// 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 ( "errors" "fmt" "io" "strings" a "golang.org/x/net/html/atom" ) // A parser implements the HTML5 parsing algorithm: // https://html.spec.whatwg.org/multipage/syntax.html#tree-construction type parser struct { // tokenizer provides the tokens for the parser. tokenizer *Tokenizer // tok is the most recently read token. tok Token // Self-closing tags like
are treated as start tags, except that // hasSelfClosingToken is set while they are being processed. hasSelfClosingToken bool // doc is the document root element. doc *Node // The stack of open elements (section 12.2.4.2) and active formatting // elements (section 12.2.4.3). oe, afe nodeStack // Element pointers (section 12.2.4.4). head, form *Node // Other parsing state flags (section 12.2.4.5). scripting, framesetOK bool // The stack of template insertion modes templateStack insertionModeStack // im is the current insertion mode. im insertionMode // originalIM is the insertion mode to go back to after completing a text // or inTableText insertion mode. originalIM insertionMode // fosterParenting is whether new elements should be inserted according to // the foster parenting rules (section 12.2.6.1). fosterParenting bool // quirks is whether the parser is operating in "quirks mode." quirks bool // fragment is whether the parser is parsing an HTML fragment. fragment bool // context is the context element when parsing an HTML fragment // (section 12.4). context *Node } func (p *parser) top() *Node { if n := p.oe.top(); n != nil { return n } return p.doc } // Stop tags for use in popUntil. These come from section 12.2.4.2. var ( defaultScopeStopTags = map[string][]a.Atom{ "": {a.Applet, a.Caption, a.Html, a.Table, a.Td, a.Th, a.Marquee, a.Object, a.Template}, "math": {a.AnnotationXml, a.Mi, a.Mn, a.Mo, a.Ms, a.Mtext}, "svg": {a.Desc, a.ForeignObject, a.Title}, } ) type scope int const ( defaultScope scope = iota listItemScope buttonScope tableScope tableRowScope tableBodyScope selectScope ) // popUntil pops the stack of open elements at the highest element whose tag // is in matchTags, provided there is no higher element in the scope's stop // tags (as defined in section 12.2.4.2). It returns whether or not there was // such an element. If there was not, popUntil leaves the stack unchanged. // // For example, the set of stop tags for table scope is: "html", "table". If // the stack was: // ["html", "body", "font", "table", "b", "i", "u"] // then popUntil(tableScope, "font") would return false, but // popUntil(tableScope, "i") would return true and the stack would become: // ["html", "body", "font", "table", "b"] // // If an element's tag is in both the stop tags and matchTags, then the stack // will be popped and the function returns true (provided, of course, there was // no higher element in the stack that was also in the stop tags). For example, // popUntil(tableScope, "table") returns true and leaves: // ["html", "body", "font"] func (p *parser) popUntil(s scope, matchTags ...a.Atom) bool { if i := p.indexOfElementInScope(s, matchTags...); i != -1 { p.oe = p.oe[:i] return true } return false } // indexOfElementInScope returns the index in p.oe of the highest element whose // tag is in matchTags that is in scope. If no matching element is in scope, it // returns -1. func (p *parser) indexOfElementInScope(s scope, matchTags ...a.Atom) int { for i := len(p.oe) - 1; i >= 0; i-- { tagAtom := p.oe[i].DataAtom if p.oe[i].Namespace == "" { for _, t := range matchTags { if t == tagAtom { return i } } switch s { case defaultScope: // No-op. case listItemScope: if tagAtom == a.Ol || tagAtom == a.Ul { return -1 } case buttonScope: if tagAtom == a.Button { return -1 } case tableScope: if tagAtom == a.Html || tagAtom == a.Table || tagAtom == a.Template { return -1 } case selectScope: if tagAtom != a.Optgroup && tagAtom != a.Option { return -1 } default: panic("unreachable") } } switch s { case defaultScope, listItemScope, buttonScope: for _, t := range defaultScopeStopTags[p.oe[i].Namespace] { if t == tagAtom { return -1 } } } } return -1 } // elementInScope is like popUntil, except that it doesn't modify the stack of // open elements. func (p *parser) elementInScope(s scope, matchTags ...a.Atom) bool { return