[xml] Thread safety of libXML2?

[David Hagood <wowbagger sktc net>]

Assume that I have a single xmlSaveCtxtPtr that has been created, and is
visible to multiple threads within a program.

Assume that I have multiple threads creating multiple document fragments
(separate xmlNodePtr objects, one per thread), using various xmlNewChild
and the like calls. Assume that only one thread manipulates any given
xmlNodePtr.

Is the call to xmlSaveTree intrinsically thread safe, or do I have to do
my thread protection outside of xmlSaveTree?