[NTG-context] margin of inner item group

Dear List, Does anyone know how to set the margin of an inner item group? The natural way does not seem to work: \showframe \starttext \startitemize[margin=5em] \item 1 \startitemize[margin=10em] \item 1 \item 2 \item 3 \stopitemize \item 2 \item 3 \stopitemize \stoptext In the doc above, only the outer item group has a margin. Any help will be appreciated. Best, Sylvain