p.indexOfElementInScope(s, matchTags...) != -1 } // clearStackToContext pops elements off the stack of open elements until a // scope-defined element is found. func (p *parser) clearStackToContext(s scope) { for i := len(p.oe) - 1; i >= 0; i-- { tagAtom := p.oe[i].DataAtom switch s { case tableScope: if tagAtom == a.Html || tagAtom == a.Table || tagAtom == a.Template { p.oe = p.oe[:i+1] return } case tableRowScope: if tagAtom == a.Html || tagAtom == a.Tr || tagAtom == a.Template { p.oe = p.oe[:i+1] return } case tableBodyScope: if tagAtom == a.Html || tagAtom == a.Tbody || tagAtom == a.Tfoot || tagAtom == a.Thead || tagAtom == a.Template { p.oe = p.oe[:i+1] return } default: panic("unreachable") } } } // generateImpliedEndTags pops nodes off the stack of open elements as long as // the top node has a tag name of dd, dt, li, optgroup, option, p, rb, rp, rt or rtc. // If exceptions are specified, nodes with that name will not be popped off. func (p *parser) generateImpliedEndTags(exceptions ...string) { var i int loop: for i = len(p.oe) - 1; i >= 0; i-- { n := p.oe[i] if n.Type == ElementNode { switch n.DataAtom { case a.Dd, a.Dt, a.Li, a.Optgroup, a.Option, a.P, a.Rb, a.Rp, a.Rt, a.Rtc: for _, except := range exceptions { if n.Data == except { break loop } } continue } } break } p.oe = p.oe[:i+1] } // generateAllImpliedEndTags pops nodes off the stack of open elements as long as // the top node has a tag name of caption, colgroup, dd, div, dt, li, optgroup, option, p, rb, // rp, rt, rtc, span, tbody, td, tfoot, th, thead or tr. func (p *parser) generateAllImpliedEndTags() { var i int for i = len(p.oe) - 1; i >= 0; i-- { n := p.oe[i] if n.Type == ElementNode { switch n.DataAtom { // TODO: remove this divergence from the HTML5 spec case a.Caption, a.Colgroup, a.Dd, a.Div, a.Dt, a.Li, a.Optgroup, a.Option, a.P, a.Rb, a.Rp, a.Rt, a.Rtc, a.Span, a.Tbody, a.Td, a.Tfoot, a.Th, a.Thead, a.Tr: continue } } break } p.oe = p.oe[:i+1] } // addChild adds a child node n to the top element, and pushes n onto the stack // of open elements if it is an element node. func (p *parser) addChild(n *Node) { if p.shouldFosterParent() { p.fosterParent(n) } else { p.top().AppendChild(n) } if n.Type == ElementNode { p.oe = append(p.oe, n) } } // shouldFosterParent returns whether the next node to be added should be // foster parented. func (p *parser) shouldFosterParent() bool { if p.fosterParenting { switch p.top().DataAtom { case a.Table, a.Tbody, a.Tfoot, a.Thead, a.Tr: return true } } return false } // fosterParent adds a child node according to the foster parenting rules. // Section 12.2.6.1, "foster parenting". func (p *parser) fosterParent(n *Node) { var table, parent, prev, template *Node var i int for i = len(p.oe) - 1; i >= 0; i-- { if p.oe[i].DataAtom == a.Table { table = p.oe[i] break } } var j int for j = len(p.oe) - 1; j >= 0; j-- { if p.oe[j].DataAtom == a.Template { template = p.oe[j] break } } if template != nil && (table == nil || j < i) { template.AppendChild(n) return } if table == nil { // The foster parent is the html element. parent = p.oe[0] } else { parent = table.Parent } if parent == nil { parent = p.oe[i-1] } if table != nil { prev = table.PrevSibling } else { prev = parent.LastChild } if prev != nil && prev.Type == TextNode && n.Type == TextNode { prev.Data += n.Data return } parent.InsertBefore(n, table) } // addText adds text to the preceding node if it is a text node, or else it // calls addChild with a new text node. func (p *parser) addText(text string) { if text == "" { return } if p.shouldFosterParent() { p.fosterParent(&Node{ Type: TextNode, Data: text, }) return } t := p.top() if n := t.LastChild; n != nil && n.Type == TextNode { n.Data += text return } p.addChild(&Node{ Type: TextNode, Data: text, }) } // addElement adds a child element based on the current token. func (p *parser) addElement() { p.addChild(&Node{ Type: ElementNode, DataAtom: p.tok.DataAtom, Data: p.tok.Data, Attr: p.tok.Attr, }) } // Section 12.2.4.3. func (p *parser) addFormattingElement() { tagAtom, attr := p.tok.DataAtom, p.tok.Attr p.addElement() // Implement the Noah's Ark clause, but with three per family instead of two. identicalElements := 0 findIdenticalElements: for i := len(p.afe) - 1; i >= 0; i-- { n := p.afe[i] if n.Type == scopeMarkerNode { break } if