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Date:         Mon, 2 Jan 2012 14:27:52 +0000
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From: Joseph Wright <joseph.wright@MORNINGSTAR2.CO.UK>
Subject: Re: \leavevmode?
To: LATEX-L@listserv.uni-heidelberg.de
In-Reply-To:  <1ngcr82t9io26$.dlg@nililand.de>
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Status: R

On 31/12/2011 11:51, Ulrike Fischer wrote:
> Well I thought about 
> 
>   \hbox_unpack_clear:N\c_empty_box  
> 
> (as the documentation of source3 says that \hbox_unpack_clear:N is
> \unhbox).
> 
> And as I can see l3galley uses 
> 
>   \tex_unhbox:D \c_empty_box.
> 
> Is there any real difference between the three variants?

Must be an older version of l3galley: that version is not in the SVN.

As you say, \hbox_unpack_clear:N = \unhbox while \hbox_unpack:N =
\unhcopy. I'd prefer the latter as nothing should be modifying a
constant (\c_...), even though here it would make no difference.

Both primitives \unhbox and \unhcopy do what is needed here, so there is
no difference in terms of outcome.

> And is the name in l3galley "\galley_leave_vmode:" stable? I would
> prefer a standard command instead of my own local
> \leavemode-command. \leavemode is imho such a central concept that
> it should have a standard name. 

There are two slightly separate concepts here (I think - Frank may
correct me). One is the need in the galley mode to leave vertical mode,
and the other is the more general case of 'some arbitrary command'. The
galley has to work a particular way, and it therefore may on occasion do
it's own thing. So I suspect that \galley_... is not the right place for
a general 'ensure we are not in vertical mode' function.

That leaves the question of where /is/ the right place. One obvious
suggestion is \mode_leave_vertical: or \mode_ensure_not_vertical: (the
latter is a bit awkward if more accurate).
-- 
Joseph Wright