@morrisonlevi Please don't assume what I do and do not know. The base Iterator interface provides no way to modify the iterator: http://www.php.net/manual/en/class.iterator.php. Yes, PHP has more iterator interfaces. That doesn't make it a good use case for message bodies. Show me how iterators support what you call "concatenate" without a custom solution or using something like AppendIterator or using ArrayIterator and setting a new index after getting the count of the Iterator (thus forcing implementations to support far more than what's relevant to message bodies). Message bodies aren't just used for reading; there has to be a good way to  write to them.