Thanks Hraban, this is exactly what I need! Once more, the stuff I was looking for was already implemented in ConTeXt…

Am 07.12.24 um 13:57 schrieb Damien Thiriet via ntg-context:

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In French typography, roman numerals are usually typeset being connected with a top bar and a lower bar

Did you try the numbering option "or"?

\convertnumber{or}{12}

Hraban

Damien