[texhax] font fallback

[bill lam]

In latex cjk package it includes arphic font "bsmi" but it missed some
glyphs so that I installed another font "song".  However some
computers may not have this new font installed and latex aborted.  How
to specify to use the font "song" as default but fallback to "bsmi" if
"song" is not available.  Can this be done by two different methods

1/ configure texlive itself
2/ conditional branch inside source of latex file

relevant portion of my font specification for cjk,

\newenvironment{TChinese}{%                                                                                  
\CJKfamily{bsmi}%                                                                                            
\CJKtilde                                                                                                    
\CJKnospace}{}

-- 
regards,
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