I made use of descriptions in mkii. For example:
% Define the intro for the annotation
% Block opened on \startquestion and closed on \stopquestion
% \startannotation{} ... \stopannotation; {} required
\definedescription[annotationblock][%
\c!margin=\v!no,\c!location=\v!top,\c!width=\v!broad,%
\c!headstyle=\@@exmintrostyle,\c!style=\@@exmstyle,%
\c!before=,\c!inbetween=,\c!after=,%
\c!text=\placeannotationstart]
etcetera

The error message in latest context beta is:

! Use of \@@startdescription doesn't match its definition.
\doifnextoptionalelse ...\nextoptionalcommandyes {
                                                  #1}\def \nextoptionalcomma...
\setuptextrules ...odoubleargument \getparameters 
                                                  [\??tl ]
\placeannotationstart ...aloffset \setuptextrules 
                                                  [\c!style =\@@exmintrostyl...
\dododescriptioncomponent ...onparameter \c!label 
                                                  }\xdef \currentdescription...
\@@makedescription ...},\c!bookmark =,\c!list =][]
                                                  \@@dostartdescriptionindeed 
\dodogotopar ->\@@makedescription []{}
                                      \BeforePar \emptytoks 
...

Can someone tell me if it is known to be broken in mkiv? Before delving too deep in the code myself....

Hans van der Meer