[NTG-context] getdocumentargument in Metafun

Dear list, I wish to do several zoom from a picture made in MetaFun, from a pdf file which name is given on the commande line, like: context zoom.tex —File=EntryFile —Page=9 —result=OutFile.pdf Minimal example: \starttext \startMPpage numeric ThePage ; string FileName ; FileName := \getdocumentargument{File} ; ThePage := \getdocumentargument{Page} ; draw textext("\externalfigure[" & FileName &"][page=" & ThePage &"]") xysized (48in,48in) ; \stopMPpage \stoptext I can get in the MPpage the page number in entry (9 in my example), but not the file name. Thanks for any help. Fabrice.