[NTG-context] references to external documents

Hi all! I'm working with huge XML documents which are compiled to PDF (with ConTeXt) and converted to HTML (with XSLT and others). These XML documents contain references to external files (images). References are mapped to paths with XML code; i.e. <imgref id="cow" src="./images/cow.png"/>. Translating such a map to ConTeXt is rather obvious. But how to implement simmilar mechanism for external XML documents? In example I would like to use command \useexternaldocument[intro][introduction.xml] and than process 'introduction.xml' on the base of is ID reference ('intro'). Is it possible? Does ConTeXt suport referencing documents as well as figures? Regards, Pawe/l