Adds clarification to void type

Follow @zoffixznet comment in rakudo/rakudo#1982.

Author: JJ

doc/Language/nativecall.pod6

@@ -616,14 +616,14 @@ leaks.
 
 =comment TODO
 
-TBD
+L<Blob>s and L<Buf>s are Perl 6 way of storing binary data. We can use them for interchange of data with native functions and data structures, although not directly. We will have to use L<C<nativecast>|/routine/nativecast>.
 
 =head1 Function arguments
 
-NativeCall also supports native functions that take functions as arguments.  One example
-of this is using function pointers as callbacks in an event-driven system.  When
-binding these functions via NativeCall, one need only provide the equivalent signature
-as a constraint on the code parameter:
+NativeCall also supports native functions that take functions as arguments.  One
+example of this is using function pointers as callbacks in an event-driven
+system.  When binding these functions via NativeCall, one need only provide the
+equivalent signature as a constraint on the code parameter:
 
     use NativeCall;
     # void SetCallback(int (*callback)(const char *))

doc/Language/nativetypes.pod6

@@ -99,9 +99,10 @@ valid type, you can use it in expressions:
      my void $nothing;
      say $nothing.perl; # OUTPUT: «NativeCall::Types::void␤»
 
-In practice, it is an C<Uninstantiable> type that can rarely be used by itself.
-However, it is generally found in typed pointers representing the equivalent to
-the C<void *> pointer in C.
+In practice, it is an C<Uninstantiable> type that can rarely be used by itself,
+and in fact it is L<explicitly forbidden in C<return> types|/language/nativecall#Passing_and_Returning_Values>. However, it is
+generally found in typed pointers representing the equivalent to the C<void *>
+pointer in C.
 
 =begin code :preamble<use NativeCall;>
 sub malloc( int32 $size --> Pointer[void] ) is native { * };