[XeTeX] A general suggetion for managing the font selection for mixed-language document

[Song Zhiwei]

Many users is going to manage the font selection for mixed-language
document. This can be done by adding a feature of "Unicode" for
\fontsec like the feature of "Size".

An example:

\fontsec[UnicodeFeatures={
  {Unicode=-00FF,Font=Times New Roman,OutterSpace=0pt plus 0.3pt}
}]{Adobe Song Std}

Here, the OtterSpace is the additional skip length when  entering or
quiting the range of Unicode (unicode < 00FF in this example), Font is
the alternative font if  Unicode < 00FF.

You can see that it is a general method for any languages.