adds value name used in the usage text.
A monadic commandline options parser.