+{- | Returns the pathname of a directory in which application-specific
+data for the current user can be stored. The result of
+'getAppUserDataDirectory' for a given application is specific to
+the current user.
+
+The argument should be the name of the application, which will be used
+to construct the pathname (so avoid using unusual characters that
+might result in an invalid pathname).
+
+Note: the directory may not actually exist, and may need to be created
+first. It is expected that the parent directory exists and is
+writable.
+
+On Unix, this function returns @$HOME\/.appName@. On Windows, a
+typical path might be
+
+> C:/Documents And Settings/user/Application Data/appName
+
+The operation may fail with:
+
+* 'UnsupportedOperation'
+The operating system has no notion of application-specific data directory.
+
+* 'isDoesNotExistError'
+The home directory for the current user does not exist, or
+cannot be found.
+-}