Will Robertson <[log in to unmask]> writes:

>> ? If so, is there a simple implementation of \ifThisIsXeTeX ?
>
> Pretty much, yes.
>
> The ifxetex package provides \ifxetex (simply by checking for the
> presence of \XeTeXversion).
>
> Here's some code that does approximately the right thing: (intended to
> be a self-contained package in a XeTeX-exclusive search path to
> override the normal inputenc.sty)
>
> %%%%%%%%%%%%%%%%%%%%%%%%%%%%
> \ProvidesPackage{inputenc}
>   [2008/05/15 v0.1 XeTeX-specific inputenc package]
> \typeout{%
>   Loading a XeTeX-specific package to
>   override LaTeX's inputenc package.}
> \RequirePackage{ifxetex}
> \RequireXeTeX

We would not want to have an external package dependency like that if we
wanted to make this part of the LaTeX base package.  So we would likely
check for \XeTeXversion ourselves here.

Also we would not want to go over Jonathan's head here: are you in
contact with him?  We certainly would want to provide a solution that
does not mess up his plans and the typical use cases of XeTeX users.

-- 
David Kastrup