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Date:         Sun, 2 Jan 2011 20:23:11 +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
In-Reply-To:  <473826.54913.qm@web82001.mail.mud.yahoo.com>
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Status: R

On 02/01/2011 15:27, Paul Thompson wrote:
> There is really a somewhat deeper issue.  Like many who use LaTeX for more than
> superficial stuff (I wrote a class file newlfm and several sty files, most of
> which are not much used), I can read documentation and figger it out somewhat.
> However, knowing of the EXISTENCE of a tool is really the key, not how it is
> used.  How are people to learn that specific primitives exist?  It's not in the
> LaTeX Companion, which is my starting point.

As Arno has already commented, this is a primitive, so it belongs in the 
pdfTeX manual and not in anything from LaTeX. I'd also note that it was 
introduced relatively recently (compared at least to the age of 
LaTeX2e), so it's not surprising that it's not there.

As an aside, one of the points of the expl3 work is to provide a LaTeX 
programming language in which everything is documented if it's 
available. That doesn't mean that all of the primitives are documented 
in expl3: the other point is that many of them are not really ideal for 
direct use. \pdfstrcmp is a case in point: the expl3 interface is called 
\str_if_eq:xxTF (and related functions), as it's not excatly obvious 
that a string comparison yields a number which can then be used in an 
\ifnum :-)
-- 
Joseph Wright