[NTG-context] In need of more detailed widget descriptions!

Hi, I'm struggling with widgets and went already through the Widget Uncovered manual, but experience problems running various examples under MkIV! MAIN QUESTION: Is the manual still valid for MkIV? When I use for example the command \tracefieldstrue an Undefined control sequence error is triggered! ADDITIONAL QUESTION: Is it possible to give a simple example on how to write a validation function using JavaScrip or Lua? I already looked at the module m-fields.mkiv but I still do need some additional explanation on that, sorry! Regards, Gerard Verhaag P.S. Use ConTeXt ver: 2011.05.16 11:00 MKIV