vendor HEAD main

1 files changed, 1272 insertions, 0 deletions

diff --git a/vendor/golang.org/x/net/html/token.go b/vendor/golang.org/x/net/html/token.go
new file mode 100644
index 0000000..3c57880
--- /dev/null
+++ b/vendor/golang.org/x/net/html/token.go
@@ -0,0 +1,1272 @@
+// Copyright 2010 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package html
+
+import (
+	"bytes"
+	"errors"
+	"io"
+	"strconv"
+	"strings"
+
+	"golang.org/x/net/html/atom"
+)
+
+// A TokenType is the type of a Token.
+type TokenType uint32
+
+const (
+	// ErrorToken means that an error occurred during tokenization.
+	ErrorToken TokenType = iota
+	// TextToken means a text node.
+	TextToken
+	// A StartTagToken looks like <a>.
+	StartTagToken
+	// An EndTagToken looks like </a>.
+	EndTagToken
+	// A SelfClosingTagToken tag looks like <br/>.
+	SelfClosingTagToken
+	// A CommentToken looks like <!--x-->.
+	CommentToken
+	// A DoctypeToken looks like <!DOCTYPE x>
+	DoctypeToken
+)
+
+// ErrBufferExceeded means that the buffering limit was exceeded.
+var ErrBufferExceeded = errors.New("max buffer exceeded")
+
+// String returns a string representation of the TokenType.
+func (t TokenType) String() string {
+	switch t {
+	case ErrorToken:
+		return "Error"
+	case TextToken:
+		return "Text"
+	case StartTagToken:
+		return "StartTag"
+	case EndTagToken:
+		return "EndTag"
+	case SelfClosingTagToken:
+		return "SelfClosingTag"
+	case CommentToken:
+		return "Comment"
+	case DoctypeToken:
+		return "Doctype"
+	}
+	return "Invalid(" + strconv.Itoa(int(t)) + ")"
+}
+
+// An Attribute is an attribute namespace-key-value triple. Namespace is
+// non-empty for foreign attributes like xlink, Key is alphabetic (and hence
+// does not contain escapable characters like '&', '<' or '>'), and Val is
+// unescaped (it looks like "a<b" rather than "a&lt;b").
+//
+// Namespace is only used by the parser, not the tokenizer.
+type Attribute struct {
+	Namespace, Key, Val string
+}
+
+// A Token consists of a TokenType and some Data (tag name for start and end
+// tags, content for text, comments and doctypes). A tag Token may also contain
+// a slice of Attributes. Data is unescaped for all Tokens (it looks like "a<b"
+// rather than "a&lt;b"). For tag Tokens, DataAtom is the atom for Data, or
+// zero if Data is not a known tag name.
+type Token struct {
+	Type     TokenType
+	DataAtom atom.Atom
+	Data     string
+	Attr     []Attribute
+}
+
+// tagString returns a string representation of a tag Token's Data and Attr.
+func (t Token) tagString() string {
+	if len(t.Attr) == 0 {
+		return t.Data
+	}
+	buf := bytes.NewBufferString(t.Data)
+	for _, a := range t.Attr {
+		buf.WriteByte(' ')
+		buf.WriteString(a.Key)
+		buf.WriteString(`="`)
+		escape(buf, a.Val)
+		buf.WriteByte('"')
+	}
+	return buf.String()
+}
+
+// String returns a string representation of the Token.
+func (t Token) String() string {
+	switch t.Type {
+	case ErrorToken:
+		return ""
+	case TextToken:
+		return EscapeString(t.Data)
+	case StartTagToken:
+		return "<" + t.tagString() + ">"
+	case EndTagToken:
+		return "</" + t.tagString() + ">"
+	case SelfClosingTagToken:
+		return "<" + t.tagString() + "/>"
+	case CommentToken:
+		return "<!--" + escapeCommentString(t.Data) + "-->"
+	case DoctypeToken:
+		return "<!DOCTYPE " + EscapeString(t.Data) + ">"
+	}
+	return "Invalid(" + strconv.Itoa(int(t.Type)) + ")"
+}
+
+// span is a range of bytes in a Tokenizer's buffer. The start is inclusive,
+// the end is exclusive.
+type span struct {
+	start, end int
+}
+
+// A Tokenizer returns a stream of HTML Tokens.
+type Tokenizer struct {
+	// r is the source of the HTML text.
+	r io.Reader
+	// tt is the TokenType of the current token.
+	tt TokenType
+	// err is the first error encountered during tokenization. It is possible
+	// for tt != Error && err != nil to hold: this means that Next returned a
+	// valid token but the subsequent Next call will return an error token.
+	// For example, if the HTML text input was just "plain", then the first
+	// Next call would set z.err to io.EOF but return a TextToken, and all
+	// subsequent Next calls would return an ErrorToken.
+	// err is never reset. Once it becomes non-nil, it stays non-nil.
+	err error
+	// readErr is the error returned by the io.Reader r. It is separate from
+	// err because it is valid for an io.Reader to return (n int, err1 error)
+	// such that n > 0 && err1 != nil, and callers should always process the
+	// n > 0 bytes before considering the error err1.
