You can create many rules to form a full set of rules, and then apply multiple rules to categories and folders.
When you select the Manage Rules action for a category/folder with defined rules, the Rules page is split into two.
The left side of the page lists the rules that make up the rule set. If the category/folder inherits rules from a parent category/folder, those rules appear here too. The rules run in the order they're listed. Inherited rules are always run first.
A check mark to the left of the rule means it's active.
Selecting an individual rule in this list displays its details on the right side of the page.