On Mon, Sep 30, 2013 at 6:00 PM, luigi scarso <luigi.sca...@gmail.com>wrote:
>
>
>
> On Mon, Sep 30, 2013 at 5:38 PM, Lars Huttar <lars_hut...@sil.org> wrote:
>
>> I found \start and \stop referenced in the context reference manual
>> (e.g. section 5.5).
>> While \startXYZ - \stopXYZ pairs are discussed earlier, I can't find any
>> place that \start and \stop (with no suffix) are described.
>> They seem to be used like \bgroup and \egroup. Is that right?
>> They are defined in core-sys.mkiv, but I can't figure out from there
>> what they actually do.
>>
>> I'll contribute documentation for them if someone can tell me what they
>> mean.
>>
>> Thanks,
>> Lars
>>
>
>
>
>
> core-sys.mkiv :
>
>
> \unexpanded\def\start
> {\dosingleempty\syst_start}
>
> \def\syst_start
> {\bgroup
> \iffirstargument
> \expandafter\syst_start_yes
> \else
> \expandafter\syst_start_nop
> \fi}
>
> \def\syst_start_yes[#1]%
> {\edef\m_syst_start_stop{#1}%
> \ifx\m_syst_start_stop\empty
> \let\syst_stop_indeed\donothing
> \else\ifcsname\e!start\m_syst_start_stop\endcsname
>
> \expandafter\let\expandafter\syst_stop_indeed\csname\e!stop\m_syst_start_stop\endcsname
>
> \csname\e!start\m_syst_start_stop\expandafter\expandafter\expandafter\endcsname
> \else
> \let\syst_stop_indeed\donothing
> \fi\fi}
>
> \def\syst_start_nop[#1]%
> {\let\syst_stop_indeed\donothing}
>
> \unexpanded\def\stop
> {\syst_stop_indeed
> \egroup}
>
>
> (it should be \let\donothing\empty)
>
> sorry, hit return too early.
\start <...> \stop without argument is
\bgroup % from\def\syst_start
\expandafter\syst_start_nop
\syst_start_nop is
{\let\syst_stop_indeed\donothing}
and \stop is hence
\syst_stop_indeed
\egroup
i.e.
\donothing
\egroup
are like \bgroup <...> \egroup
It seems that there are no examples of \start[]<..>\stop .
--
luigi
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