The default value for the preference, which will be set either if persistence is off or persistence is on and the preference is not found in the persistent storage.

May be a reference to another resource, in the form "@[+][package:]type:name" or to a theme attribute in the form "?[package:][type:]name".

May be a string value, using '\\;' to escape characters such as '\\n' or '\\uxxxx' for a unicode character.

May be an integer value, such as "100".

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

May be a floating point value, such as "1.2".

[Android Documentation]