I'm trying to extract pages from an existing pdf using lua.
But this approach to extract pages 11 and 30 does not work:

\starttext
\startluacode
for i, blz in ipairs({11, 30}) do
  context.startTEXpage()
  context.externalfigure("my_pdf.pdf", page=blz)
  context.stopTEXpage()
end
\stopluacode
\stoptext


Where am I missing the point?

.F