There are four permissions levels and they are
as follows:normal (not a dangerous one and considered as
an application-level permission); dangerous (a more risky
permission could access, without the asking the user to
confirm; a sensitive data or damaging functions);
signature (a permission can be granted only to other
packages that are signed with the same signature);
andsignature-or-system (a special type of signature permission
that's existing to manipulate with the legacy
permissions).