Filter       func(info FileInfo) bool // return WalkFilter returns 'true/false'
	Marker       string                   // set to skip until this object
	LatestOnly   bool                     // returns only latest versions for all matching objects
	AskDisks     string                   // dictates how many disks are being listed
	VersionsSort WalkVersionsSortOrder    // sort order for versions of the same object; default: Ascending order in ModTime