+	readErr error
+	// buf[raw.start:raw.end] holds the raw bytes of the current token.
+	// buf[raw.end:] is buffered input that will yield future tokens.
+	raw span
+	buf []byte
+	// maxBuf limits the data buffered in buf. A value of 0 means unlimited.
+	maxBuf int
+	// buf[data.start:data.end] holds the raw bytes of the current token's data:
+	// a text token's text, a tag token's tag name, etc.
+	data span
+	// pendingAttr is the attribute key and value currently being tokenized.
+	// When complete, pendingAttr is pushed onto attr. nAttrReturned is
+	// incremented on each call to TagAttr.
+	pendingAttr   [2]span
+	attr          [][2]span
+	nAttrReturned int
+	// rawTag is the "script" in "</script>" that closes the next token. If
+	// non-empty, the subsequent call to Next will return a raw or RCDATA text
+	// token: one that treats "<p>" as text instead of an element.
+	// rawTag's contents are lower-cased.
+	rawTag string
+	// textIsRaw is whether the current text token's data is not escaped.
+	textIsRaw bool
+	// convertNUL is whether NUL bytes in the current token's data should
+	// be converted into \ufffd replacement characters.
+	convertNUL bool
+	// allowCDATA is whether CDATA sections are allowed in the current context.
+	allowCDATA bool
+}
+
+// AllowCDATA sets whether or not the tokenizer recognizes <![CDATA[foo]]> as
+// the text "foo". The default value is false, which means to recognize it as
+// a bogus comment "<!-- [CDATA[foo]] -->" instead.
+//
+// Strictly speaking, an HTML5 compliant tokenizer should allow CDATA if and
+// only if tokenizing foreign content, such as MathML and SVG. However,
+// tracking foreign-contentness is difficult to do purely in the tokenizer,
+// as opposed to the parser, due to HTML integration points: an <svg> element
+// can contain a <foreignObject> that is foreign-to-SVG but not foreign-to-
+// HTML. For strict compliance with the HTML5 tokenization algorithm, it is the
+// responsibility of the user of a tokenizer to call AllowCDATA as appropriate.
+// In practice, if using the tokenizer without caring whether MathML or SVG
+// CDATA is text or comments, such as tokenizing HTML to find all the anchor
+// text, it is acceptable to ignore this responsibility.
+func (z *Tokenizer) AllowCDATA(allowCDATA bool) {
+	z.allowCDATA = allowCDATA
+}
+
+// NextIsNotRawText instructs the tokenizer that the next token should not be
+// considered as 'raw text'. Some elements, such as script and title elements,
+// normally require the next token after the opening tag to be 'raw text' that
+// has no child elements. For example, tokenizing "<title>a<b>c</b>d</title>"
+// yields a start tag token for "<title>", a text token for "a<b>c</b>d", and
+// an end tag token for "</title>". There are no distinct start tag or end tag
+// tokens for the "<b>" and "</b>".
+//
+// This tokenizer implementation will generally look for raw text at the right
+// times. Strictly speaking, an HTML5 compliant tokenizer should not look for
+// raw text if in foreign content: <title> generally needs raw text, but a
+// <title> inside an <svg> does not. Another example is that a <textarea>
+// generally needs raw text, but a <textarea> is not allowed as an immediate
+// child of a <select>; in normal parsing, a <textarea> implies </select>, but
+// one cannot close the implicit element when parsing a <select>'s InnerHTML.
+// Similarly to AllowCDATA, tracking the correct moment to override raw-text-
+// ness is difficult to do purely in the tokenizer, as opposed to the parser.
+// For strict compliance with the HTML5 tokenization algorithm, it is the
+// responsibility of the user of a tokenizer to call NextIsNotRawText as
+// appropriate. In practice, like AllowCDATA, it is acceptable to ignore this
+// responsibility for basic usage.
+//
+// Note that this 'raw text' concept is different from the one offered by the
+// Tokenizer.Raw method.
+func (z *Tokenizer) NextIsNotRawText() {
+	z.rawTag = ""
+}
+
+// Err returns the error associated with the most recent ErrorToken token.
+// This is typically io.EOF, meaning the end of tokenization.
+func (z *Tokenizer) Err() error {
+	if z.tt != ErrorToken {
+		return nil
+	}
+	return z.err
+}
+
+// readByte returns the next byte from the input stream, doing a buffered read
+// from z.r into z.buf if necessary. z.buf[z.raw.start:z.raw.end] remains a contiguous byte
+// slice that holds all the bytes read so far for the current token.
+// It sets z.err if the underlying reader returns an error.
+// Pre-condition: z.err == nil.
+func (z *Tokenizer) readByte() byte {
+	if z.raw.end >= len(z.buf) {
+		// Our buffer is exhausted and we have to read from z.r. Check if the
+		// previous read resulted in an error.
+		if z.readErr != nil {
+			z.err = z.readErr
+			return 0
+		}
+		// We copy z.buf[z.raw.start:z.raw.end] to the beginning of z.buf. If the length
+		// z.raw.end - z.raw.start is more than half the capacity of z.buf, then we
+		// allocate a new buffer before the copy.
