Sf4 Series hitstop and blockstop

Does anyone know how the hitstop/blockstop system in the sf4 series works or where the information is located on the internet? Neither google nor the srk search function has pulled anything up and I don’t have it bookmarked nor, now that I think about it, have I seen it since I started playing this game. Thanks in advance.

This has some info (read comments as well):

And look in the comments here:

thanks, giving these a look thru right now