Register a positional argument.
Register a final positional argument that collects all remaining tokens.
Register a command (spec section 1.7) and return it, to register its options and arguments on.
At most one of these options may be given.
At least one of these options must be given.
Register a repeatable option whose values accumulate into a list.
Declare an external command the program needs.
When lng is given, the others must be too.
option holds the config file path; prefixes is comma-separated.
Base for command-line path values (default: the working directory).
Set the help description and return this CLI.
What running the program does: read-only, idempotent, destructive, network.
The environment to read (default: the process environment).
Set the final help text and return this CLI.
Fallback directories (colon-separated, relative to the root) for bare relative values of a path option.
Base for default path values (default: the working directory); relative to the working directory.
What the program reads on stdin; contentType is a MIME type or a comma-separated list.
What the program writes on stdout; undeclared means text.