+		c := cap(z.buf)
+		d := z.raw.end - z.raw.start
+		var buf1 []byte
+		if 2*d > c {
+			buf1 = make([]byte, d, 2*c)
+		} else {
+			buf1 = z.buf[:d]
+		}
+		copy(buf1, z.buf[z.raw.start:z.raw.end])
+		if x := z.raw.start; x != 0 {
+			// Adjust the data/attr spans to refer to the same contents after the copy.
+			z.data.start -= x
+			z.data.end -= x
+			z.pendingAttr[0].start -= x
+			z.pendingAttr[0].end -= x
+			z.pendingAttr[1].start -= x
+			z.pendingAttr[1].end -= x
+			for i := range z.attr {
+				z.attr[i][0].start -= x
+				z.attr[i][0].end -= x
+				z.attr[i][1].start -= x
+				z.attr[i][1].end -= x
+			}
+		}
+		z.raw.start, z.raw.end, z.buf = 0, d, buf1[:d]
+		// Now that we have copied the live bytes to the start of the buffer,
+		// we read from z.r into the remainder.
+		var n int
+		n, z.readErr = readAtLeastOneByte(z.r, buf1[d:cap(buf1)])
+		if n == 0 {
+			z.err = z.readErr
+			return 0
+		}
+		z.buf = buf1[:d+n]
+	}
+	x := z.buf[z.raw.end]
+	z.raw.end++
+	if z.maxBuf > 0 && z.raw.end-z.raw.start >= z.maxBuf {
+		z.err = ErrBufferExceeded
+		return 0
+	}
+	return x
+}
+
+// Buffered returns a slice containing data buffered but not yet tokenized.
+func (z *Tokenizer) Buffered() []byte {
+	return z.buf[z.raw.end:]
+}
+
+// readAtLeastOneByte wraps an io.Reader so that reading cannot return (0, nil).
+// It returns io.ErrNoProgress if the underlying r.Read method returns (0, nil)
+// too many times in succession.
+func readAtLeastOneByte(r io.Reader, b []byte) (int, error) {
+	for i := 0; i < 100; i++ {
+		if n, err := r.Read(b); n != 0 || err != nil {
+			return n, err
+		}
+	}
+	return 0, io.ErrNoProgress
+}
+
+// skipWhiteSpace skips past any white space.
+func (z *Tokenizer) skipWhiteSpace() {
+	if z.err != nil {
+		return
+	}
+	for {
+		c := z.readByte()
+		if z.err != nil {
+			return
+		}
+		switch c {
+		case ' ', '\n', '\r', '\t', '\f':
+			// No-op.
+		default:
+			z.raw.end--
+			return
+		}
+	}
+}
+
+// readRawOrRCDATA reads until the next "</foo>", where "foo" is z.rawTag and
+// is typically something like "script" or "textarea".
+func (z *Tokenizer) readRawOrRCDATA() {
+	if z.rawTag == "script" {
+		z.readScript()
+		z.textIsRaw = true
+		z.rawTag = ""
+		return
+	}
+loop:
+	for {
+		c := z.readByte()
+		if z.err != nil {
+			break loop
+		}
+		if c != '<' {
+			continue loop
+		}
+		c = z.readByte()
+		if z.err != nil {
+			break loop
+		}
+		if c != '/' {
+			z.raw.end--
+			continue loop
+		}
+		if z.readRawEndTag() || z.err != nil {
+			break loop
+		}
+	}
+	z.data.end = z.raw.end
+	// A textarea's or title's RCDATA can contain escaped entities.
+	z.textIsRaw = z.rawTag != "textarea" && z.rawTag != "title"
+	z.rawTag = ""
+}
+
+// readRawEndTag attempts to read a tag like "</foo>", where "foo" is z.rawTag.
+// If it succeeds, it backs up the input position to reconsume the tag and
+// returns true. Otherwise it returns false. The opening "</" has already been
+// consumed.
+func (z *Tokenizer) readRawEndTag() bool {
+	for i := 0; i < len(z.rawTag); i++ {
+		c := z.readByte()
+		if z.err != nil {
+			return false
+		}
+		if c != z.rawTag[i] && c != z.rawTag[i]-('a'-'A') {
+			z.raw.end--
+			return false
+		}
+	}
+	c := z.readByte()
+	if z.err != nil {
+		return false
+	}
+	switch c {
+	case ' ', '\n', '\r', '\t', '\f', '/', '>':
+		// The 3 is 2 for the leading "</" plus 1 for the trailing character c.
+		z.raw.end -= 3 + len(z.rawTag)
+		return true
+	}
+	z.raw.end--
+	return false
+}
+
+// readScript reads until the next </script> tag, following the byzantine
+// rules for escaping/hiding the closing tag.
