[tgv]

IMO, a more complex grammar allows for better descriptions. The only real type of grammar simpler than CFG is a regular expression. That's pretty limited, although (the older part of) CSS doesn't need more than that. But as soon as you want a nested construction, hierarchy or simply nested parentheses, you need a CFG. If it's difficult to configure, the problem is the (configuration) language, not the power of its grammar.

And there are excellent parser generators out there. You don't have to fear introducing bugs via them.