Domain crossing: how much expertise is enough?

In CSCW, how much do we need to know about another domain/culture before we observe, intersect and intervene with designs. What optimally would that other culture need to know about us? Is this a “how long is a piece of string” question, or an inquiry where we can consider a variety of contexts and to explicate best practice. The goal of this panel will be to develop heuristics for such practice