code: def emit_head(self, stream_from, stream_to, stream_id = None,
                                              version = u'1.0', language = None):
          
          # pylint: disable-msg=R0913
          self._root_prefixes = dict(STANDARD_PREFIXES)
          self._root_prefixes[self.stanza_namespace] = None
          for namespace, prefix in self._root_prefixes.items():
              if not prefix or prefix == "stream":
                  continue
              if namespace in STANDARD_PREFIXES or namespace in STANZA_NAMESPACES:
                  continue
              self._root_prefixes[namespace] = prefix
          tag = u"<{0}:stream version={1}".format(STANDARD_PREFIXES[STREAM_NS],
                                                          quoteattr(version))
          if stream_from:
              tag += u" from={0}".format(quoteattr(stream_from))
          if stream_to:
              tag += u" to={0}".format(quoteattr(stream_to))
          if stream_id is not None:
              tag += u" id={0}".format(quoteattr(stream_id))
          if language is not None:
              tag += u" xml:lang={0}".format(quoteattr(language))
          for namespace, prefix in self._root_prefixes.items():
              if prefix == "xml":
                  continue
              if prefix:
                  tag += u' xmlns:{0}={1}'.format(prefix, quoteattr(namespace))
              else:
                  tag += u' xmlns={1}'.format(prefix, quoteattr(namespace))
          tag += u">"
          self._head_emitted = True
          return tag
docs: Return the opening tag of the stream root element.
  
          :Parameters:
              - `stream_from`: the 'from' attribute of the stream. May be `None`.
              - `stream_to`: the 'to' attribute of the stream. May be `None`.
              - `version`: the 'version' of the stream.
              - `language`: the 'xml:lang' of the stream
          :Types:
              - `stream_from`: `unicode`
              - `stream_to`: `unicode`
              - `version`: `unicode`
              - `language`: `unicode`