My example is setup as advised in the manual:

"""
%\mainlanguage[de]
\usebtxdataset[beispiel][bib_example.bib]
\setupbtx[dataset=beispiel]
%\usebtxdefinitions[apa]
\definebtxrendering[beispiel][apa][dataset=beispiel,group=beispiele]

\starttext
\placelistofpublications[beispiel]

\cite[authoryear] [WiFo2010]

\cite[authoryear] [rattenhka]

\stoptext
"""

But I get the error message:

"""
system          > error: invalid parent apa for beispiel, apa defined 
too (best check it)
system          > error: invalid parent btx:apa for btx:beispiel, 
btx:apa defined too (best check it)
"""

Are these messages wrong? And why do they come from "system" and not 
from "publications"?


My minimal example works anyway, still investigating why it doesn’t in 
my book.


Another question:

Consider:
@Book {rattenhka,
author = "Bettina von Arnim and Gisela von Arnim",
title = "Das Leben der Hochgräfin Gritta von Rattenzuhausbeiuns",
…
}

The authors are usually given as “Bettina and Gisela von Arnim” (mother 
and daughter; similar “Jacob and Wilhelm Grimm” as brothers or “Bettina 
and Achim von Arnim” as a couple) – is there a good solution for related 
authors?

Hraban