TinyMCE

I had heard that tinyMCE was included in what was called a “trunk” version of WordPress. I’ve been interested in using TinyMCE, but I haven’t figured out what a “trunk” version is. I searched the site and found no references to either “trunk” or TinyMCE. If someone could shed some light on what a “trunk” version is, and where I could get it, I would be very appreciative.