code: def _validate_doc_refs(self):
          
          for namespace in self.api.namespaces.values():
              env = self._get_or_create_env(namespace.name)
              # Validate the doc refs of each api entity that has a doc
              for data_type in namespace.data_types:
                  if data_type.doc:
                      self._validate_doc_refs_helper(
                          env,
                          data_type.doc,
                          (data_type._ast_node.lineno + 1, data_type._ast_node.path),
                          data_type)
                  for field in data_type.fields:
                      if field.doc:
                          self._validate_doc_refs_helper(
                              env,
                              field.doc,
                              (field._ast_node.lineno + 1, field._ast_node.path),
                              data_type)
              for route in namespace.routes:
                  if route.doc:
                      self._validate_doc_refs_helper(
                          env,
                          route.doc,
                          (route._ast_node.lineno + 1, route._ast_node.path))
docs: Validates that all the documentation references across every docstring
          in every spec are formatted properly, have valid values, and make
          references to valid symbols.