Keiko has posted a detailed explanation of the high knockdown trick in Street Fighter Alpha 2, based on an old AGSF2 article by Omar DeLoney. It’s actually a very interesting and useful setup, which comes in handy for all kinds of juggle combos. Here’s the link and a brief quote:
High Knockdown Trick (HKD) on SFZ2 Blog
This is a very interesting and detailed old article that was posted over the first american SF Community (Before SRK ever existed), i’m talking about alt.games.sf2, this article was made back in 1998 but it still being the most informative and complete one about the High Knockdown Trick on SFA2.