Returns the child node of the receiver at the specified location.
- macOS 10.4+
An integer specifying a node position in the receiver's array of children. If
indexis out of bounds, an exception is raised.
An NSXMLNode object or
nil f the receiver has no children.
The receiver should be an
NSXMLNode object representing a document, element, or document type declaration. The returned node object can represent an element, comment, text, or processing instruction.