+func (z *Tokenizer) readScript() {
+	defer func() {
+		z.data.end = z.raw.end
+	}()
+	var c byte
+
+scriptData:
+	c = z.readByte()
+	if z.err != nil {
+		return
+	}
+	if c == '<' {
+		goto scriptDataLessThanSign
+	}
+	goto scriptData
+
+scriptDataLessThanSign:
+	c = z.readByte()
+	if z.err != nil {
+		return
+	}
+	switch c {
+	case '/':
+		goto scriptDataEndTagOpen
+	case '!':
+		goto scriptDataEscapeStart
+	}
+	z.raw.end--
+	goto scriptData
+
+scriptDataEndTagOpen:
+	if z.readRawEndTag() || z.err != nil {
+		return
+	}
+	goto scriptData
+
+scriptDataEscapeStart:
+	c = z.readByte()
+	if z.err != nil {
+		return
+	}
+	if c == '-' {
+		goto scriptDataEscapeStartDash
+	}
+	z.raw.end--
+	goto scriptData
+
+scriptDataEscapeStartDash:
+	c = z.readByte()
+	if z.err != nil {
+		return
+	}
+	if c == '-' {
+		goto scriptDataEscapedDashDash
+	}
+	z.raw.end--
+	goto scriptData
+
+scriptDataEscaped:
+	c = z.readByte()
+	if z.err != nil {
+		return
+	}
+	switch c {
+	case '-':
+		goto scriptDataEscapedDash
+	case '<':
+		goto scriptDataEscapedLessThanSign
+	}
+	goto scriptDataEscaped
+
+scriptDataEscapedDash:
+	c = z.readByte()
+	if z.err != nil {
+		return
+	}
+	switch c {
+	case '-':
+		goto scriptDataEscapedDashDash
+	case '<':
+		goto scriptDataEscapedLessThanSign
+	}
+	goto scriptDataEscaped
+
+scriptDataEscapedDashDash:
+	c = z.readByte()
+	if z.err != nil {
+		return
+	}
+	switch c {
+	case '-':
+		goto scriptDataEscapedDashDash
+	case '<':
+		goto scriptDataEscapedLessThanSign
+	case '>':
+		goto scriptData
+	}
+	goto scriptDataEscaped
+
+scriptDataEscapedLessThanSign:
+	c = z.readByte()
+	if z.err != nil {
+		return
+	}
+	if c == '/' {
+		goto scriptDataEscapedEndTagOpen
+	}
+	if 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' {
+		goto scriptDataDoubleEscapeStart
+	}
+	z.raw.end--
+	goto scriptData
+
+scriptDataEscapedEndTagOpen:
+	if z.readRawEndTag() || z.err != nil {
+		return
+	}
+	goto scriptDataEscaped
+
+scriptDataDoubleEscapeStart:
+	z.raw.end--
+	for i := 0; i < len("script"); i++ {
+		c = z.readByte()
+		if z.err != nil {
+			return
+		}
+		if c != "script"[i] && c != "SCRIPT"[i] {
+			z.raw.end--
+			goto scriptDataEscaped
+		}
+	}
+	c = z.readByte()
+	if z.err != nil {
+		return
+	}
+	switch c {
+	case ' ', '\n', '\r', '\t', '\f', '/', '>':
+		goto scriptDataDoubleEscaped
+	}
+	z.raw.end--
+	goto scriptDataEscaped
+
+scriptDataDoubleEscaped:
+	c = z.readByte()
+	if z.err != nil {
+		return
+	}
+	switch c {
+	case '-':
+		goto scriptDataDoubleEscapedDash
+	case '<':
+		goto scriptDataDoubleEscapedLessThanSign
+	}
+	goto scriptDataDoubleEscaped
+
+scriptDataDoubleEscapedDash:
+	c = z.readByte()
+	if z.err != nil {
+		return
+	}
+	switch c {
+	case '-':
+		goto scriptDataDoubleEscapedDashDash
+	case '<':
+		goto scriptDataDoubleEscapedLessThanSign
+	}
+	goto scriptDataDoubleEscaped
+
+scriptDataDoubleEscapedDashDash:
+	c = z.readByte()
+	if z.err != nil {
+		return
+	}
+	switch c {
+	case '-':
+		goto scriptDataDoubleEscapedDashDash
+	case '<':
+		goto scriptDataDoubleEscapedLessThanSign
+	case '>':
+		goto scriptData
+	}
+	goto scriptDataDoubleEscaped
+
+scriptDataDoubleEscapedLessThanSign:
+	c = z.readByte()
+	if z.err != nil {
+		return
+	}
+	if c == '/' {
+		goto scriptDataDoubleEscapeEnd
+	}
+	z.raw.end--
+	goto scriptDataDoubleEscaped
+
+scriptDataDoubleEscapeEnd:
+	if z.readRawEndTag() {
+		z.raw.end += len("</script>")
+		goto scriptDataEscaped
+	}
+	if z.err != nil {
+		return
+	}
+	goto scriptDataDoubleEscaped
+}
+
+// readComment reads the next comment token starting with "<!--". The opening
+// "<!--" has already been consumed.
+func (z *Tokenizer) readComment() {
+	// When modifying this function, consider manually increasing the
+	// maxSuffixLen constant in func TestComments, from 6 to e.g. 9 or more.
+	// That increase should only be temporary, not committed, as it
+	// exponentially affects the test running time.
