"text/template" issue for embed string struct

StringTrap.go

package main

import (
	"log"
	"os"
	"strings"
	"text/template"
)

type myStr string
type myStruct struct {
	string
}

func main() {
	const (
		master  = `Names:{{block "list" .}}{{"\n"}}{{range .}}{{printf "- %t\n" . }}{{end}}{{end}}`
		overlay = `{{define "list"}} {{join . ", "}}{{end}} `
	)
	var (
		funcs     = template.FuncMap{"join": strings.Join}
		guardians = []interface{}{myStruct{"123"}, "Gamora", "Groot", "Nebula", "Rocket", "Star-Lord"}
	)
	masterTmpl, err := template.New("master").Funcs(funcs).Parse(master)
	if err != nil {
		log.Fatal(err)
	}
	overlayTmpl, err := template.Must(masterTmpl.Clone()).Parse(overlay)
	if err != nil {
		log.Fatal(err)
	}
	if err := masterTmpl.Execute(os.Stdout, guardians); err != nil {
		log.Fatal(err)
	}
	if err := overlayTmpl.Execute(os.Stdout, guardians); err != nil {
		log.Fatal(err)
	}
}

https://play.golang.org/p/XXaKg5I7npI

A can fmt.Sprintf("%s", A) as a string do not mean A is the type of string which A might be

type MyStruct struct{
    string
}

A := MyStruct{"text"}