Iterator is a simple transform that selects the XML nodes that satisfies an XPath/XSL node expression. Each selected node is sent as the output document to the output port.
Prior to sending any selected nodes to the output port, a <cx:begin> control document is sent on the output port. And, after sending all selected nodes to the output port a <cx:end> control document is sent to the output port and a signal is sent on the done pin.
For further information on XPath/XSL expressions, see XSL references.