[tex-hyphen] hyphenation different in xelatex?

[Philip Taylor]

Philip Taylor wrote:

> Reinhard Kotucha wrote:
> 
>> And pdftex is 100% backwards compatible with DEK's TeX.
> 
> Well, not really : compare the result of expanding (e.g.,)
> 
> 	\expandafter \ifx \csname pdfximage\endcsname \relax UNDEFINED\else
> DEFINED\fi
> 
> in the two engines ...

and of course, for exactly analogous reasons (\expandafter \ifx \csname
holdinginserts\endcsname \relax UNDEFINED\else DEFINED\fi), TeX 3 cannot
be 100% backwards-compatible with TeX 82.  But there may be other
reasons as well, which it is too late for me to think of this evening.

** P.