+
+	z.data.start = z.raw.end
+	defer func() {
+		if z.data.end < z.data.start {
+			// It's a comment with no data, like <!-->.
+			z.data.end = z.data.start
+		}
+	}()
+
+	var dashCount int
+	beginning := true
+	for {
+		c := z.readByte()
+		if z.err != nil {
+			z.data.end = z.calculateAbruptCommentDataEnd()
+			return
+		}
+		switch c {
+		case '-':
+			dashCount++
+			continue
+		case '>':
+			if dashCount >= 2 || beginning {
+				z.data.end = z.raw.end - len("-->")
+				return
+			}
+		case '!':
+			if dashCount >= 2 {
+				c = z.readByte()
+				if z.err != nil {
+					z.data.end = z.calculateAbruptCommentDataEnd()
+					return
+				} else if c == '>' {
+					z.data.end = z.raw.end - len("--!>")
+					return
+				} else if c == '-' {
+					dashCount = 1
+					beginning = false
+					continue
+				}
+			}
+		}
+		dashCount = 0
+		beginning = false
+	}
+}
+
+func (z *Tokenizer) calculateAbruptCommentDataEnd() int {
+	raw := z.Raw()
+	const prefixLen = len("<!--")
+	if len(raw) >= prefixLen {
+		raw = raw[prefixLen:]
+		if hasSuffix(raw, "--!") {
+			return z.raw.end - 3
+		} else if hasSuffix(raw, "--") {
+			return z.raw.end - 2
+		} else if hasSuffix(raw, "-") {
+			return z.raw.end - 1
+		}
+	}
+	return z.raw.end
+}
+
+func hasSuffix(b []byte, suffix string) bool {
+	if len(b) < len(suffix) {
+		return false
+	}
+	b = b[len(b)-len(suffix):]
+	for i := range b {
+		if b[i] != suffix[i] {
+			return false
+		}
+	}
+	return true
+}
+
+// readUntilCloseAngle reads until the next ">".
+func (z *Tokenizer) readUntilCloseAngle() {
+	z.data.start = z.raw.end
+	for {
+		c := z.readByte()
+		if z.err != nil {
+			z.data.end = z.raw.end
+			return
+		}
+		if c == '>' {
+			z.data.end = z.raw.end - len(">")
+			return
+		}
+	}
+}
+
+// readMarkupDeclaration reads the next token starting with "<!". It might be
+// a "<!--comment-->", a "<!DOCTYPE foo>", a "<![CDATA[section]]>" or
+// "<!a bogus comment". The opening "<!" has already been consumed.
+func (z *Tokenizer) readMarkupDeclaration() TokenType {
+	z.data.start = z.raw.end
+	var c [2]byte
+	for i := 0; i < 2; i++ {
+		c[i] = z.readByte()
+		if z.err != nil {
+			z.data.end = z.raw.end
+			return CommentToken
+		}
+	}
+	if c[0] == '-' && c[1] == '-' {
+		z.readComment()
+		return CommentToken
+	}
+	z.raw.end -= 2
+	if z.readDoctype() {
+		return DoctypeToken
+	}
+	if z.allowCDATA && z.readCDATA() {
+		z.convertNUL = true
+		return TextToken
+	}
+	// It's a bogus comment.
+	z.readUntilCloseAngle()
+	return CommentToken
+}
+
+// readDoctype attempts to read a doctype declaration and returns true if
+// successful. The opening "<!" has already been consumed.
+func (z *Tokenizer) readDoctype() bool {
+	const s = "DOCTYPE"
+	for i := 0; i < len(s); i++ {
+		c := z.readByte()
+		if z.err != nil {
+			z.data.end = z.raw.end
+			return false
+		}
+		if c != s[i] && c != s[i]+('a'-'A') {
+			// Back up to read the fragment of "DOCTYPE" again.
+			z.raw.end = z.data.start
+			return false
+		}
+	}
+	if z.skipWhiteSpace(); z.err != nil {
+		z.data.start = z.raw.end
+		z.data.end = z.raw.end
+		return true
+	}
+	z.readUntilCloseAngle()
+	return true
+}
+
+// readCDATA attempts to read a CDATA section and returns true if
+// successful. The opening "<!" has already been consumed.
+func (z *Tokenizer) readCDATA() bool {
+	const s = "[CDATA["
+	for i := 0; i < len(s); i++ {
+		c := z.readByte()
+		if z.err != nil {
+			z.data.end = z.raw.end
+			return false
+		}
+		if c != s[i] {
+			// Back up to read the fragment of "[CDATA[" again.
+			z.raw.end = z.data.start
+			return false
+		}
+	}
+	z.data.start = z.raw.end
+	brackets := 0
+	for {
+		c := z.readByte()
+		if z.err != nil {
+			z.data.end = z.raw.end
+			return true
+		}
+		switch c {
+		case ']':
+			brackets++
+		case '>':
+			if brackets >= 2 {
+				z.data.end = z.raw.end - len("]]>")
+				return true
+			}
+			brackets = 0
+		default:
+			brackets = 0
+		}
+	}
+}
+
+// startTagIn returns whether the start tag in z.buf[z.data.start:z.data.end]
+// case-insensitively matches any element of ss.
