[NTG-context] How to debug XML processing

Hello, After reading "Getting Web Content and pdf-Output from One Source" by Thomas A. Schmitz, i'm trying to use the same method to build a PDF file from a HTML one. But i quickly found that when something doesn't work as expected, it's pretty hard to debug because it's hard to tell if the error come from the environment file, the lua code or something else. So are there some useful tricks to debug this kind of processing besides the \enabletrackers command? Especially is there a way to view the generated ConTeXt code after the macro expansion? Thank you. Regards, Stéphane.