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)



-- 
luigi