[T] essence of being is originally pure and, in relation to its self-manifestation, [is free from] transitory defilements of delusion, which have been purified directly upon the basis of being. This essence of being is designated by the term “Unsurpassed Realm”. It is the basic space of phenomena, the self manifest sacred circle of essential awakening not belonging to minds [of beings in] the ten directions, and not defined by size, limits, or orientation.
The Treasury of Knowledge: Books Two, Three, and Four
Buddhism’s Journey To Tibet
by Jamgon Kongtrul Lodro Taye
translated by Ngawang Zangpo : page 541