[NTG-context] pdfobj runtime question

hi, i'm currently struggling with some basic runtime problems in luatex. are there any rules for directly writing a pdf object? in context this is only done in the tex part. especially what pitfalls are there, if you do it in the lua part of the code ( tex.sprint(tex.ctxcatcodes,"\\immediate\\pdfobj{}")) ) and use "\the\pdflastobj" (tex or lua) to reference that object? and what must be done to make sure that things are done immediatly (in lua), so that one ore more switches between lua<-->tex always uses the right obj number? i already noticed that you have to use separated lua code for 'creation' and 'reference' (different chunks). any help welcome. regards, peter