Clarify class literals for primitive types (#5)

proposals/bound-callable-references.md

@@ -220,7 +220,8 @@ class A {
 }
 ```
 
-Generated bytecode for `<expr>::class` should be similar to `<expr>.javaClass.kotlin`.
+Generated bytecode for `<expr>::class` should be similar to `<expr>.javaClass.kotlin`. Note that for expressions of primitive types, the corresponding `KClass` instance at runtime should be backed by the primitive `Class` object, not the wrapper class. For example, `42::class.java` should return the `int` class, not `java.lang.Integer`.
+
 An intrinsic for `<expr>::class.java`, meaning `<expr>.javaClass`, would be useful.
 
 ### Reflection