nothing ... handling text is then up to the calling applications; from the perspective of mp text is just a picture or whatever else it can manipulate
Does your already running instance of TeX (LuaTeX and mkiv) handles the job of typesetting the labels? Even if this is completely disconnected from the flow of the document currently processed?
well, did you try it? the mpost related code in mkiv does the labels (there is/will be an article on how that is done in a couple of tex user group journals); so ... in context/mkiv no tex runs inside tex runs unless you do somethign real tricky like graphictext which needs to pipe pdf code into pdtoedit
Many thanks Hans for your explanations. I was just curious how things worked because there are a lot of user applications that would benefit from on the fly typesetting on a single page (a vbox). Olivier