8

Here is the very simple MWE:

% Plain
\number\eTeXversion\eTeXrevision
\bye

But the results differ by TeX engine (in TeX Live 2018):

pdfTeX, XeTeX: 2.6

LuaTeX: 2.2

Considering only e-TeX extensions, is there any difference between LuaTeX and eTeX/pdfTeX/XeTeX?

13

LuaTeX was developed starting from the pdfTeX codebase (though the two are now very different). At the time of the split, the e-TeX release was v2.2, and so this is what LuaTeX reports. Subsequently, further work took place with e-TeX:

% Version 2.3 development was started in Feb 2008; released in Apr 2011.
%             fixed a bug in hyph_code handling (\savinghyphcodes)
%                 reported by Vladimir Volovich <vvv@@vsu.ru>, Feb 2008.
%             fixed the error messages for improper use of \protected,
%                 reported by Heiko Oberdiek
%                 <heiko.oberdiek@@googlemail.com>, May 2010.
%             some rearrangements to reduce interferences between
%                 e-TeX and pTeX, in part suggested by Hironori Kitagawa
%                 <h_kitagawa2001@@yahoo.co.jp>, Mar 2011.
% Version 2.4 fixed an uninitialized line number bug, released in May 2012.
% Version 2.5 development was started in Aug 2012; released in Feb 2013.
%             better tracing of font definitions, reported by
%                 Bruno Le Floch <blflatex@@gmail.com>, Jul 2012.
% Version 2.6 development was started in Mar 2013; released in ??? 201?.
%             enable hyphenation of text between \beginL and \endL or
%                 between \beginR and \endR, problem reported by
%                 Vafa Khalighi <vafalgk@@gmail.com>, Nov 2013.
%             better handling of right-to-left text -- to be done.

Notably, there are no new features in the changes: they are mainly 'internal' alterations. This work was merged into pdfTeX (and XeTeX and e-(u)pTeX) as they remain coded in WEB. In contrast, LuaTeX is now written in C /CWEB, and so a direct merge is not possible. Also, LuaTeX development has addressed many of the same issues in different ways: most notably, LuaTeX does not use TeX--XeT at all.

  • 2
    It's quite unfortunate that the manual for e-TeX doesn't mention the changes. – egreg May 7 '18 at 11:08
  • @egreg I think there are no API changes – Joseph Wright May 7 '18 at 11:10

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