If there ever was a post graduate study and application of yoga, then Patanjali’s Sutras are it. They map the path, show the way and reveal the elevated stages which are hard to reach even for those who mastered astral projection and third eye perception.
Chapter 1 gives the description and layout of samadhi transcendence accomplishment. Chapter 2 explains practice accomplishment. Chapter 3 shows the glory which may be attained by a persistent yogi. Chapter 4, the last, tells the yogi how to make the segregation accomplishment where the core-self is disconnected from its perception equipments and realizes itself as itself.
In the last chapter, there is an explanation of how to safely unify again with the perception equipments after the core-self is isolated from these. At the time of publication, there is no other media that goes into so much detail about advanced yoga practice.