code: func NewDecoder(opts *DecoderOptions) *Decoder {
  	dec := &Decoder{opts: opts}
  	if dec.opts == nil {
  		dec.opts = &DecoderOptions{}
  	}
  	if dec.opts.TagName == "" {
  		dec.opts.TagName = tagName
  	}
  	return dec
  }
docs: // NewDecoder creates a new instance of Decoder.