some more X::Comp notes

lib/X/Comp.pod

@@ -12,6 +12,12 @@ returned from the L<backtrace> method is not very informative. Instead
 the exception carries its own C<filename>, C<line> and C<column> attributes
 and public accessors.
 
+If an error occurs while creating an object (like a class or routine) at
+compile time, generally the exception associated with it does not hold a
+reference to the object (for example a class would not be fully composed, and
+thus not usuable). In those cases the name of the would-be-created object
+is included in the error message instead.
+
 =head1 Methods
 
 =head2 filename