code: func (builder *SSMLTextBuilder) AppendProsody(text, rate, pitch, volume string) *SSMLTextBuilder {
  
  	builder.buffer.WriteString(fmt.Sprintf("<prosody rate=\"%s\" pitch=\"%s\" volume=\"%s\">%s</prosody>", rate, pitch, volume, text))
  
  	return builder
  }
docs: // AppendProsody provides a way to modify the rate, pitch, and volume of a piece of spoken text.