## Hello
### This is a test message
Ligisnfmkdfn

<h2 id="helo">Hello</h2>
<h3 id="this-is-a-test-message">This is a test message</h3>
<p>Ligisnfmkdfn</p>

<section id="helo">
   <h2>Hello</h2>
   <section id="this-is-a-test-message">
      <h3>This is a test message</h3>
      <p>Ligisnfmkdfn</p>
   </section>
</section>

package main
import (
	"fmt"
	"io"
	"regexp"
	"strings"
	"github.com/gomarkdown/markdown"
	"github.com/gomarkdown/markdown/ast"
	"github.com/gomarkdown/markdown/html"
)
// levels tracks how deep we are in a heading "structure"
var levels []int
func hasLevels() bool {
	return len(levels) > 0
}
func lastLevel() int {
	if hasLevels() {
		return levels[len(levels)-1]
	}
	return 0
}
func popLevel() int {
	level := lastLevel()
	levels = levels[:len(levels)-1]
	return level
}
func pushLevel(x int) {
	levels = append(levels, x)
}
var reID = regexp.MustCompile(`\s+`)
// renderSections catches an ast.Heading node, and wraps the node
// and its "children" nodes in <section>...</section> tags; there's no
// real hierarchy in Markdown, so we make one up by saying things like:
// - H2 is a child of H1, and so forth from 1 → 2 → 3 ... → N
// - an H1 is a sibling of another H1
func renderSections(w io.Writer, node ast.Node, entering bool) (ast.WalkStatus, bool) {
	openSection := func(level int, id string) {
		w.Write([]byte(fmt.Sprintf("<section id=\"%s\">\n", id)))
		pushLevel(level)
	}
	closeSection := func() {
		w.Write([]byte("</section>\n"))
		popLevel()
	}
	if _, ok := node.(*ast.Heading); ok {
		level := node.(*ast.Heading).Level
		if entering {
			// close heading-sections deeper than this level; we've "come up" some number of levels
			for lastLevel() > level {
				closeSection()
			}
			txtNode := node.GetChildren()[0]
			if _, ok := txtNode.(*ast.Text); !ok {
				panic(fmt.Errorf("expected txtNode to be *ast.Text; got %T", txtNode))
			}
			headTxt := string(txtNode.AsLeaf().Literal)
			id := strings.ToLower(reID.ReplaceAllString(headTxt, "-"))
			openSection(level, id)
		}
	}
	// at end of document
	if _, ok := node.(*ast.Document); ok {
		if !entering {
			for hasLevels() {
				closeSection()
			}
		}
	}
	// continue as normal
	return ast.GoToNext, false
}
func main() {
	lines := []string{
		"## Hello",
		"### This is a test message",
		"Ligisnfmkdfn",
	}
	md := strings.Join(lines, "\n")
	opts := html.RendererOptions{
		Flags:          html.CommonFlags,
		RenderNodeHook: renderSections,
	}
	renderer := html.NewRenderer(opts)
	html := markdown.ToHTML([]byte(md), nil, renderer)
	fmt.Println(string(html))
}

<section id="hello">
  <h2>Hello</h2>
  <section id="this-is-a-test-message">
    <h3>This is a test message</h3>
    <p>Ligisnfmkdfn</p>
  </section>
</section>

lines := []string{
    "# H1α",
    "## H2A",
    "## H2B",
    "## H2C",
    "### H31",
    "#### H4I",
    "## H2D",
    "# H1β",
    "## H2E",
}

<section id="h1α">
  <h1>H1α</h1>
  <section id="h2a">
    <h2>H2A</h2>
  </section>
  <section id="h2b">
    <h2>H2B</h2>
  </section>
  <section id="h2c">
    <h2>H2C</h2>
    <section id="h31">
      <h3>H31</h3>
      <section id="h4i">
        <h4>H4I</h4>
      </section>
    </section>
  </section>
  <section id="h2d">
    <h2>H2D</h2>
  </section>
</section>
<section id="h1β">
  <h1>H1β</h1>
  <section id="h2e">
    <h2>H2E</h2>
  </section>
</section>