On 04/08/2011 18:10, Ulrike Fischer wrote: > You mean \pdftex_if_engine will give true for all engines with the > exception of xetex + luatex? Even with etex or omega? Only three engines are supported: pdfTeX, XeTeX and LuaTeX, and even then only in sufficiently-new versions. The reason is ultimately that we need \pdfstrcmp or equivalent functionality. (expl3 will bail out if it can't find \pdfstrcmp, \strcmp or Lua to emulate it.) > In this case > it is what I'm after. But why does nobody use it? E.g. siunitx > contains > \xetex_if_engine:F { > \luatex_if_engine:F.... That code was written before \pdftex_if_engine: was added to expl3. I should alter it, I guess. -- Joseph Wright