This is useful for, e.g., typesetting bilingual books: have the original on the even pages, the translation on the odd pages, and synchronize at certain points.
Hans later re-implemented that mechanism in the core. For details see [[source:mpage-streamsstr.texmkiv|streams module the source]].
The module provides a rather low-lever interface. Hans suggested some handy shortcuts:
Beware, streams don't work in columns and not very good in columnsets.
==Example of MkIV streams==
(copied from the source)
<texcode>
\enabletrackers[streams.flushing]
\setuplayout[grid=yes] \showgrid
\starttext
\input tufte
\startoutputstream[nl]
Wat doen we hier?
\enableoutputstream[en]
Are you sleeping, brother John?\footnote{xxx}
\dorecurse{4}{x \footnote{note \recurselevel}\input tufte \par \pushoutputstream}
\enableoutputstream[de]
Bruder Jakob, schläfst du noch?\footnote{yyy}
\dorecurse{4}{x \footnote{note \recurselevel}\input ward \par \pushoutputstream}
\disableoutputstream
\stopoutputstream
Vader Jacob, slaap je nog?\footnote{zzz}
\input tufte
\synchronizestreams[en,de,nl]
\page \flushoutputstream[en] \input knuth
\page \flushoutputstream[de] \input knuth
\page \flushoutputstream[nl] \input knuth
\stoptext
</texcode>
{{todo|We need documentation and samples for Paragraphs, Streams and Column Sets}}