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Technical Overview
  public package Foswiki::AggregateIterator  is a Foswiki::Iterator 
implements Foswiki::Iterator
Combine multiple iterators into a single iteration.
 new(\@list, $unique) 
Create a new iterator over the given list of iterators. The list is
not damaged in any way.
If 
$unique is set, we try to not repeat values.
Warning: 
$unique assumes that the values are strings.
 hasNext() → $boolean 
Returns false when the iterator is exhausted.
 next() → $data 
Return the next entry in the list.
The iterator object can be customised to pre- and post-process entries from
the list before returning them. This is done by setting two fields in the
iterator object:
 
-  {filter}can be defined to be a sub that filters each entry. The entry     will be ignored (next() will not return it) if the filter returns false.
-  {process}can be defined to be a sub to process each entry before it     is returned by next. The value returned from next is the value returned     by the process function.