The item list consists of one or more item descriptors, each of which is three longwords. The descriptors can be in any order in the item list. Each item descriptor specifies an item code. Item codes are specified as either input or output parameters. Input parameters modify functions, set context, or describe the information to be returned.
Output parameters return the requested information.
The item list is terminated by a longword of 0. The astadr argument is the address of the AST routine. The astprm argument is a longword value containing the AST parameter.