We're planning to add additional reference books as development of Coda continues.
Odds are, if it's a widely known web programming language, it's on our radar.
We're specifically looking for sources that are authoritative, can be licensed, and that we can re-format into our standard books format. We hadn't found books that met our standards for every language for our initial release.
If there's documentation available on the web for your language of choice, one workaround is to use a preview tab that points to it.
If you have further specific concerns about our reference books, please contact our support department!