Based on John Hicks article, here is how to add TextBook reference manual within Coda editor:

1. First, Command-6 to go to the books view, and click the add icon bottom left. In the sheet that appears, enter the title TextBook and the URL:
   https://docs.textpattern.com/tags/Category:Tag_Reference
2. Next, in the ‘use for mode’, select the language it references. In this case, choose PHP/HTML.
3. Finally, add the search URL. For TextBook website, this is this one: https://docs.textpattern.com/search/?q=*

If you wish, you can also drag in this image to represent TextBook.

Done! You can now access to TextBook reference manual directly within your Coda editor. Pretty useful.