def _task_validations(self, config: "PoeConfig", task_specs: "TaskSpecFactory"):
            """
            Perform validations on this TaskSpec that apply to a specific task type
            """

            import shlex

            task_name_ref = shlex.split(self.content)[0]

            if task_name_ref not in task_specs:
                raise ConfigValidationError(
                    f"Includes reference to unknown task {task_name_ref!r}"
                )

            if task_specs.get(task_name_ref).options.get("use_exec", False):
                raise ConfigValidationError(
                    f"Illegal reference to task with "
                    f"'use_exec' set to true: {task_name_ref!r}"
                )

            Perform validations on this TaskSpec that apply to a specific task type
            
poethepoet/task/ref.py