[plt-scheme] Overview of the various pieces of PLT?

Hi,

My understanding so far is that "PLT Scheme" includes the Scheme
interpreter (MzScheme), an IDE, and a large number of docs and
libraries, however the front page of the web site says PLT Scheme is a
language. Does maybe "PLT" refer to the whole system, and "PLT Scheme"
refer to the language itself?

Also, a few more questions:

* Is everything listed at <http://docs.plt-scheme.org/> included with
PLT? If not, is there a list somewhere showing what's included?

* Is "DrScheme" just the IDE, or does it include other pieces of PLT
as well? (What main pieces does it rely upon?)

* Is the PLT IDE itself written in Scheme?

* Is MrED the GUI toolkit for PLT? Is it written from scratch, or is
it implemented in a C GUI toolkit like GTK+ or Qt?

* If I install *just* MzScheme, what pieces of PLT will I not have?

Thanks!