Add concept of stubbing a class should you need to

doc/Language/5to6-nutshell.pod6

@@ -1155,9 +1155,22 @@ C<is> keyword, in the class declaration.
 package Cat;
 use base qw(Animal);
 
-=for code :preamble<class Animal {};>
+=for code :preamble<class Animal {}>
 # Perl 6
-class Cat is Animal {};
+class Cat is Animal {}
+
+Note that the C<Animal> class must be B<known> at compilation time.  If for
+some you need to specify / load your modules in a particular order, you can
+create a stub that will be acceptable until the end of compilation: if the
+stub has not been defined then, compilation will fail.
+
+=for code :preamble<class Animal {}>
+# Perl 6
+class Animal { ... }       # the ... indicates a stub
+class Cat is Animal {}
+class Animal {
+    # the real thing
+}
 
 =head3 C<bigint> C<bignum> C<bigrat>