Annotation is a form of metadata that is added to a function of a dApp script.
At the present moment, there are two annotations:
@Verifier(tx). The variable name in the annotation is required even if the function does not use it.
An annotated function cannot be called inside a dApp script.
Annotation of a callable function.
i contains an Invocation structure representing certian fields of the invocation.
Annotation of a verifier function.
tx contains a structure of transaction or order sent from a dApp's account.