Adding a `definitions` part

You add a definitions part in a rule to create variables that can be used within the rule, and to simplify certain expressions.

Rule variables
A rule variable has a name to which you assign a value and is used to refer to a population of objects rather than a particular object. You define the variable in the definitions part of a rule, and you can use it only in the condition and action parts of the rule that declares the variable.
Types of rule variables
A rule variable can represent a constant, an expression, an object, or a collection of objects.

Parent topic: Writing rules