The definition of control constructs, directives and built-in predicates is presented as follows:
Specifies the types of the arguments and which of them shall be instantiated (mode). Types and modes are described later (section 6.2).
Describes the behavior (in the absence of any error conditions). It is explicitly mentioned when a built-in predicate is re-executable on backtracking. Predefined operators involved in the definition are also mentioned.
Details the error conditions. Possible errors are detailed later (section 6.3). For directives, this part is omitted.
Specifies whether the definition conforms to the ISO standard or is a GNU Prolog extension.