No, it's any code and even things that aren't code. It will write and revise documentation for you, create jquery, nosql databases, and more. Basically anything a human can do with text files.

If that's not enough for you, projects like Auto-GPT give GPT-4 full autonomy to figure out how to do complex multi-step tasks beyond modifying text all on its own with only a vague goal provided. https://github.com/Torantulino/Auto-GPT

You can use this on any code (or text files) that you want. I've used this for rails, and it's great. I think you'd run into issues with more niche languages where the model hasn't had much exposure.