definetypeface usage

["dr. Hans van der Meer" <hansm@science.uva.nl>]

Trying to findout how ConTeXt's font mechanism works, I come to 
following question:

 From the brochure "Fonts in Context" (mfonts.pdf) I have picked up the 
notion that exercising a call to \definetypeface gets fonts in working 
order (see the examples there on font specifiers "funny" and "whow", 
for example, and the resulting typeface collection).
Also in file type-exa.tex there is a typescript [postscript] where 
\definetypeface is exercised, seemingly to bring a matched series of 
times, helvetica and courier into existence.
However, the usage of the postscript fonts via \setupbodyfont[pos] 
seems to be completely unconnected with this script (I traced the 
typescript checking). Neither can I find somany calls to 
\definetypeface (and its derivatives \dodefinetypeface and 
\dododefinetypeface); it seems they are barely used in the code.
So, the questions are:
- Does \setupbodyfont[pos] results in the scaled font set as given in 
type-exa?
- Or does \definetypeface belong to an alternative/obsolete font 
definition scheme, totally unrelated to the definitions called up in 
the scripts in type-pre.tex, type-syn.tex, and other friends?
- In preparing font scripts, can I therefore totally ignore 
\definetypeface or will that be disastrous for the result?

If somebody would be so kind to enlighten me...
Hans van der Meer