there are three master pages that call each other, and the files are in the www dir of your service dir (where you should find license and readme.txt, etc, packages, etc).
They are each separated into .adp and .tcl, and they are called blank-master, default-master and site-master. The .tcl files have varying amounts of info, with blank-master.tcl having the most extensive, and it is this file which describes doc(title) and other variables and procs, all useful to customize the page that calls <master>.
Take a look at (your service)/www/blank-master.tcl to read about everything these master templates can do.