n.Type != ElementNode { continue } if n.Namespace != "" { continue } if n.DataAtom != tagAtom { continue } if len(n.Attr) != len(attr) { continue } compareAttributes: for _, t0 := range n.Attr { for _, t1 := range attr { if t0.Key == t1.Key && t0.Namespace == t1.Namespace && t0.Val == t1.Val { // Found a match for this attribute, continue with the next attribute. continue compareAttributes } } // If we get here, there is no attribute that matches a. // Therefore the element is not identical to the new one. continue findIdenticalElements } identicalElements++ if identicalElements >= 3 { p.afe.remove(n) } } p.afe = append(p.afe, p.top()) } // Section 12.2.4.3. func (p *parser) clearActiveFormattingElements() { for { n := p.afe.pop() if len(p.afe) == 0 || n.Type == scopeMarkerNode { return } } } // Section 12.2.4.3. func (p *parser) reconstructActiveFormattingElements() { n := p.afe.top() if n == nil { return } if n.Type == scopeMarkerNode || p.oe.index(n) != -1 { return } i := len(p.afe) - 1 for n.Type != scopeMarkerNode && p.oe.index(n) == -1 { if i == 0 { i = -1 break } i-- n = p.afe[i] } for { i++ clone := p.afe[i].clone() p.addChild(clone) p.afe[i] = clone if i == len(p.afe)-1 { break } } } // Section 12.2.5. func (p *parser) acknowledgeSelfClosingTag() { p.hasSelfClosingToken = false } // An insertion mode (section 12.2.4.1) is the state transition function from // a particular state in the HTML5 parser's state machine. It updates the // parser's fields depending on parser.tok (where ErrorToken means EOF). // It returns whether the token was consumed. type insertionMode func(*parser) bool // setOriginalIM sets the insertion mode to return to after completing a text or // inTableText insertion mode. // Section 12.2.4.1, "using the rules for". func (p *parser) setOriginalIM() { if p.originalIM != nil { panic("html: bad parser state: originalIM was set twice") } p.originalIM = p.im } // Section 12.2.4.1, "reset the insertion mode". func (p *parser) resetInsertionMode() { for i := len(p.oe) - 1; i >= 0; i-- { n := p.oe[i] last := i == 0 if last && p.context != nil { n = p.context } switch n.DataAtom { case a.Select: if !last { for ancestor, first := n, p.oe[0]; ancestor != first; { if ancestor == first { break } ancestor = p.oe[p.oe.index(ancestor)-1] switch ancestor.DataAtom { case a.Template: p.im = inSelectIM return case a.Table: p.im = inSelectInTableIM return } } } p.im = inSelectIM case a.Td, a.Th: // TODO: remove this divergence from the HTML5 spec. // // See https://bugs.chromium.org/p/chromium/issues/detail?id=829668 p.im = inCellIM case a.Tr: p.im = inRowIM case a.Tbody, a.Thead, a.Tfoot: p.im = inTableBodyIM case a.Caption: p.im = inCaptionIM case a.Colgroup: p.im = inColumnGroupIM case a.Table: p.im = inTableIM case a.Template: p.im = p.templateStack.top() case a.Head: // TODO: remove this divergence from the HTML5 spec. // // See https://bugs.chromium.org/p/chromium/issues/detail?id=829668 p.im = inHeadIM case a.Body: p.im = inBodyIM case a.Frameset: p.im = inFramesetIM case a.Html: if p.head == nil { p.im = beforeHeadIM } else { p.im = afterHeadIM } default: if last { p.im = inBodyIM return } continue } return } } const whitespace = " \t\r\n\f" // Section 12.2.6.4.1. func initialIM(p *parser) bool { switch p.tok.Type { case TextToken: p.tok.Data = strings.TrimLeft(p.tok.Data, whitespace) if len(p.tok.Data) == 0 { // It was all whitespace, so ignore it. return true } case CommentToken: p.doc.AppendChild(&Node{ Type: CommentNode, Data: p.tok.Data, }) return true case DoctypeToken: n, quirks := parseDoctype(p.tok.Data) p.doc.AppendChild(n) p.quirks = quirks p.im = beforeHTMLIM return true } p.quirks = true p.im = beforeHTMLIM return false } // Section 12.2.6.4.2. func beforeHTMLIM(p *parser) bool { switch p.tok.Type { case DoctypeToken: // Ignore the token. return true case TextToken: p.tok.Data = strings.TrimLeft(p.tok.Data, whitespace) if len(p.tok.Data) == 0 { // It was all whitespace, so ignore it. return true } case StartTagToken: if p.tok.DataAtom == a.Html { p.addElement() p.im = beforeHeadIM return true } case EndTagToken: switch p.tok.DataAtom { case a.Head, a.Body, a.Html, a.Br: p.parseImpliedToken(StartTagToken, a.Html, a.Html.String()) return false default: // Ignore the token. return true } case CommentToken: