On the syntax verification aspect, so far, so good.
Using the previous example as a jumping point, I've implemented basic syntax awareness within the generated parsers. Left-recursive rules seem to be a bit 'iffy' but I'll be rewriting that area of focus soon anyway (I think I hit upon a pattern in the approach, it's just an arduous process.)
Below is a screenshot of a grammar file 'Errors.oilexer' which has an error at character 4, a '-'.
Oilexer (bottom) seems to somewhat disagree on what's valid at this point: