flags

type Flag[T any] struct {
	// Whether this flag is inherited by subcommands.
	Persistent bool

	Name         string
	ShortName    optionals.Optional[rune]
	DefaultValue T
	UsageMsg     string

	Required       bool
	Hidden         bool
	DeprecationMsg optionals.Optional[string]

	// If given, then command-line completions will be restricted to filenames
	// having any of the given extensions.
	FilenameExts optionals.Optional[[]string]

	// Whether command-line completions should be restricted to directory names.
	DirNames bool
}