p.doc.AppendChild(&Node{ Type: CommentNode, Data: p.tok.Data, }) return true } p.parseImpliedToken(StartTagToken, a.Html, a.Html.String()) return false } // Section 12.2.6.4.3. func beforeHeadIM(p *parser) bool { switch p.tok.Type { case TextToken: p.tok.Data = strings.TrimLeft(p.tok.Data, whitespace) if len(p.tok.Data) == 0 { // It was all whitespace, so ignore it. return true } case StartTagToken: switch p.tok.DataAtom { case a.Head: p.addElement() p.head = p.top() p.im = inHeadIM return true case a.Html: return inBodyIM(p) } case EndTagToken: switch p.tok.DataAtom { case a.Head, a.Body, a.Html, a.Br: p.parseImpliedToken(StartTagToken, a.Head, a.Head.String()) return false default: // Ignore the token. return true } case CommentToken: p.addChild(&Node{ Type: CommentNode, Data: p.tok.Data, }) return true case DoctypeToken: // Ignore the token. return true } p.parseImpliedToken(StartTagToken, a.Head, a.Head.String()) return false } // Section 12.2.6.4.4. func inHeadIM(p *parser) bool { switch p.tok.Type { case TextToken: s := strings.TrimLeft(p.tok.Data, whitespace) if len(s) < len(p.tok.Data) { // Add the initial whitespace to the current node. p.addText(p.tok.Data[:len(p.tok.Data)-len(s)]) if s == "" { return true } p.tok.Data = s } case StartTagToken: switch p.tok.DataAtom { case a.Html: return inBodyIM(p) case a.Base, a.Basefont, a.Bgsound, a.Command, a.Link, a.Meta: p.addElement() p.oe.pop() p.acknowledgeSelfClosingTag() return true case a.Script, a.Title, a.Noscript, a.Noframes, a.Style: p.addElement() p.setOriginalIM() p.im = textIM return true case a.Head: // Ignore the token. return true case a.Template: p.addElement() p.afe = append(p.afe, &scopeMarker) p.framesetOK = false p.im = inTemplateIM p.templateStack = append(p.templateStack, inTemplateIM) return true } case EndTagToken: switch p.tok.DataAtom { case a.Head: p.oe.pop() p.im = afterHeadIM return true case a.Body, a.Html, a.Br: p.parseImpliedToken(EndTagToken, a.Head, a.Head.String()) return false case a.Template: if !p.oe.contains(a.Template) { return true } p.generateAllImpliedEndTags() if n := p.oe.top(); n.DataAtom != a.Template { return true } p.popUntil(defaultScope, a.Template) p.clearActiveFormattingElements() p.templateStack.pop() p.resetInsertionMode() return true default: // Ignore the token. return true } case CommentToken: p.addChild(&Node{ Type: CommentNode, Data: p.tok.Data, }) return true case DoctypeToken: // Ignore the token. return true } p.parseImpliedToken(EndTagToken, a.Head, a.Head.String()) return false } // Section 12.2.6.4.6. func afterHeadIM(p *parser) bool { switch p.tok.Type { case TextToken: s := strings.TrimLeft(p.tok.Data, whitespace) if len(s) < len(p.tok.Data) { // Add the initial whitespace to the current node. p.addText(p.tok.Data[:len(p.tok.Data)-len(s)]) if s == "" { return true } p.tok.Data = s } case StartTagToken: switch p.tok.DataAtom { case a.Html: return inBodyIM(p) case a.Body: p.addElement() p.framesetOK = false p.im = inBodyIM return true case a.Frameset: p.addElement() p.im = inFramesetIM return true case a.Base, a.Basefont, a.Bgsound, a.Link, a.Meta, a.Noframes, a.Script, a.Style, a.Template, a.Title: p.oe = append(p.oe, p.head) defer p.oe.remove(p.head) return inHeadIM(p) case a.Head: // Ignore the token. return true } case EndTagToken: switch p.tok.DataAtom { case a.Body, a.Html, a.Br: // Drop down to creating an implied tag. case a.Template: return inHeadIM(p) default: // Ignore the token. return true } case CommentToken: p.addChild(&Node{ Type: CommentNode, Data: p.tok.Data, }) return true case DoctypeToken: // Ignore the token. return true } p.parseImpliedToken(StartTagToken, a.Body, a.Body.String()) p.framesetOK = true return false } // copyAttributes copies attributes of src not found on dst to dst. func copyAttributes(dst *Node, src Token) { if len(src.Attr) == 0 { return } attr := map[string]string{} for _, t := range dst.Attr { attr[t.Key] = t.Val } for _, t := range src.Attr { if _, ok := attr[t.Key]; !ok { dst.Attr = append(dst.Attr, t) attr[t.Key] = t.Val } } } // Section 12.2.6.4.7. func inBodyIM(p *parser) bool { switch p.tok.Type { case TextToken: d := p.tok.Data switch n := p.oe.top(); n.DataAtom { case a.Pre, a.Listing: if n.FirstChild == nil { // Ignore a newline at the start of a
 block.
