I got this from:
http://web.singnet.com.sg/~limttk/combat.htm (more evidence that Dian Xue exists)

The Four Advanced Yang Taijiquan Combat Skills
"There are situations where the skills and principles above require some augmentation to make them even more effective. This is usually where the opponent's skill level is high enough so that an effective counter is not possible using less injurous means. With such situations stronger discouragement is required and to cater for such eventualities, Yang Taijiquan has four advanced combat skills. These four skills can only be learned and applied effectively after one is able to understand each individual portion of any technique. In other words, one must be able to comprehend and put into practice the feet, tenths, hundreth parts and thousandth parts in Taijiquan. These four skills are recorded in the handwritten manual handed down from Yang Lu Chan. It must be noted that the four skills are not used entirely on their own but are integrated to form a comprehensive system of attack and defence built upon the basics of stability, sensitivity, agility and efficient use of the body and energy.

Bi Xue
"Sealing Accupoints"
This is also known as `Hitting Accupoints' and is more commonly known among Chinese martial artists as Dian Xue or `Dotting Accupoints' because the majority of these kinds of attack make use of the fingertips. Attacking accupoints is by no means unique to Taijiquan but the way it is done is certainly quite unique. Whilst other martial arts often make use of serious conditioning of the anatomical weapons and vigourous body conditioning to develop the strength and resistance required to hit accpoints, Taijiquan uses positional and structural advantage to let the opponent provide the power to hit himself with his own power and mass.

Accupoints are divided into fatal and non-fatal accopoints. Fatal accupoints are only used in a life and death situation as they are cause death very quickly and should not be used indiscriminately. Non-fatal accupoints are used to simply disable or incapcitate the opponent without causing too much harm. There are also accupoints that are more effective at different times of the day depending on the qi flow in the body. These timed strikes are of a more insidious nature as they are used for delayed killing or assassinations.

A short list of some of the accupoints used in Taijiquan is provided but readers are advised against using them unless absolutely necessary and to refrain from experimentation as the recovery techniques should be properly understood before one should practice with accupoints. Even then it is advisible not to practice them with any sort of impact since any accupoint strike on the body is a severe disruption of the body's systems and will have an affect on health of the body, both in the long term and in the short term. In most cases, even after remedial massage and accupoint treatment is carried out, herbs are taken to strengthen and stablise the body in order to eliminate any after effects."

Another quote I found from that site:

Cheng Man Qing On San Shou

"San Shou means free fighting. There is no definite method to it. Both T'ui shou [Push Hands] and Ta Lu issue from familiarity with the correct touch. From familiarity with the correct touch you will learn to t'ing jing [listen to strength]. After learning t'ing jing, you will gradually comprehend tung jing [understanding trength]. After comprehending tung jing, nothing any longer seems touched or not touched, scattered or not scattered, adhered to or not adhered to, followed or not followed. All are unnecessary explanations. They do not touch on the main point. The way of San Shou is located in the Five Elements and called chin, t'ui, ku, pan, ding. If you can tung jing and know the technique, then the application is complete. I followed Professor Yang for seven years and only one jing was difficult to learn. It was chieh jing [receiving jing]. If your achievement reaches this level then you do not have to worry about the other kinds of jing. The explanation of chieh jing found through the analogy of someone throwing a ball to hit me. If I resist the ball or hit it, it will bounce out. This is the jing of colliding and is not chieh jing. If the ball is light, it will be easy to bounce it out. However, if the ball's weight is several hundred pounds, how can I bounce it out? Hence, colliding is not correct. You must attract it and then toss it out. This is chieh jing. If the ball is moving slow or fast, or is light or heavy it is still he same. Chan [adhere], t'ing [listen], t'i [raise], fang [discharge] are all in it. Combine attraction and discharge almost simultaneously. The power is intensified in a very small space. This almost attains the highest wisdom in which San Shou becomes meaningless. Therefore, I say nothing can replace T'ai Chi Ch'uan. It is the supreme. Besides chieh jing there is nothing else."