For people who don't understand why this is so significant.
Currently in SRB2, polyobjects (in laymans terms, level geometry which can move horizontally) currently have a visual bug in that the flats (the top and bottom of the objects) do not render properly. This means that the object looks invisible from above and below. For example, the horizontally moving platforms in ACZ in SRB2 2.0
As such, polyobjects in SRB2 are currently used solely in places where STJR can hide the top and bottom of them. Such as the walls pushing you into the slime in THZ2, or the crushing gears near the end of ERZ2.
This is a really good change, because having access to horizontally moving geometry without having to find ways to hide the missing flats open up many new possibilities for level designers. The simplest and most obvious example would be horizontal moving platforms.
The more you know~