				if d != "" && d[0] == '\r' {
					d = d[1:]
				}
				if d != "" && d[0] == '\n' {
					d = d[1:]
				}
			}
		}
		d = strings.Replace(d, "\x00", "", -1)
		if d == "" {
			return true
		}
		p.reconstructActiveFormattingElements()
		p.addText(d)
		if p.framesetOK && strings.TrimLeft(d, whitespace) != "" {
			// There were non-whitespace characters inserted.
			p.framesetOK = false
		}
	case StartTagToken:
		switch p.tok.DataAtom {
		case a.Html:
			if p.oe.contains(a.Template) {
				return true
			}
			copyAttributes(p.oe[0], p.tok)
		case a.Base, a.Basefont, a.Bgsound, a.Command, a.Link, a.Meta, a.Noframes, a.Script, a.Style, a.Template, a.Title:
			return inHeadIM(p)
		case a.Body:
			if p.oe.contains(a.Template) {
				return true
			}
			if len(p.oe) >= 2 {
				body := p.oe[1]
				if body.Type == ElementNode && body.DataAtom == a.Body {
					p.framesetOK = false
					copyAttributes(body, p.tok)
				}
			}
		case a.Frameset:
			if !p.framesetOK || len(p.oe) < 2 || p.oe[1].DataAtom != a.Body {
				// Ignore the token.
				return true
			}
			body := p.oe[1]
			if body.Parent != nil {
				body.Parent.RemoveChild(body)
			}
			p.oe = p.oe[:1]
			p.addElement()
			p.im = inFramesetIM
			return true
		case a.Address, a.Article, a.Aside, a.Blockquote, a.Center, a.Details, a.Dir, a.Div, a.Dl, a.Fieldset, a.Figcaption, a.Figure, a.Footer, a.Header, a.Hgroup, a.Menu, a.Nav, a.Ol, a.P, a.Section, a.Summary, a.Ul:
			p.popUntil(buttonScope, a.P)
			p.addElement()
		case a.H1, a.H2, a.H3, a.H4, a.H5, a.H6:
			p.popUntil(buttonScope, a.P)
			switch n := p.top(); n.DataAtom {
			case a.H1, a.H2, a.H3, a.H4, a.H5, a.H6:
				p.oe.pop()
			}
			p.addElement()
		case a.Pre, a.Listing:
			p.popUntil(buttonScope, a.P)
			p.addElement()
			// The newline, if any, will be dealt with by the TextToken case.
