"Zen is about being in the moment. The present is the only place you can be. That is why it is the best place to be.” That is what I was told recently being the-state-of-the-art of Zen meditation instruction in a city of America. It is not a kind of religion, but a state of mind, as the students were told. More philosophy than sound meditative practice I would say.
Some time ago, I read about Charles Luk's own meditative experience in the appendix of his book "The secret of Chinese meditation". He said he took up meditation to improve his health condition. After daily practice of seated meditation with an empty mind for a diligent period of over a year, he felt a current of warmth rising up along his spinal cord and he felt a state of happiness. It is interesting to note that Charles Luk, an active Zen practitioner, was a student of XuYun [虛云] (a lineage grandmaster of Zen tradition), and he seemed not knowing much about meditation techniques! It is also interesting to note that Charles Luk was the translator of the book "Taoist Yoga: Alchemy & Immortality" a famous Neidan text (of the WuLiu [伍柳] tradition). I can therefore safely conclude that the subtle art of meditation has been lost in contemporary Zen Buddhism.
If Charles Luk's translation of Taoist Yoga aimed at setting a good example for Zen practitioners to learn meditative techniques from the Taoist tradition, contemporary Zen practitioners should follow his footstep.
Based on my limited study of Zen classics, the practice of holding onto "Emptiness" or the "Present" during meditation is called "Stubborn Emptiness" (頑空). On practice level, during one's meditation, a triangular focus of hands and abdomen will generate chi. And chi thus generated will necessarily has a gradient of concentration, i.e. a feeling of concentration in particular areas of the body, usually areas with blockages. During such situation, the mind should relax its hold on emptiness, and subtly direct the chi to fill the area of emptiness, until the emptiness becomes filled. In other words, emptiness should be a dynamic process of seeking rather than a static process of being.
On a philosophical level, a Zen practitioner needs not look too far away than paying attention to the definitive verse of the Heart Sutra:
Body means Emptiness
Emptiness means Body
A Zen practitioner should not be afraid to pick up anything, he should have the confidence to pick it up now and put it down later!