§A.7 Guard predicates

§ A.7.1 Guard
[base] when ( Expression )
§ A.7.2 MethodDeclaration
...
MethodHeader [Guard] MethodBody

Other rules referring to Guard: ClassDeclaration (§A.1.1), CallinBinding (§A.3.3)

Contextual constraints:
  1. The Expression in a guard must have type boolean.