Combining.
(or{{typespec}*})
| typespec | a type specifier. |
This denotes the set of all objects of the
type determined by the union of the typespecs.
For example, the type list by definition is the same as (or null cons).
Also, the value returned by position is an object of type (or null (integer 0 *));
i.e., either nil or a non-negative integer.
* is not permitted as an argument.
The type specifiers (or) and nil are equivalent.
The symbol or is not valid as a type specifier;
and, specifically, it is not an abbreviation for (or).