blockActionDemo.go

package main

import (
	"fmt"
	"html/template"
	"os"
)

var templateDemo = `
{{ define "a" }} 
Template A includes Template B
{{ block "b" .}} Template B {{ end }}
Template A ends
{{ end }}
`

func main() {
	var err error

	t := template.New("templateActionDemo")

	t, err = t.Parse(templateDemo)

	if err != nil {
		fmt.Println("parsing failed: %s", err)
	}
	err = t.ExecuteTemplate(os.Stdout, "a", nil)
	if err != nil {
		fmt.Println("execution failed: %s", err)
	}

}

output

Template A includes Template B                                                                                                                                              
 Template B                                                                                                                                                                 
Template A ends