Caution:

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.

[local x 0]
[dup 5,foo[vinc x] ]
----
[style binky [b][vinc x] ]
[local x 0]
[eval style=binky,5,bar]

foo1 foo1 foo1 foo1 foo1
----
bar1 bar2 bar3 bar4 bar5

foo1 foo1 foo1 foo1 foo1 ---- bar1 bar2 bar3 bar4 bar5

Note:

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.