I was participating in some discussions online and learned some information about the cross hands that are used in the hand forms as markers between the different sections.
If you study well you know that cross hands as found in Chens tyle is all throughout the form, it is found in many many places, such as in every grasp sparrows tail sequence. However the cross hands that is used to punctuate the form by dividing the sections is more interesting, evidently it is totally absent from pre-Chengfu forms and is one of the additions that Chengfu made.
It can be used to identify forms in terms of origination, all forms with this posture as punctuation draw from Yang Cheng-fu. Cross hands as a section marker is absent from material originating before him. This can also be used to identify cases of fraud or misunderstanding in that forms said to be before Chengfu that have this posture in it are not genuine.
It is a very interesting thing.
Here is a good example of some old style taiji, cross hands is not there:
http://youtu.be/ufhAXyrDG3E
another real one
http://youtu.be/BPvAFPD8x4E
here is an example of one said to be from Yang Jian Hou, but it is not, it is a modified Chengfu version:
http://youtu.be/ID-vsBdRjAk
Another one that is not what it is said to be:
http://youtu.be/2DNGJfP5dBY
There are also some moves totally absent from the modified Cheng-fu forms that are in all forms coming from Yang Luchan's students. If you study close you can see them quite easily.
I know this is very controversial because it outs a lot of claims of lineage. When I first learned of it I did not want to believe it, and I tried to study it in detail to disprove it, I ended up having to admit it was right on the money.