[NTG-context] Slides: uncover things piecewise

Hi,

I use the »simpleslides« module for a presentation and I wonder if it is
possible to uncover things piecewise. Take the following example:

\usemodule [simpleslides]
\starttext
\SlideTitle {My Topic}
\startitemize
\item First  % Visible by default
\item Second % Gray by default
\item Third  % Gray by default
\stopitemize
\stoptext

I want to achieve the following: The first item should be visible by
default. The second and third items are not visible or grayed out. The by
jumping to the (physically) next slide (for the audience it's still the
same page) the second item will be displayed and so on...

I've found some old pieces of code in the mail archive but didn't get it to
work.

Kind regards
Marco

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