Do roles get bound in the effect predicates of actions?

https://github.com/ensemble-engine/ensemble/wiki/Ensemble-API
has the following line "For example, you could have defined an "onlooker" role by setting it to the first or second property of a condition, influence rule, or effect predicate of an action."

Wouldn't the theoretical "onlooker" have to be in a condition or influence rule to get bound to a character?