“Raja Yoga, having been articulated by Patanjali, was then expanded upon by later teachers. Out of these teachings came the “Hatha Yoga Pradipika.” This is also known as the Yoga of Light or Kundalini Yoga. These teachings were shared by the original 14 great sages of India known as the Siddhars. Those who have achieved mastery of these techniques and, in doing so, have caused their prana to successfully move through the sushumna nadi (the heightened prana of kundalini) and to remain there are known as siddha yogis. This text further expounds upon:

•  The specific practices of asana and pranayama 
• The use of kriyas (yogic purification techniques) 
• The use of bandhas (muscular lock [tension] techniques for directing prana) 
• The use of mudras (body and hand positions used to seal (stabilize) the flow of prana
  
• While siddhis (yogic mystical powers) are attained via the successful practice of hatha yoga as outlined in the “Hatha Yoga Pradipika,” these siddhis are not meant to be an end in and of themselves and may in fact become a distraction, if one becomes attached to them. There are eight traditional siddhis though, surely, the siddha yogis are not limited to them. They are:
  

•  Anima: The power to assume a minutely small form 
•  Mahiman: The power to assume a very large form 
•  Garmiman: The power to become very heavy 
•  Langhiman: The power to become very light 
•  Prapti: The power to travel to distant objects 
•  Prakamya: The power to attain what is desired 
•  Isita: The power to shape or manifest anything that is desired 
•  Vasitva: The power to control 
• 
  The use of siddhis for the purpose of indulgence in any form is highly discouraged. They ideally come to the yogi only at the time they are no longer desirous of them for personal gain. The practices of hatha yoga are specifically for the purpose of accelerating one’s progress on the path of raja yoga for the attainment of kaivalya (absolute freedom) and the de-evolution of individual consciousness.”
• ~ Excerpt from “Principles of Ayurvedic Medicine,” by Dr. Marc Halpern, Founder of the California College of Ayurveda