+func (z *Tokenizer) startTagIn(ss ...string) bool {
+loop:
+	for _, s := range ss {
+		if z.data.end-z.data.start != len(s) {
+			continue loop
+		}
+		for i := 0; i < len(s); i++ {
+			c := z.buf[z.data.start+i]
+			if 'A' <= c && c <= 'Z' {
+				c += 'a' - 'A'
+			}
+			if c != s[i] {
+				continue loop
+			}
+		}
+		return true
+	}
+	return false
+}
+
+// readStartTag reads the next start tag token. The opening "<a" has already
+// been consumed, where 'a' means anything in [A-Za-z].
+func (z *Tokenizer) readStartTag() TokenType {
+	z.readTag(true)
+	if z.err != nil {
+		return ErrorToken
+	}
+	// Several tags flag the tokenizer's next token as raw.
+	c, raw := z.buf[z.data.start], false
+	if 'A' <= c && c <= 'Z' {
+		c += 'a' - 'A'
+	}
+	switch c {
+	case 'i':
+		raw = z.startTagIn("iframe")
+	case 'n':
+		raw = z.startTagIn("noembed", "noframes", "noscript")
+	case 'p':
+		raw = z.startTagIn("plaintext")
+	case 's':
+		raw = z.startTagIn("script", "style")
+	case 't':
+		raw = z.startTagIn("textarea", "title")
+	case 'x':
+		raw = z.startTagIn("xmp")
+	}
+	if raw {
+		z.rawTag = strings.ToLower(string(z.buf[z.data.start:z.data.end]))
+	}
+	// Look for a self-closing token like "<br/>".
+	if z.err == nil && z.buf[z.raw.end-2] == '/' {
+		return SelfClosingTagToken
+	}
+	return StartTagToken
+}
+
+// readTag reads the next tag token and its attributes. If saveAttr, those
+// attributes are saved in z.attr, otherwise z.attr is set to an empty slice.
+// The opening "<a" or "</a" has already been consumed, where 'a' means anything
+// in [A-Za-z].
+func (z *Tokenizer) readTag(saveAttr bool) {
+	z.attr = z.attr[:0]
+	z.nAttrReturned = 0
+	// Read the tag name and attribute key/value pairs.
+	z.readTagName()
+	if z.skipWhiteSpace(); z.err != nil {
+		return
+	}
+	for {
+		c := z.readByte()
+		if z.err != nil || c == '>' {
+			break
+		}
+		z.raw.end--
+		z.readTagAttrKey()
+		z.readTagAttrVal()
+		// Save pendingAttr if saveAttr and that attribute has a non-empty key.
+		if saveAttr && z.pendingAttr[0].start != z.pendingAttr[0].end {
+			z.attr = append(z.attr, z.pendingAttr)
+		}
+		if z.skipWhiteSpace(); z.err != nil {
+			break
+		}
+	}
+}
+
+// readTagName sets z.data to the "div" in "<div k=v>". The reader (z.raw.end)
+// is positioned such that the first byte of the tag name (the "d" in "<div")
+// has already been consumed.
+func (z *Tokenizer) readTagName() {
+	z.data.start = z.raw.end - 1
+	for {
+		c := z.readByte()
+		if z.err != nil {
+			z.data.end = z.raw.end
+			return
+		}
+		switch c {
+		case ' ', '\n', '\r', '\t', '\f':
+			z.data.end = z.raw.end - 1
+			return
+		case '/', '>':
+			z.raw.end--
+			z.data.end = z.raw.end
+			return
+		}
+	}
+}
+
+// readTagAttrKey sets z.pendingAttr[0] to the "k" in "<div k=v>".
+// Precondition: z.err == nil.
+func (z *Tokenizer) readTagAttrKey() {
+	z.pendingAttr[0].start = z.raw.end
+	for {
+		c := z.readByte()
+		if z.err != nil {
+			z.pendingAttr[0].end = z.raw.end
+			return
+		}
+		switch c {
+		case '=':
+			if z.pendingAttr[0].start+1 == z.raw.end {
+				// WHATWG 13.2.5.32, if we see an equals sign before the attribute name
+				// begins, we treat it as a character in the attribute name and continue.
+				continue
+			}
+			fallthrough
+		case ' ', '\n', '\r', '\t', '\f', '/', '>':
+			// WHATWG 13.2.5.33 Attribute name state
+			// We need to reconsume the char in the after attribute name state to support the / character
+			z.raw.end--
+			z.pendingAttr[0].end = z.raw.end
+			return
+		}
+	}
+}
+
+// readTagAttrVal sets z.pendingAttr[1] to the "v" in "<div k=v>".
+func (z *Tokenizer) readTagAttrVal() {
+	z.pendingAttr[1].start = z.raw.end
+	z.pendingAttr[1].end = z.raw.end
+	if z.skipWhiteSpace(); z.err != nil {
+		return
+	}
+	c := z.readByte()
+	if z.err != nil {
+		return
+	}
+	if c == '/' {
+		// WHATWG 13.2.5.34 After attribute name state
+		// U+002F SOLIDUS (/) - Switch to the self-closing start tag state.
