code: func (e *Encoder) Responder(r *http.Request) Responder {
  	accept := r.Header.Get("Accept")
  	infoList := parseAcceptHeader(accept)
  
  	for _, info := range infoList {
  		for encoding, i := range e.encodings {
  			if i.equals(info) {
  				return encoding
  			}
  		}
  	}
  
  	return e.Parser(r).(Responder)
  }
docs: // Responder returns a responder based on the mime, if none can be matched the
  // default is returned