@@ -0,0 +1,187 @@
+package htmlformat
+
+import (
+	"fmt"
+	"io"
+	"strings"
+
+	"golang.org/x/net/html"
+	"golang.org/x/net/html/atom"
+)
+
+// Document formats a HTML document.
+func Document(w io.Writer, r io.Reader) (err error) {
+	node, err := html.Parse(r)
+	if err != nil {
+		return err
+	}
+	return Nodes(w, []*html.Node{node})
+}
+
+// Fragment formats a fragment of a HTML document.
+func Fragment(w io.Writer, r io.Reader) (err error) {
+	context := &html.Node{
+		Type: html.ElementNode,
+	}
+	nodes, err := html.ParseFragment(r, context)
+	if err != nil {
+		return err
+	}
+	return Nodes(w, nodes)
+}
+
+// Nodes formats a slice of HTML nodes.
+func Nodes(w io.Writer, nodes []*html.Node) (err error) {
+	for _, node := range nodes {
+		if err = printNode(w, node, 0); err != nil {
+			return
+		}
+	}
+	return
+}
+
+// The <pre> tag indicates that the text within it should always be formatted
+// as is. See https://github.com/ericchiang/pup/issues/33
+func printPre(w io.Writer, n *html.Node) (err error) {
+	switch n.Type {
+	case html.TextNode:
+		s := n.Data
+		if _, err = fmt.Fprint(w, s); err != nil {
+			return
+		}
+		for c := n.FirstChild; c != nil; c = c.NextSibling {
+			if err = printPre(w, c); err != nil {
+				return
+			}
+		}
+	case html.ElementNode:
+		if _, err = fmt.Fprintf(w, "<%s", n.Data); err != nil {
+			return
+		}
+		for _, a := range n.Attr {
+			val := a.Val
+			if _, err = fmt.Fprintf(w, ` %s="%s"`, a.Key, val); err != nil {
+				return
+			}
+		}
+		if _, err = fmt.Fprint(w, ">"); err != nil {
+			return
+		}
+		if !isVoidElement(n) {
+			for c := n.FirstChild; c != nil; c = c.NextSibling {
+				if err = printPre(w, c); err != nil {
+					return
+				}
+			}
+			if _, err = fmt.Fprintf(w, "</%s>", n.Data); err != nil {
+				return
+			}
+		}
+	case html.CommentNode:
+		data := n.Data
+		if _, err = fmt.Fprintf(w, "<!--%s-->\n", data); err != nil {
+			return
+		}
+		for c := n.FirstChild; c != nil; c = c.NextSibling {
+			if err = printPre(w, c); err != nil {
+				return
+			}
+		}
+	case html.DoctypeNode, html.DocumentNode:
+		for c := n.FirstChild; c != nil; c = c.NextSibling {
+			if err = printPre(w, c); err != nil {
+				return
+			}
+		}
+	}
+	return
+}
+
+// Is this node a tag with no end tag such as <meta> or <br>?
+// http://www.w3.org/TR/html-markup/syntax.html#syntax-elements
+func isVoidElement(n *html.Node) bool {
+	switch n.DataAtom {
+	case atom.Area, atom.Base, atom.Br, atom.Col, atom.Command, atom.Embed,
+		atom.Hr, atom.Img, atom.Input, atom.Keygen, atom.Link,
+		atom.Meta, atom.Param, atom.Source, atom.Track, atom.Wbr:
+		return true
+	}
+	return false
+}
+
+func printNode(w io.Writer, n *html.Node, level int) (err error) {
+	switch n.Type {
+	case html.TextNode:
+		s := n.Data
+		s = strings.TrimSpace(s)
+		if s != "" {
+			if err = printIndent(w, level); err != nil {
+				return
+			}
+			if _, err = fmt.Fprintln(w, s); err != nil {
+				return
+			}
+		}
+	case html.ElementNode:
+		if err = printIndent(w, level); err != nil {
+			return
+		}
+		if _, err = fmt.Fprintf(w, "<%s", n.Data); err != nil {
+			return
+		}
+		for _, a := range n.Attr {
+			if _, err = fmt.Fprintf(w, ` %s="%s"`, a.Key, a.Val); err != nil {
+				return
+			}
+		}
+		if _, err = fmt.Fprintln(w, ">"); err != nil {
+			return
+		}
+		if !isVoidElement(n) {
+			if err = printChildren(w, n, level+1); err != nil {
+				return
+			}
+			if err = printIndent(w, level); err != nil {
+				return
+			}
+			if _, err = fmt.Fprintf(w, "</%s>\n", n.Data); err != nil {
+				return
+			}
+		}
+	case html.CommentNode:
+		if err = printIndent(w, level); err != nil {
+			return
+		}
+		if _, err = fmt.Fprintf(w, "<!--%s-->\n", n.Data); err != nil {
+			return
+		}
+		if err = printChildren(w, n, level); err != nil {
+			return
+		}
+	case html.DoctypeNode, html.DocumentNode:
+		if err = printChildren(w, n, level); err != nil {
+			return
+		}
+	}
+	return
+}
+
+func printChildren(w io.Writer, n *html.Node, level int) (err error) {
+	child := n.FirstChild
+	for child != nil {
+		if err = printNode(w, child, level); err != nil {
+			return
+		}
+		child = child.NextSibling
+	}
+	return
+}
+
+func printIndent(w io.Writer, level int) (err error) {
+	for ; level > 0; level-- {
+		if _, err = fmt.Fprint(w, " "); err != nil {
+			return
+		}
+	}
+	return
+}