A flag indicating that directory rights should be inherited from the capability declaration
if they were not present in an expose or offer declaration.
The subdirectory inside of the storage backing directory’s subdirectory to
use, if any. The difference between this and SubDir is that a) the SubDir
generically refers to the subdirectory of a directory capability, and b) the
SubDir is appended to the IsolatedStoragePath first (which is a path into a
backing directory), and component_manager will create the StorageSubdir if
it doesn’t exist but won’t create SubDir. Accordingly, the complete path to
a storage capability within the backing directory is
{IsolatedStoragePath}/{SubDir}/{StorageSubdir}.