Why not, if all else fails, do a run of the completed matter to see what
the pagination would be, then do something like:

\newif\ifhidden

% Uncomment this if you want to hide content.
% \hiddentrue

\ifhidden
 % . . . preferrably use ConTeXt-friendly pagination
 % commands; this was taken from a plain old TeX file.
 % Shove in white space or \phantom{} boxes with dummy text of
 % equivalent length; ConTeXt likes its own \blank{} macro.
 % Raw TeX stuff can mess up pagination and spacing.
 %
 % I'm not sure if a \vbox to <dimen> {} works well or not here.
 % Just try a few ways to see.
\else
 % Put all your usual content here.
\fi

It's a kludge, but it should work in a pinch.

Charles

On Thu, 2008-07-24 at 15:21 +0200, Alan Stone wrote:
> >And you want to hide part of the content for ...
>
> Enabling people to view the pdf preview version (limited, containing
> excerpts) before acquiring the full version.
>
> Alan
>
> On Thu, Jul 24, 2008 at 3:03 PM, Wolfgang Schuster
> <schuster.wolfgang@googlemail.com> wrote:
>         On Thu, Jul 24, 2008 at 2:34 PM, Alan Stone
>         <software.list.1es9s@gmail.com> wrote:
>
>         > I understood from this post
>         >
>         http://archive.contextgarden.net/message/20050708.105010.33153980.en.html
>         > there were issues with the different solutions offered.
>
>
>         You should give it a try, a few of the points concerned
>         security reasons and
>         old version of Acrobat Reader, there is also a wiki page about
>         this topic.
>
>         http://wiki.contextgarden.net/Hiding_Content
>
>         >>Do you want to hide only text or also figures, tables,
>         formulae etc.
>         >
>         > For the time being there's only text, however in a later
>         stage there will be
>         > figures/pics too.
>         >
>         >>do you need a solution that
>         >>will work also over page breaks.
>         >
>         > Yes, to make a preview version of a book.
>
>
>         And you want to hide part of the content for ...
>
>
>
>         Wolfgang
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