\startbuffer[first]

    @article {one,
        title  = "Article One",
        author = "Author, One",
        year   = 2015,
    }

    @article {two,
        title  = "Article Two",
        author = "Author, Two",
        year   = 2015,
    }

\stopbuffer

\startbuffer[second]

    @article {alpha,
        title  = "Article Alpha",
        author = "Author, Alpha",
        year   = 2015,
    }

    @article {beta,
        title  = "Article Beta",
        author = "Author, Beta",
        year   = 2015,
    }

\stopbuffer

\startbuffer[third]

    @article {foo,
        title  = "Article Foo",
        author = "Author, Foo",
        year   = 2015,
    }

    @article {bar,
        title  = "Article Bar",
        author = "Author, Bar",
        year   = 2015,
    }

\stopbuffer

\usemodule
  [article]

\definebtxdataset [first]
\definebtxdataset [second]
\definebtxdataset [third]

\usebtxdataset [first]  [first.buffer]
\usebtxdataset [second] [second.buffer]
\usebtxdataset [third]  [third.buffer]

\definebtxrendering [first]  [dataset=first, criterium=text,specification=default]
\definebtxrendering [second] [dataset=second,criterium=text,specification=default]
\definebtxrendering [third]  [dataset=third, criterium=text,specification=default]

\defineregister[indexofauthors]

\definebtxregister
  [authors-1]
  [field=author,
   register=indexofauthors,
   method=always,
   dataset={first,second,third},
   alternative=invertedshort]

% \definebtxregister
%   [authors-2]
%   [authors-1]
%   [dataset=second]

% \definebtxregister
%   [authors-3]
%   [authors-1]
%   [dataset=third]

\starttext

    \setupbtxlist[default][prefix=yes,width=1cm]

    \cite[crap]
    \cite[match(author:crap)]

    \startsection[title=first]
        from first  we take \cite[first::one]    and \cite[first::two]   \blank[big]
    \stopsection
    \startsection[title=second]
        from second we take \cite[second::alpha] and \cite[second::beta] \blank[big]
    \stopsection
    \startsection[title=third]
        from third  we take \cite[third::foo]    and \cite[third::bar]   \blank[big]
    \stopsection

    \startsection[title=lists]
        \startpacked \placebtxrendering [first]  \stoppacked \blank[big]
        \startpacked \placebtxrendering [second] \stoppacked %blank[big]
        \startpacked \placebtxrendering [third]  \stoppacked \blank[big]
    \stopsection

    \page

    \placeregister[indexofauthors]

\stoptext
