Result returned by list().
Objects in this directory. You can call getMetadate() and getDownloadUrl() on them.
If set, there might be more results for this list. Use this token to resume the list.
References to prefixes (sub-folders). You can call list() on them to get its contents.
Folders are implicit based on '/' in the object paths. For example, if a bucket has two objects '/a/b/1' and '/a/b/2', list('/a') will return '/a/b' as a prefix.