[NTG-context] Multiple Footnote Threads

Hello, Using ConTeXt, I would like to have multiple footnote threads in a document. For example, one thread might be for the reader, another for a particular reviewer, and another for my own editing notes or comments forrequired future work. Each thread should be indexed by a different set of symbols, and placed at the bottom of the page or at the end of the text or document as desired. I have found this to be a good way to work. However, I can't find a way to do this in ConTeXt. Does anyone have any ideas? Thanks in advance, Rob Walton