How to do that in the ConTeXt way ? ;) I have read spec-tpd.tex but didn't know much...
indeed pdfannot is what we need; however, the first thing is to figure out what kind of control we want (probably best from within javascript); in your sampe i see pretty raw pdf code in the key/val pairs, which is something alien to context - what features make sense - what features do we expect to be stable Hans