Answering both: dial image for reference to what the “modes” are, and my dial is gross. Plus that was the best image I could find describing it, but had trouble getting a clean download. Google images can suck that way. If you get me a clean link, I’d update the post.
Sadly front end, like “High Level” is a very relative term. For example, in compiler design, the bit that parses code is called the “front end” since the “back end” is what emits machine code. I think that’s what they mean here, the “front end” that understands D3D8 code has been added, presumably there is also a “back end” that converts the parsed/analyzed D3D8 code into valid opcodes for consumption by GPU/CPUs.
In the other direction, a UI/UX is sometimes called a “back end” when it is part of a more complex embedded project where physical controls are the “front end”.