code: func (t *Tracer) StartSpanFromContext(ctx context.Context, name string, options ...SpanOption) (Span, context.Context) {
  	if parentSpan := SpanFromContext(ctx); parentSpan != nil {
  		options = append(options, Parent(parentSpan.Context()))
  	}
  	span := t.StartSpan(name, options...)
  	return span, NewContext(ctx, span)
  }
docs: // StartSpanFromContext creates and starts a span using the span found in
  // context as parent. If no parent span is found a root span is created.