Component rules are context-sensitive
Component rules apply to components, not types. It applies to data in a certain context when the data is a component of a given group.
Suppose you have some order data that contains two kinds of records: a regular order record and a bulk order record. In the bulk order record, the quantity ordered must be greater than 1000. In the regular order record, the quantity can be any number. You could put a rule on the quantity ordered component of a bulk order, but not on the quantity ordered of a regular order.