We have this already. You can ask Cursor to go read the doc on syntax it may not have ever seen and write something that conforms. I used this recently to support a new feature in Lit which I'd never seen before and I doubt is in the training set much, if at all.

You can also describe your own app's syntax, architecture, function signatures, etc. in markdown files or just in chat and Cursor will write code that conforms to your desired syntax, which definitely doesn't exist in the training set.