BUILTIN is an entry name attribute that indicates that the declared name is a built-in function. Unless an empty argument list is used in a reference to a built-in function having no parameters, the function must be declared with the BUILTIN attribute.
BUILTIN can be used to redeclare a built-in function name that was declared as something else in an outer block. The declared name must be one of the names given in the chapter Open PL/I Built–Ins.