Documented text conflicts with class attributes. Training level is a part of task_group not plan_item.
18.104.22.168 Sub-plans and Re-use
The PLAN_ITME.training_level attribute can be used to set the experience level of sub-plans if required; implementing this behaviour at execution time would rely in the Plan execution engine using these settings.
6.7. Training Level
To enable a single Plan to be used in both ways, the concept of 'training level' is included in the model, on the TASK_GROUP class.
Class description also includes training_level as a part of TASK_GROUP (not inherited from from PLAN_ITEM)