Brr_io.StorageSourceStorage objects.
See Web Storage API
local w is the storage saved accross page sessions for the window's origin.
session w is the storage cleared when the page session ends for the window's origin.
length s is the number of items in s.
key s i is the name of the ith key. (N.B. local storage can race with other tabs)
set_item s k v sets the value of k to v in s. An error is returned if the value could not be set (no permission or quota exceeded).
remove_item s k removes the value of k from s. If k has no value this does nothing.