$page = A:B:C->new();
  $page->check_if_i_should_be_a_subclass_instead();
  $page->render(); # render method from A:B:C or A:B:C:D1  based on ab
+ove method result
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This makes me think that what you might want is to separate out the rendering stuff into separate classes and then create your A::B::C object, passing in an appropriate rendering object.

my $renderer = Renderer::D->new;
my $page = A::B::C->new( renderer => $renderer );
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