def fetch_command_target(exp=parent)

      case exp
        when nil then nil
        when Ruote::Exp::CommandedExpression then exp
        else fetch_command_target(exp.parent)
      end
    end
def fetch_command_target(exp=parent)

      case exp
        when nil then nil
        when Ruote::Exp::CommandedExpression then exp
        else fetch_command_target(exp.parent)
      end
    end
Walks up the expression tree (process instance and returns the first
 expression that includes the CommandMixin

 (CommandExpression includes CommandMixin, but since it doesn't have
 children, no need to 'evince' it)