["... code that's going to be used to make a Vista theme."]
https://www.tcl-lang.org/man/tcl8.6/TkCmd/ttk_vsapi.htm
MG The manpage for ttk_vsapi tells you to refer to the Microsoft docs for valid values for classname and partid. They are always somewhat of a nightmare to navigate (and, sadly, regularly move around), but currently you can find the info http://msdn.microsoft.com/en-us/library/windows/desktop/bb773210%28v=vs.85%29.aspx%|%here%|% on MSDN. That page tells you to check Vsstyle.h which I found online easily with the almightly Google.