# File lib/openid/consumer/discovery.rb, line 243
  def self.find_op_local_identifier(service_element, type_uris)
    # Find the OP-Local Identifier for this xrd:Service element.
    # This considers openid:Delegate to be a synonym for xrd:LocalID
    # if both OpenID 1.X and OpenID 2.0 types are present. If only
    # OpenID 1.X is present, it returns the value of
    # openid:Delegate. If only OpenID 2.0 is present, it returns the
    # value of xrd:LocalID. If there is more than one LocalID tag and
    # the values are different, it raises a DiscoveryFailure. This is
    # also triggered when the xrd:LocalID and openid:Delegate tags are
    # different.

    # XXX: Test this function on its own!

    # Build the list of tags that could contain the OP-Local
    # Identifier
    local_id_tags = []
    if type_uris.member?(OPENID_1_1_TYPE) or
      # local_id_tags << Yadis::nsTag(OPENID_1_0_NS, 'openid', 'Delegate')
      service_element.add_namespace('openid', OPENID_1_0_NS)
      local_id_tags << "openid:Delegate"

    if type_uris.member?(OPENID_2_0_TYPE)
      # local_id_tags.append(Yadis::nsTag(XRD_NS_2_0, 'xrd', 'LocalID'))
      service_element.add_namespace('xrd', Yadis::XRD_NS_2_0)
      local_id_tags << "xrd:LocalID"

    # Walk through all the matching tags and make sure that they all
    # have the same value
    local_id = nil
    local_id_tags.each { |local_id_tag|
      service_element.each_element(local_id_tag) { |local_id_element|
        if local_id.nil?
          local_id = local_id_element.text
        elsif local_id != local_id_element.text
          format = 'More than one %s tag found in one service element'
          message = sprintf(format, local_id_tag)
          raise DiscoveryFailure.new(message, nil)

    return local_id