[XeTeX] Mapping inside font definition

[Mehdi Omidali]

Hi everyone,
Is it possible to declare a font mapping inside a font definition like
\newfontinstance\myfont[Script=Arabic,Mapping="U+0030 <> U+06F0"]{Scheherazade}
If it is not possible, is it possible to define a font mapping file and put it
in the running directory so that fontspec can find it?
And as a general comment to the Mapping procedure: it seems that if one puts an
specific font mapping (like Mapping=farsidigits) in a font definition and the
mapping file is not included in the tex distribution, then fontspec will not
complain about that ( such that "undefined farsidigits mapping"). Am I right?
Thanks