This is not the same as  [eval] 

 [dup]  evaluates the content once and then duplicates it N times;  [eval]  can call a style and re-evaluate it on every iteration, passing the content to the style.

As interation and nesting depth of iterations can both create large amounts of output, both may be limited by the invocation parameters xlimit and dlimit. See this page for details on how to set those for class invocations.