+		return
+	}
+	if c != '=' {
+		z.raw.end--
+		return
+	}
+	if z.skipWhiteSpace(); z.err != nil {
+		return
+	}
+	quote := z.readByte()
+	if z.err != nil {
+		return
+	}
+	switch quote {
+	case '>':
+		z.raw.end--
+		return
+
+	case '\'', '"':
+		z.pendingAttr[1].start = z.raw.end
+		for {
+			c := z.readByte()
+			if z.err != nil {
+				z.pendingAttr[1].end = z.raw.end
+				return
+			}
+			if c == quote {
+				z.pendingAttr[1].end = z.raw.end - 1
+				return
+			}
+		}
+
+	default:
+		z.pendingAttr[1].start = z.raw.end - 1
+		for {
+			c := z.readByte()
+			if z.err != nil {
+				z.pendingAttr[1].end = z.raw.end
+				return
+			}
+			switch c {
+			case ' ', '\n', '\r', '\t', '\f':
+				z.pendingAttr[1].end = z.raw.end - 1
+				return
+			case '>':
+				z.raw.end--
+				z.pendingAttr[1].end = z.raw.end
+				return
+			}
+		}
+	}
+}
+
+// Next scans the next token and returns its type.
+func (z *Tokenizer) Next() TokenType {
+	z.raw.start = z.raw.end
+	z.data.start = z.raw.end
+	z.data.end = z.raw.end
+	if z.err != nil {
+		z.tt = ErrorToken
+		return z.tt
+	}
+	if z.rawTag != "" {
+		if z.rawTag == "plaintext" {
+			// Read everything up to EOF.
+			for z.err == nil {
+				z.readByte()
+			}
+			z.data.end = z.raw.end
+			z.textIsRaw = true
+		} else {
+			z.readRawOrRCDATA()
+		}
+		if z.data.end > z.data.start {
+			z.tt = TextToken
+			z.convertNUL = true
+			return z.tt
+		}
+	}
+	z.textIsRaw = false
+	z.convertNUL = false
+
+loop:
+	for {
+		c := z.readByte()
+		if z.err != nil {
+			break loop
+		}
+		if c != '<' {
+			continue loop
+		}
+
+		// Check if the '<' we have just read is part of a tag, comment
+		// or doctype. If not, it's part of the accumulated text token.
+		c = z.readByte()
+		if z.err != nil {
+			break loop
+		}
+		var tokenType TokenType
+		switch {
+		case 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z':
+			tokenType = StartTagToken
+		case c == '/':
+			tokenType = EndTagToken
+		case c == '!' || c == '?':
+			// We use CommentToken to mean any of "<!--actual comments-->",
+			// "<!DOCTYPE declarations>" and "<?xml processing instructions?>".
+			tokenType = CommentToken
+		default:
+			// Reconsume the current character.
+			z.raw.end--
+			continue
+		}
+
+		// We have a non-text token, but we might have accumulated some text
+		// before that. If so, we return the text first, and return the non-
+		// text token on the subsequent call to Next.
+		if x := z.raw.end - len("<a"); z.raw.start < x {
+			z.raw.end = x
+			z.data.end = x
+			z.tt = TextToken
+			return z.tt
+		}
+		switch tokenType {
+		case StartTagToken:
+			z.tt = z.readStartTag()
+			return z.tt
+		case EndTagToken:
+			c = z.readByte()
+			if z.err != nil {
+				break loop
+			}
+			if c == '>' {
+				// "</>" does not generate a token at all. Generate an empty comment
+				// to allow passthrough clients to pick up the data using Raw.
+				// Reset the tokenizer state and start again.
+				z.tt = CommentToken
+				return z.tt
+			}
+			if 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' {
+				z.readTag(false)
+				if z.err != nil {
+					z.tt = ErrorToken
+				} else {
+					z.tt = EndTagToken
+				}
+				return z.tt
+			}
+			z.raw.end--
+			z.readUntilCloseAngle()
+			z.tt = CommentToken
+			return z.tt
+		case CommentToken:
+			if c == '!' {
+				z.tt = z.readMarkupDeclaration()
+				return z.tt
+			}
+			z.raw.end--
+			z.readUntilCloseAngle()
+			z.tt = CommentToken
+			return z.tt
+		}
+	}
+	if z.raw.start < z.raw.end {
+		z.data.end = z.raw.end
+		z.tt = TextToken
+		return z.tt
+	}
+	z.tt = ErrorToken
+	return z.tt
+}
+
+// Raw returns the unmodified text of the current token. Calling Next, Token,
+// Text, TagName or TagAttr may change the contents of the returned slice.
+//
+// The token stream's raw bytes partition the byte stream (up until an
+// ErrorToken). There are no overlaps or gaps between two consecutive token's
+// raw bytes. One implication is that the byte offset of the current token is
+// the sum of the lengths of all previous tokens' raw bytes.
+func (z *Tokenizer) Raw() []byte {
+	return z.buf[z.raw.start:z.raw.end]
+}
+
+// convertNewlines converts "\r" and "\r\n" in s to "\n".
