Try adding a rationale

p4-16/spec/P4-16-spec.mdk

@@ -2585,6 +2585,13 @@ The table below lists all types that may appear as base types in a
 | a `type` name     | allowed            | allowed         |
 |-------------------|--------------------|-----------------|
 
+Rationale: `void` is not useful except for specifying a function or
+method that does not return anything, therefore there is no reason in
+aliasing it and it could be confusing. `match_kind` values are not
+useful to store in a variable, as they are only used to specify how
+to match fields in table search keys, which are all declared at
+compile time and the declaration does not contain type.
+
 [^type_allowed]: `type B <name>` is allowed for a type name `B`
     defined via `typedef X B` if `type X <name>` is allowed.