I see.  Thanks for the explanation.

So the following works:

-------------------------------
\unprotect
\setvalue{startNotes}%
  {\global\settrue\c_page_comment_enabled
   \grabbufferdatadirect{pagecomment}{startpagecomment}{stopNotes}}
\protect
\def\stopNotes{}
------------------------------

What does the second argument to \grabbufferdatadirect mean?  Nothing
changes when I modify that.

The point of redefining the pagecomment environment for me was to style it
a bit: add \righttoleft at the beginning, and surround the content in
startstopnarrower.  How can I inject prepend/append to a buffer's content?

The solution I can think of is to use a different buffer
"pagecomment_internal" in the above definition, and then build buffer
"pagecomment" using that.

Thanks,
~MHB

On Sat, Apr 27, 2019 at 1:24 AM Wolfgang Schuster <
wolfgang.schuster.lists@gmail.com> wrote:

> Mohammad Hossein Bateni schrieb am 27.04.2019 um 05:16:
> > Hi,
> >
> > Look at the following MWE:
> >
> >
> > \setuppagecomment[state=start,location=right]
> > %\definestartstop[Notes]
> > %[before=\startpagecomment,after=\stoppagecomment]
> > \def\startNotes{\startpagecomment}
> > \def\stopNotes{\stoppagecomment}
> >
> > \starttext
> > \input knuth
> > \startpagecomment
> > Hello
> > \stoppagecomment
> > \page
> > \input tufte
> > \startNotes
> > Testing
> > \stopNotes
> > \stoptext
> >
> >
> > This snippet does not compile.  Page comments work when I use the
> > commands \startpagecomment and \stoppagecomment directly (like in the
> > first page), but when I invoke via macros (as in the second page),
> > ConTeXt produces errors.
> >
> > What is wrong there?
>
> The pagecomment environment uses the buffer mechanism to store the content
> of the environment but a limitation of buffers is that you can't put
> them into other
> commands because the scan for a certain delimiter, e.g. \stoppagecomment.
>
> Wolfgang
>
>