      \fitem{make_duration_map}() \emph{or} (start:numeric) \emph{or}
      (start:numeric, stop:numeric): \\ %%
      \code{@make_duration_map(a, b)} returns a map where the duration (in beat)
      of the $i$th event of the score, is associated to $i$ (the keys of
      the map are the ranks of the events). 
      %% 
      Called with no arguments, the events considered are all
      the events in the score. With \code{start}, only the events whose
      position is greater than \code{start} are considered. If a
      \code{stop} is specified, all events must have a position between
      \code{start} and \code{stop}.

      %%% -------------------------------------------------------


