diff --git a/README.md b/README.md
index 0e9a982..d83d255 100644
--- a/README.md
+++ b/README.md
@@ -58,9 +58,13 @@ Documentation can be found at [Godoc](https://godoc.org/github.com/cosiner/flag)
 # Example
 ## Flags
 ```Go
-package flag
+package main
 
-import "fmt"
+import (
+	"fmt"
+
+	flag "github.com/cosiner/flag"
+)
 
 type Tar struct {
 	GZ          bool     `names:"-z, --gz" usage:"gzip format"`
@@ -73,7 +77,7 @@ type Tar struct {
 	SourceFiles []string `args:"true"`
 }
 
-func (t *Tar) Metadata() map[string]Flag {
+func (t *Tar) Metadata() map[string]flag.Flag {
 	const (
 		usage   = "tar is a tool for manipulate tape archives."
 		version = `
@@ -87,7 +91,7 @@ func (t *Tar) Metadata() map[string]Flag {
 		cpio, ar, and shar archives.
 		`
 	)
-	return map[string]Flag{
+	return map[string]flag.Flag{
 		"": {
 			Usage:   usage,
 			Version: version,
@@ -99,22 +103,21 @@ func (t *Tar) Metadata() map[string]Flag {
 	}
 }
 
-func ExampleFlagSet_ParseStruct() {
+func main() {
 	var tar Tar
 
-	NewFlagSet(Flag{}).ParseStruct(&tar, "tar", "-zcf", "a.tgz", "a.go", "b.go")
+	flag.NewFlagSet(flag.Flag{}).ParseStruct(&tar, os.Args...)
 	fmt.Println(tar.GZ)
 	fmt.Println(tar.Create)
 	fmt.Println(tar.File)
 	fmt.Println(tar.SourceFiles)
 
-	// Output:
+	// Output for `$ go build -o "tar" . && ./tar -zcf a.tgz a.go b.go`:
 	// true
 	// true
 	// a.tgz
 	// [a.go b.go]
 }
-
 ```
 ## Help message
 ```
@@ -146,6 +149,14 @@ Flags:
 
 ## FlagSet
 ```Go
+package main
+
+import (
+	"fmt"
+
+	flag "github.com/cosiner/flag"
+)
+
 
 type GoCmd struct {
 	Build struct {
@@ -160,25 +171,10 @@ type GoCmd struct {
 	Clean struct {
 		Enable bool
 	} `usage:"remove object files"`
-	Doc struct {
-		Enable bool
-	} `usage:"show documentation for package or symbol"`
-	Env struct {
-		Enable bool
-	} `usage:"print Go environment information"`
-	Bug struct {
-		Enable bool
-	} `usage:"start a bug report"`
-	Fix struct {
-		Enable bool
-	} `usage:"run go tool fix on packages"`
-	Fmt struct {
-		Enable bool
-	} `usage:"run gofmt on package sources"`
 }
 
-func (*GoCmd) Metadata() map[string]Flag {
-	return map[string]Flag{
+func (*GoCmd) Metadata() map[string]flag.Flag {
+	return map[string]flag.Flag{
 		"": {
 			Usage:   "Go is a tool for managing Go source code.",
 			Arglist: "command [argument]",
@@ -196,16 +192,31 @@ func (*GoCmd) Metadata() map[string]Flag {
 	}
 }
 
-func TestSubset(t *testing.T) {
+func main() {
 	var g GoCmd
 
-	set := NewFlagSet(Flag{})
-	set.StructFlags(&g)
-	set.Help(false)
-	fmt.Println()
-	build, _ := set.FindSubset("build")
-	build.Help(false)
+	set := flag.NewFlagSet(flag.Flag{})
+	set.ParseStruct(&g, os.Args...)
+
+	if g.Build.Enable {
+		if len(g.Build.Packages) == 0 {
+			fmt.Fprintln(os.Stderr, "Error: you should at least specify one package")
+			fmt.Println("")
+			build, _ := set.FindSubset("build")
+			build.Help(false) // display usage information for the "go build" command only
+		} else {
+			fmt.Println("Going to build with the following parameters:")
+			fmt.Println(g.Build)
+		}
+	} else if g.Clean.Enable {
+		fmt.Println("Going to clean with the following parameters:")
+		fmt.Println(g.Clean)
+	} else {
+		set.Help(false) // display usage information, with list of supported commands
+	}
 }
+
+// Test with `$ go build -o "go" . && ./go --help`
 ```
 ##Help Message
 ```