On Mon, Sep 30, 2013 at 6:00 PM, luigi scarso <luigi.scarso@gmail.com>wrote:

>
>
>
> On Mon, Sep 30, 2013 at 5:38 PM, Lars Huttar <lars_huttar@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