[support] Wireframes around regions in D7

[Hakan]

I was trying to find out how to add wireframes around a couple of
regions I had added to a new subtheme of the Zen theme in D7 after I
had successfully turned on wireframes for the standard regions. I began
by trying to find out how wireframes were turned on for the sidebars by
searching many files for region-sidebar-first (which can be found in
the wireframes.css file but could not find any reference to that class
in the source files I searched in both the subtheme and the Zen base
theme.

On a lark I simply converted the statement in my info file
"regions[triptych_1]	= Triptych 1" to region-triptych-1 which I
added to wireframes.css. Lo and behold, it worked! How, I have no idea,
nor did I find any reference by Googling.

Could someone explain how this is accomplished?

Thanks.