code: @Override
      public Void visitClass(ClassTree node, Set<String> p) {
          scan(node.getModifiers(), p);
          scan(node.getTypeParameters(), p);
          scan(node.getExtendsClause(), p);
          scan(node.getImplementsClause(), p);
          scan(node.getMembers(), body);
          return null;
      }
docs: -- Differentiate declaration references from body references ---