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// Copyright © 2016 Alan A. A. Donovan & Brian W. Kernighan.
// License: https://creativecommons.org/licenses/by-nc-sa/4.0/

// See page 123.

// Outline prints the outline of an HTML document tree.
package main

import (
    "fmt"
    "os"

    "golang.org/x/net/html"
)

//!+
func main() {
    doc, err := html.Parse(os.Stdin)
    if err != nil {
        fmt.Fprintf(os.Stderr, "outline: %v\n", err)
        os.Exit(1)
    }
    outline(nil, doc)
}

func outline(stack []string, n *html.Node) {
    if n.Type == html.ElementNode {
        stack = append(stack, n.Data) // push tag
        fmt.Println(stack)
    }
    for c := n.FirstChild; c != nil; c = c.NextSibling {
        outline(stack, c)
    }
}

//!-