The new task body model (or just body model) allows a task to have
multiple bodies. Generally a body is mapped to the execution of the same
user code of the task with specific input arguments.
The body model can constraint if a given body can be paused or re-run
again (resurrect).
Additionally, the body model can run multiple nested bodies but with the
restriction that the parent body should be paused first. This condition
can be relaxed with the BODY_FLAG_RELAX_NESTING flag.
