code: def validate(self, messages):
          
          messages = self.validate_version(messages)
          messages = self.validate_data_lics(messages)
          messages = self.validate_name(messages)
          messages = self.validate_spdx_id(messages)
          messages = self.validate_namespace(messages)
          messages = self.validate_ext_document_references(messages)
          messages = self.validate_creation_info(messages)
          messages = self.validate_package(messages)
          messages = self.validate_extracted_licenses(messages)
          messages = self.validate_reviews(messages)
  
          return messages
docs: Validate all fields of the document and update the
          messages list with user friendly error messages for display.