Being based on the mentalist principles of the hidden teaching, they were traditionally regarded as being beyond yoga. Hence these exercises have been handed down by word of mouth only for thousands of years and, in their totality, have not, so far as our knowledge extends, been published before, whether in any ancient Oriental language like Sanskrit or in any modern language like English. They are not yoga exercises in the technical sense of that term and they cannot be practised by anyone who has never before practised yoga.
-- Notebooks Category 23: Advanced Contemplation > Chapter 6: Advanced Meditation > # 9
-- Perspectives > Chapter 23: Advanced Contemplation > # 39