Parallel loop iterator

[Garry_Galler]

> `||` - parallel loop iterator. Same as .. but the loop may run in parallel.

Can anybody explain what kind of parallelism is here meant? And how is it 
supposed to work? In the example below, it works in series. 
    
    
    import strutils
    
    var x=0
    for i in 1||1000:
      inc x
      echo "[$1]=$2" % [$i,$x]