\useMPlibrary
  [dum]

\setupfloat
  [figure]
  [default=top]

\ctxlua{structures.lists.autoreorder = true}

\starttext

\input knuth

alpha: \in{figure}[alpha] \par
beta:  \in{figure}[beta]  \par
gamma: \in{figure}[gamma] \par

\startplacefigure [title=Alpha, reference=alpha]
  \externalfigure [dummy]
\stopplacefigure

\startplacefigure [title=Beta, reference=beta]
  \externalfigure [dummy] [width=10cm, height=16cm]
\stopplacefigure

\startplacefigure [title=Gamma, reference=gamma]
  \externalfigure [dummy]
\stopplacefigure

\stoptext
