>> in LaTeX, there are *really* differences depending on the engine.
>
> Oh, really? Color me surprised. Are there tools other than build
> systems that read those environment variables? And users set them
> globally, in spite of the incompatibilities that exist between the
> TeX engines?
There are a bunch of LaTeX packages that only work with a specific TeX
engine, and which need special input code for that. For example,
`fontspec` (with its excellent OpenType support) only works with XeTeX
and luatex. Or think of 'lyluatex', which obviously needs luatex.
On the other hand, `texinfo.tex` aims to work identically with all
engines for a given input, producing identical output – until now: the
'microtype' feature is, AFAIK, the first typographical improvement not
available in all TeX engines.
Werner
