code: public static boolean serialInclude(Doc doc) {
          if (doc == null) {
              return false;
          }
          return doc.isClass() ?
              serialClassInclude((ClassDoc)doc) :
              serialDocInclude(doc);
      }
docs: Return true if the given Doc should be included
  in the serialized form.
  
  @param doc the Doc object to check for serializability.