Add a new element @elem to the list of siblings of @cur
          merging adjacent TEXT nodes (@elem may be freed) If the new
          element was already inserted in a document it is first
           unlinked from its existing context.

def addSibling(self, elem):
        """Add a new element @elem to the list of siblings of @cur
          merging adjacent TEXT nodes (@elem may be freed) If the new
          element was already inserted in a document it is first
           unlinked from its existing context. """
        if elem is None: elem__o = None
        else: elem__o = elem._o
        ret = libxml2mod.xmlAddSibling(self._o, elem__o)
        if ret is None:raise treeError('xmlAddSibling() failed')
        __tmp = xmlNode(_obj=ret)
        return __tmp