It's not really even "by default" -- that suggests you could change it from the default. It's generally really hard to stick any custom error messages of any ki

It's not really even "by default" -- that suggests you could change it from the default. It's generally really hard to stick any custom error messages of any kind into a generated parser. You're often limited to making your grammar accept things that are wrong, and then writing a check that detects those invalid situations in the resulting AST. The parser generator doesn't understand any specifics about your language, so it's not capable of producing useful errors by itself in essentially any situation at all. If you're lucky, you can get "I didn't understand this token at this position; here's a list of other tokens that would have been valid." Meanwhile, with a hand-rolled recursive descent parser, you are writing literally every error message yourself. You can generate an error from anywhere you'd like, using any information you need (local or global!), since it's all just code that you're writing. I have a large-ish grammar that I spent a lot of time on, and I'll be damned if I don't still sometimes get "Invalid statement." with no useful location information. I even wrote my own parser generator; it's not just a shortcoming of existing tools, it's just really hard to write a generic parser generator that's capable of generating custom and useful errors.