[traps] comment why BUILDALL is a method, not a submethod

Author: moritz

lib/Language/traps.pod

@@ -98,7 +98,10 @@ C<BUILDALL> mechanism instead:
 
     say A.new(x => 42).x;       # 42
 
-
+(Note that C<BUILDALL> is a method, not a submethod. That's because by
+default, there is only one such method per class hierarchy, whereas C<BUILD>
+is expclitly called per class. Which also explains why you need the C<nexsame>
+inside C<BUIDLALL>, but not inside C<BUILD>).
 
 =head1 Regexes