Option to let applications specify that user data can/cannot be cleared. This flag is turned on by default. This attribute is usable only by applications included in the system image. Third-party apps cannot use it.

Must be a boolean value, either "true" or "false".

This may also be a reference to a resource (in the form "@[package:]type:name") or theme attribute (in the form "?[package:][type:]name") containing a value of this type.

[Android Documentation]