make it clear that flat doesn't recurse and show how to do that

doc/Type/Any.pod6

@@ -195,6 +195,21 @@ in the process.
     say ((1, 2), (3)).elems;        # 2
     say ((1, 2), (3)).flat.elems;   # 3
 
+Please not that C<flat> is not recursing into sub lists. You have to recurse by
+hand or reconsider your data structures. A single level of nesting can often be
+handled with L<destructuring|/type/Signature#Destructuring_Parameters> in
+signatures. For deeper structures you may consider L<gather/take|/syntax/gather
+take> to create a lazy list.
+
+    my @a = [[1,2,3],[[4,5],6,7]];
+    sub deepflat(@a){
+        gather for @a { 
+            take ($_ ~~ Iterable ?? deepflat($_).Slip !! $_) 
+        } 
+    };
+    dd deepflat(@a);'
+    # OUTPUT«(1, 2, 3, 4, 5, 6, 7).Seq␤»
+
 =head2 method eager
 
 Interprets the invocant as a list, evaluates it eagerly, and returns that