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Date:         Sat, 1 Jan 2011 19:32:21 +0000
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From: Joseph Wright <joseph.wright@MORNINGSTAR2.CO.UK>
Subject: Re: LaTeX3 and engines
To: LATEX-L@listserv.uni-heidelberg.de
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Status: R

On 01/01/2011 18:17, TeXWorld wrote:
> Hello,
>
> What engines LaTeX3 is (and will be) designed to work with ? Like
> LaTeX2e it will work with TeX, PDFTeX, XeTeX, LuaTeX, (Aleph...???), or
> with a more limited list such as LuaTeX and XeTeX ? I'd like to know if
> a decision has been taken and whether it has, I'd like to know why such
> a decision.
>
> Thank you.
>
> Jack
>

Hello Jack,

I think a bit of history is needed here. At first, the only primitives 
that expl3 *required* were those from TeX82 (Knuth's TeX). Some years 
ago now, it was decied to require the e-TeX extensions. These allow a 
number of functions to be carried out which are difficult or impossible 
otherwise. More recently, we have added \pdfstrcmp to the list of 
required primitives. This primitive allows expandable string-based 
comparisons, which are important for some low-level expl3 functions. So 
the requirement at present is a TeX engine which includes the e-TeX 
extensions and the functionality of \pdfstrcmp. This means the following 
engines should work:

  - pdfTeX v1.30 or later
  - XeTeX v0.9994 or later
  - LuaTeX v0.40 or later

As LaTeX3 is far from ready, this may change in the future. However, the 
team have always been relatively cautious about engine requirements, and 
I expect that the above will remain as the minimum engine list for some 
time to come. (With LuaTeX, I'd strongly recommend a newer engine, given 
the pace of development of the binary. I'd *suggest* at least 0.60.)

Joseph Wright