Thanks for the descriptions. I have made a small test and turns out the "regularfont" has to be assigned to something or the other "xxxfont"s won't have any effects.

Here's my code:
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\definefallbackfamily [mainface] [serif] [adobesongstd]
  [range={0x00400-0x2FA1F}%
  ,regularfont=name:adobesongstdlight%
  ,italicfont=name:adobefangsongstdregular%
  ,boldfont=name:adobeheitistdregular%
  ,bolditalicfont=name:adobekaitistdregular%
  ,force=yes%
  ,features=song%
  ]
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and if I remove the "regularfont=..." line, the boldface Chinese characters will use the Adobe Song Std font as well. Same thing happened when I used the "preset=xxx" option which I don't know if it is intended to behave like that, by the way.     

Oh, and off the topic, can I use "effect" to assign the fonts? Like if I have defined
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\defineeffect[mybold][alternative=both,rulethickness=\dimexpr\bodyfontsize/10\relax]
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I would like to use this effect to apply to my bold fonts, maybe:
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\setupfontfamily [serif] [DejaVu Serif] [boldfont=effect:mybold]
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I know this has nothing to do with this module. I just thought this might be interesting.