docs: def select_parser(self, request, resource):
          """ Select appropriate parser based on the request.
  
          :param request: the HTTP request
          :param resource: the invoked resource
          """
  
          # 1. get from resource
          if resource.mapper:
              return resource.mapper
          # 2. get from content type
          mapper_name = self._get_name_from_content_type(request)
          if mapper_name:
              return self._get_mapper(mapper_name)
          # 3. get from url
          mapper_name = self._get_name_from_url(request)
          if mapper_name:
              return self._get_mapper(mapper_name)
          # 4. use resource's default
          if resource.default_mapper:
              return resource.default_mapper
          # 5. use manager's default
          return self._get_default_mapper()