[question] "+" symbol about schema HOT 6 OPEN

package main

import (
	"fmt"
	"log"
	"net/http"
)

func main() {

	http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
		fmt.Println(r.URL.Query().Get("phone"))
	})

	log.Fatal(http.ListenAndServe(":9090", nil))

}

import (
	"fmt"
	"net/http"
	"net/http/httptest"
	"reflect"
	"strings"

	"github.com/gorilla/schema"
)

type RequestParams struct {
	Name  string
	Phone string
}

func main() {
        name := "gorilla-schema"
        phone := "+123456789"
        
	r := httptest.NewRequest(http.MethodGet, "http://example.com", nil)
	q := r.URL.Query()
	q.Add("name", name)
	q.Add("phone", phone)
	r.URL.RawQuery = q.Encode()

	var query RequestParams
	decoder := schema.NewDecoder()
	decoder.RegisterConverter([]string{}, func(input string) reflect.Value {
		return reflect.ValueOf(strings.Split(input, ","))
	})
	if err := decoder.Decode(&query, r.URL.Query()); err != nil {
		fmt.Println(err)
	}
	fmt.Printf("name: expected %s, got %s, they match: %t\n", name, query.Name, name==query.Name)
	fmt.Printf("phone: expected %s, got %s, they match: %t\n", phone, query.Phone, phone==query.Phone)