xmlSaveFile is available since version 1.0.
Prototype:
number xmlSaveFile(string filename, number doc)
Parameters
filename
the filename (or URL)
doc
the XML document handle
Description:
Dump an XML document to a file. Will use compression if compiled in and enabled. If filename is "-" the stdout file is used.
Return value:
Returns the number of bytes written or -1 in case of failure.