I am away from my Mac for the moment and I wanted to look up some documentation online. So I went to inform7.com and looked in Write -> Extensions. But there are no documentation/source links for the built-in extensions. So I went to Manuals. But there are no documentation links for any extensions there! Is information about the built-in extensions even available on the site?
No. I suggest adding a comment/suggestion on the UserVoice forum if you’d like to see this done, as the extension volunteers are currently going over the system.