Execution of a REWIND statement causes the specified disc file to be positioned
at its initial point.
<value> specifies the unit number. The keyword and equals sign are
optional if this is the first item in the list. If unit number is the only
argument, the brackets around the argument list are also optional.
<variable> will contain zero if the operation was successful, otherwise a
positive value to indicate an error.
<label> specifies a label to go to in the event of an error.