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