XMLString :: close - Close XML string
No value returned.
Implementation details
XMLString  :: close (  )
When the XMLString is the top string, The destructor completely destroys the XMLString. Because subordinated elements are note automatically de-referenced, accessing those after deleting the top XMLString will cause system exceptions.
When destroying a subordinated element, only the reference in the XMLString will be reset.
After closing the XMLString, it becomes invalid.