[XeTeX] Testing for XeTeX

[Philip TAYLOR]

Michiel Kamermans wrote:

>> OK, thanks Ulrike/Wolfgang : I can therefore just
 >> modify my existing code to read :
>>
>> \ifcsname XeTeXrevision\endcsname
>> 	\font \tenrm = "Optima" \rm
>> \fi
>>
>> which does indeed work satisfactorily.
>
> You can, but now you're testing for XeTeX and then issuing plain TeX
> when you're indeed in it, which seems a little odd (the TeX code will
> compile fine regardless of which TeX flavour you use...). Why do you
> need the XeTeX test here?

Oh, for exactly the reason that Ulrike has already identified :
I want to fall back on CMR if I am using PdfTeX, but to take
advantage of my type-1 Optima if I am using XeTeX.

I realise that the chances of Don implementing it are
indistinguishable from zero, but it would be really nice
if the next release of TeX (real TeX) allowed one
to gain access to the banner line

	This is TeX, Version 3.1415926 (Web2C 2009)
	This is pdfTeX, Version 3.1415926-1.40.10 (Web2C 2009)
	This is XeTeX, Version 3.1415926-2.2-0.9995.2 (Web2C 2009)

from within a TeX program. If TeX were to provide access,
all derivatives could then do likewise, and we would have
a universal mechanism for determining in which environment
our code is running (modulo format, which is unfortunately
not known at this point, but that could be similarly addressed
if it is not already possible).

** Phil.