The only Sub Rules decision is the Sub Rule decision node.
Use sub rules to add complexity to your rule, without taking up additional space in the rules canvas. Sub rules group a complex series of decisions that make up a single action or outcome; for example, to group rule branches used for segments or A/B tests of users.
Enter a title for your sub rule in the Title text box.
When you save a sub rule, it opens in a new rules canvas. You create a sub rule in the same way as a rule.
For further information on using sub rules, see the Simplify User Journeys with Sub Rules section. This section steps you through the creation of a rule that uses nested sub rules to simplify journeys by traffic type.