Thanks Hans, for the fast response.
On 27-aug-2006, at 14:56, Hans Hagen wrote:

\disablemode[xml:linebreak]


\startsetups[xml:linebreak]

  \doifmode{xml:linebreak}{\disablemode[xml:linebreak]\crlf}  

\stopsetups 


\defineXMLenvironment [av] {} {\ensablemode[xml:linebreak]}


\defineXMLenvironment [liste] {\setups[xml:linebreak]} {\crlf}


or sometign similar,  


I have played around with this solution for a bit and \defineXMLenvironment [liste] {} {\setups[xml:linebreak]}
 seems to work for the <liste>-tag. But it not entirely clear to me how this should work for the <av>-tag when it is not followed by another tag on the same line. 

Sjoerd