xmlDoc is a special case of
xmlNode. Each XML
document has a single
xmlDoc that is that the root of the
document. It can be used in many of the same functions as
xmlNode's (such as
xmlTreeGetChildren()), but also contains
document-wide information, such as character encoding.
xmlDoc's can be saved to a file and converted to strings with the
xmlTreeSaveDoc() (here) and
xmlTreePrintDoc() (here) functions,
Also see the
xmlDoc vs. Root Element section
(here) for details on the differences between
xmlDoc's and the root element of a document.