A SerializationHandler accepts SAX-like events, so it can accumulate attributes or namespace nodes after a startElement().
If the SerializationHandler has a Writer or OutputStream, a call to this method will flush such accumulated events as a closed start tag for an element.
If the SerializationHandler wraps a ContentHandler, a call to this method will flush such accumulated events as a SAX (not SAX-like) calls to startPrefixMapping() and startElement().
If one calls endDocument() then one need not call this method since a call to endDocument() will do what this method does. However, in some circumstances, such as with document fragments, endDocument() is not called and it may be necessary to call this method to flush any pending events.
For performance reasons this method should not be called very often.