Commented Unassigned: "Update Level Rules" vs. "Package Level Rules"? [301]

Have to make custom updates and have problems with the rules.

Is there any documentation about the difference between "Update Level Rules" and "Package Level Rules"? Which type of rules shoud be used for custom updates?

Thank you all in advance for any hint.
Franz
Comments: Thank you for your explications! So, when I understand this correct: In WPP, does in makes no difference in practice if Update- or Package Level Rules are used? Kind regards, Franz