[XeTeX] Portable code and xetex

[rhino64 at postmail.ch]

Hi All,
     I want to develop/adapt some personal styles to XeTeX (to include
polyglossia instead of babel for instance).

I want however to keep the compatibility with other TeX engines. Long
ago I have used a portable test but I don't remember exactly the command.

I have done a quick research on the web, but without much interesting result.
For what I remember, the command was similar to "\ifXeTeX...".

Any ideas would be greatly appreciated.

best regards,