docs: def dump(self, stream):
          """
          Dumps the data to stream after appending header.
          """
          if self.prettyprint:
              self.indent(self.xml)
          document = etree.ElementTree(self.xml)
          header = '<?xml version="1.0" encoding="%s"?>' % self.encoding
          stream.write(header.encode(self.encoding))
          document.write(stream, encoding=self.encoding)