+// The conversion happens in place, but the resulting slice may be shorter.
+func convertNewlines(s []byte) []byte {
+	for i, c := range s {
+		if c != '\r' {
+			continue
+		}
+
+		src := i + 1
+		if src >= len(s) || s[src] != '\n' {
+			s[i] = '\n'
+			continue
+		}
+
+		dst := i
+		for src < len(s) {
+			if s[src] == '\r' {
+				if src+1 < len(s) && s[src+1] == '\n' {
+					src++
+				}
+				s[dst] = '\n'
+			} else {
+				s[dst] = s[src]
+			}
+			src++
+			dst++
+		}
+		return s[:dst]
+	}
+	return s
+}
+
+var (
+	nul         = []byte("\x00")
+	replacement = []byte("\ufffd")
+)
+
+// Text returns the unescaped text of a text, comment or doctype token. The
+// contents of the returned slice may change on the next call to Next.
+func (z *Tokenizer) Text() []byte {
+	switch z.tt {
+	case TextToken, CommentToken, DoctypeToken:
+		s := z.buf[z.data.start:z.data.end]
+		z.data.start = z.raw.end
+		z.data.end = z.raw.end
+		s = convertNewlines(s)
+		if (z.convertNUL || z.tt == CommentToken) && bytes.Contains(s, nul) {
+			s = bytes.Replace(s, nul, replacement, -1)
+		}
+		if !z.textIsRaw {
+			s = unescape(s, false)
+		}
+		return s
+	}
+	return nil
+}
+
+// TagName returns the lower-cased name of a tag token (the `img` out of
+// `<IMG SRC="foo">`) and whether the tag has attributes.
+// The contents of the returned slice may change on the next call to Next.
+func (z *Tokenizer) TagName() (name []byte, hasAttr bool) {
+	if z.data.start < z.data.end {
+		switch z.tt {
+		case StartTagToken, EndTagToken, SelfClosingTagToken:
+			s := z.buf[z.data.start:z.data.end]
+			z.data.start = z.raw.end
+			z.data.end = z.raw.end
+			return lower(s), z.nAttrReturned < len(z.attr)
+		}
+	}
+	return nil, false
+}
+
+// TagAttr returns the lower-cased key and unescaped value of the next unparsed
+// attribute for the current tag token and whether there are more attributes.
+// The contents of the returned slices may change on the next call to Next.
+func (z *Tokenizer) TagAttr() (key, val []byte, moreAttr bool) {
+	if z.nAttrReturned < len(z.attr) {
+		switch z.tt {
+		case StartTagToken, SelfClosingTagToken:
+			x := z.attr[z.nAttrReturned]
+			z.nAttrReturned++
+			key = z.buf[x[0].start:x[0].end]
+			val = z.buf[x[1].start:x[1].end]
+			return lower(key), unescape(convertNewlines(val), true), z.nAttrReturned < len(z.attr)
+		}
+	}
+	return nil, nil, false
+}
+
+// Token returns the current Token. The result's Data and Attr values remain
+// valid after subsequent Next calls.
+func (z *Tokenizer) Token() Token {
+	t := Token{Type: z.tt}
+	switch z.tt {
+	case TextToken, CommentToken, DoctypeToken:
+		t.Data = string(z.Text())
+	case StartTagToken, SelfClosingTagToken, EndTagToken:
+		name, moreAttr := z.TagName()
+		for moreAttr {
+			var key, val []byte
+			key, val, moreAttr = z.TagAttr()
+			t.Attr = append(t.Attr, Attribute{"", atom.String(key), string(val)})
+		}
+		if a := atom.Lookup(name); a != 0 {
+			t.DataAtom, t.Data = a, a.String()
+		} else {
+			t.DataAtom, t.Data = 0, string(name)
+		}
+	}
+	return t
+}
+
+// SetMaxBuf sets a limit on the amount of data buffered during tokenization.
+// A value of 0 means unlimited.
+func (z *Tokenizer) SetMaxBuf(n int) {
+	z.maxBuf = n
+}
+
+// NewTokenizer returns a new HTML Tokenizer for the given Reader.
+// The input is assumed to be UTF-8 encoded.
+func NewTokenizer(r io.Reader) *Tokenizer {
+	return NewTokenizerFragment(r, "")
+}
+
+// NewTokenizerFragment returns a new HTML Tokenizer for the given Reader, for
+// tokenizing an existing element's InnerHTML fragment. contextTag is that
+// element's tag, such as "div" or "iframe".
+//
+// For example, how the InnerHTML "a<b" is tokenized depends on whether it is
+// for a <p> tag or a <script> tag.
+//
+// The input is assumed to be UTF-8 encoded.
+func NewTokenizerFragment(r io.Reader, contextTag string) *Tokenizer {
+	z := &Tokenizer{
+		r:   r,
+		buf: make([]byte, 0, 4096),
+	}
+	if contextTag != "" {
+		switch s := strings.ToLower(contextTag); s {
+		case "iframe", "noembed", "noframes", "noscript", "plaintext", "script", "style", "title", "textarea", "xmp":
+			z.rawTag = s
+		}
+	}
+	return z
+}