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Message-ID:  <4C9905B4.2080802@morningstar2.co.uk>
Date:         Tue, 21 Sep 2010 20:21:24 +0100
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From: Joseph Wright <joseph.wright@MORNINGSTAR2.CO.UK>
Subject: Quarks: revisions of use in expl3
To: LATEX-L@listserv.uni-heidelberg.de
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Status: R

Hello all,

The documented use for different quarks in expl3 is broadly as follows:
  - \q_stop and \q_mark for delimiting arguments, with \q_stop used
    mainly
  - \q_nil as a nil pointer
  - \q_no_value to indicate the absence of a value at all

However, the use of these quarks in expl3 has been rather less well 
defined, with \q_nil in particular used in places where \q_stop is most 
appropriate. We've therefore revised the applications, and the SVN 
version of expl3 is now much more systematic in this regard.

In the main, this change should not affect the code others are using as 
these are mainly internal features. However, one place that the 
difference may impact is \tl_head:w and \tl_tail:w. These now terminate 
with \q_stop not \q_nil.

There will be a CTAN update of expl3 and xpackages soon (by the weekend, 
I hope). This will include these changes (along with others: see my 
other e-mails).
-- 
Joseph Wright