Why can not rm or rmtf fonts be set up by \definebodyfont macro?

[Yanrui Li <liyanrui.m2@gmail.com>]

These days I have been reading "co-fonts.pdf" because I plan to write
a document about
ConTeXt MkIV for our Chinese users. When I reached the part of
"Defining body fonts",
for testing bodyfont model, I made an example as following:

%%%%
\definefontsynonym[Song][AdobeSongStd-Light]
\definefontsynonym[Hei][AdobeHeitiStd-Regular]
\definefontsynonym[FangSong][AdobeFangsongStd-Regular]
\definefontsynonym[Kai][AdobeKaitiStd-Regular]

\definebodyfont[12pt][rm]
               [tf=Song,
                 bf=Hei sa 1,
                 it=Kai sa 1,
                 sl=FangSong sa 1]

\setscript[hanzi]
\setupbodyfont[rm,12pt]

\starttext

今时之人不然也，以酒为浆，以妄为常，
{\bf 醉以入房，以欲竭其精，以耗散其真}，
{\it 不知持满，不时御神}，
{\sl 务快其心，逆于生乐，起居无节，故半百而衰也}。

\stoptext
%%%%

I found that "rmtf" font is not "AdobeSongStd-Light", which is always
"LMRoman12-Regular".
However, "bf", "it" and "sl" fonts all are right.

I looked over the log file and saw some messages as following:

    fonts          : preloading latin modern fonts
    bodyfont       : 12pt rm is loaded

I want to know why I can not override the preloading rm font.

Thanks.

-- 
Best wishes,
Li Yanrui

* Gentoo Linux (~x86)
* ConTeXt Minimals Beta (2009.03.30 18:28)
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