> An application can request temporary or persistent storage space. Temporary storage may be easier to get, at the UA's discretion [looser quota restrictions, available without prompting the user], but the data stored there may be deleted at the UA's convenience, e.g. to deal with a shortage of disk space.
> Conversely, once persistent storage has been granted, data stored there by the application should not be deleted by the UA without user intervention. The application may of course delete it at will. The UA should require permission from the user before granting persistent storage space to the application.
http://www.w3.org/TR/file-system-api/
> An application can request temporary or persistent storage space. Temporary storage may be easier to get, at the UA's discretion [looser quota restrictions, available without prompting the user], but the data stored there may be deleted at the UA's convenience, e.g. to deal with a shortage of disk space.
> Conversely, once persistent storage has been granted, data stored there by the application should not be deleted by the UA without user intervention. The application may of course delete it at will. The UA should require permission from the user before granting persistent storage space to the application.