function startBrowserTracingNavigationSpan(client, spanOptions) {
  if (!client.emit) {
    return;
  }

  client.emit('startNavigationSpan', spanOptions);

  const span = core.getActiveSpan();
  const op = span && core.spanToJSON(span).op;
  return op === 'navigation' ? span : undefined;
}
Returns the value of a meta tag