[XeTeX] Looking for a better font selection method

[Pektiong Tân]

Hi there,

   I have some similar questions.

   Some background information: In Taiwan, the language Taiwanese  
(http://en.wikipedia.org/wiki/Taiwanese_language ) is sometimes  
written in a mix-script which
   use traditional chinese characters and Latin characters. For the  
Latin characters part, an orthography called Pe̍h-oē-jī(POJ, http:// 
en.wikipedia.org/wiki/Pe̍h-oē-jī ) is used.
   POJ used many accented Latin characters, some of them don't have  
pre-composed unicode code point, and combining character must be  
used. Only font like Doulos SIL has
   proper support for POJ (has enough characters and enough opentype  
support). CJK font usually has only basic Latin characters (and of  
course no OT) and is not enough for POJ.
   Note that we are talking about a mix-script and the Latin  
character part is essential.

   When using XeTex to write in Taiwanese in mixed script I try to  
define font for CJK part and Latin part
   \font\hant="Apple LiSung Light" at 12pt
   \font\poj="Doulos SIL" at 12pt

   I can then set the CJK to be default and change to POJ when  
necessary, like

   \hant
   這是一本書{\poj Khó͘ Huī-koan tī kiat-lūn siōng bé-á  
ū án-ne siá}

   If I want to use bibtex, in my .bib file, I have to do something like

@ARTICLE{poj,
   author = {{\poj Tân, Pektiong}},
   title = {Góa ê Pe̍h-oē-jī Chiàⁿ-jī-hoat},
   journal = {{\hant 我的期刊}},
   year = {2007},
}

  If I don't add in those \poj, \hant in my .bib file, I didn't  
figure out a way to generate the reference correctly in my main latex  
file.

  Is there any better solution to the situation I have?
  I have read some posts which talk about the font fall back. I am  
not sure why font fall back is difficult but I am wondering,
  Can we assign DIFFERENT DEFAULT FONT TO DIFFERENT UNICODE BLOCK? In  
my case, if I can assing a CJK font to all CJK blocks and Doulos SIL  
font
  to all Latin blocks, then I would be very happy. Of course, I might  
need to adjust the font size for different fonts so that they match  
well.

best
pektiong