On a scale of LaTeX=0 (absolutely inscrutable) to Rust=10 (holds your hand through the fix) I would say SILE is about a 5. Caveat, I speak as one of the authors. It helpfully traces the location of any problem to an exact location in your document, mostly clarifying what it was trying to do, has a trace stack with code locations for everything it was trying to do leading up to the problem, and in many common cases has sensible descriptive errors. That being said if even as a contributing author I only give it a 5 it clearly has room to improve!