return the content of the XML document as a unicode string

def tostring(self, root=None, doctype=None, pretty_print=True):
        """return the content of the XML document as a unicode string"""
        if root is None:
            root = self.root
        return etree.tounicode(
            root, doctype=doctype or self.info.doctype, pretty_print=pretty_print
        )