			p.framesetOK = false
		case a.Form:
			if p.form != nil && !p.oe.contains(a.Template) {
				// Ignore the token
				return true
			}
			p.popUntil(buttonScope, a.P)
			p.addElement()
			if !p.oe.contains(a.Template) {
				p.form = p.top()
			}
		case a.Li:
			p.framesetOK = false
			for i := len(p.oe) - 1; i >= 0; i-- {
				node := p.oe[i]
				switch node.DataAtom {
				case a.Li:
					p.oe = p.oe[:i]
				case a.Address, a.Div, a.P:
					continue
				default:
					if !isSpecialElement(node) {
						continue
					}
				}
				break
			}
			p.popUntil(buttonScope, a.P)
			p.addElement()
		case a.Dd, a.Dt:
			p.framesetOK = false
			for i := len(p.oe) - 1; i >= 0; i-- {
				node := p.oe[i]
				switch node.DataAtom {
				case a.Dd, a.Dt:
					p.oe = p.oe[:i]
				case a.Address, a.Div, a.P:
					continue
				default:
					if !isSpecialElement(node) {
						continue
					}
				}
				break
			}
			p.popUntil(buttonScope, a.P)
			p.addElement()
		case a.Plaintext:
			p.popUntil(buttonScope, a.P)
			p.addElement()
		case a.Button:
			p.popUntil(defaultScope, a.Button)
			p.reconstructActiveFormattingElements()
			p.addElement()
			p.framesetOK = false
		case a.A:
			for i := len(p.afe) - 1; i >= 0 && p.afe[i].Type != scopeMarkerNode; i-- {
				if n := p.afe[i]; n.Type == ElementNode && n.DataAtom == a.A {
					p.inBodyEndTagFormatting(a.A)
					p.oe.remove(n)
					p.afe.remove(n)
					break
				}
			}
			p.reconstructActiveFormattingElements()
			p.addFormattingElement()
		case a.B, a.Big, a.Code, a.Em, a.Font, a.I, a.S, a.Small, a.Strike, a.Strong, a.Tt, a.U:
			p.reconstructActiveFormattingElements()
			p.addFormattingElement()
		case a.Nobr:
			p.reconstructActiveFormattingElements()
			if p.elementInScope(defaultScope, a.Nobr) {
				p.inBodyEndTagFormatting(a.Nobr)
				p.reconstructActiveFormattingElements()
			}
			p.addFormattingElement()
		case a.Applet, a.Marquee, a.Object:
			p.reconstructActiveFormattingElements()
			p.addElement()
			p.afe = append(p.afe, &scopeMarker)
			p.framesetOK = false
		case a.Table:
			if !p.quirks {
				p.popUntil(buttonScope, a.P)
			}
			p.addElement()
			p.framesetOK = false
			p.im = inTableIM
			return true
		case a.Area, a.Br, a.Embed, a.Img, a.Input, a.Keygen, a.Wbr:
			p.reconstructActiveFormattingElements()
			p.addElement()
			p.oe.pop()
			p.acknowledgeSelfClosingTag()
			if p.tok.DataAtom == a.Input {
				for _, t := range p.tok.Attr {
					if t.Key == "type" {
						if strings.ToLower(t.Val) == "hidden" {
							// Skip setting framesetOK = false
							return true
						}
					}
				}
			}
			p.framesetOK = false
		case a.Param, a.Source, a.Track:
			p.addElement()
			p.oe.pop()
			p.acknowledgeSelfClosingTag()
		case a.Hr:
			p.popUntil(buttonScope, a.P)
			p.addElement()
			p.oe.pop()
			p.acknowledgeSelfClosingTag()
			p.framesetOK = false
		case a.Image:
			p.tok.DataAtom = a.Img
			p.tok.Data = a.Img.String()
			return false
		case a.Isindex:
			if p.form != nil {
				// Ignore the token.
				return true
			}
			action := ""
			prompt := "This is a searchable index. Enter search keywords: "
			attr := []Attribute{{Key: "name", Val: "isindex"}}
			for _, t := range p.tok.Attr {
				switch t.Key {
				case "action":
					action = t.Val
				case "name":
					// Ignore the attribute.
				case "prompt":
					prompt = t.Val
				default:
					attr = append(attr, t)
				}
			}
			p.acknowledgeSelfClosingTag()
			p.popUntil(buttonScope, a.P)
			p.parseImpliedToken(StartTagToken, a.Form, a.Form.String())
			if action != "" {
				p.form.Attr = []Attribute{{Key: "action", Val: action}}
			}
			p.parseImpliedToken(StartTagToken, a.Hr, a.Hr.String())
			p.parseImpliedToken(StartTagToken, a.Label, a.Label.String())
			p.addText(prompt)
			p.addChild(&Node{
				Type:     ElementNode,
				DataAtom: a.Input,
				Data:     a.Input.String(),
				Attr:     attr,
			})
			p.oe.pop()
			p.parseImpliedToken(EndTagToken, a.Label, a.Label.String())
			p.parseImpliedToken(StartTagToken, a.Hr, a.Hr.String())
			p.parseImpliedToken(EndTagToken, a.Form, a.Form.String())
		case a.Textarea:
			p.addElement()
			p.setOriginalIM()
			p.framesetOK = false
			p.im = textIM
		case a.Xmp:
			p.popUntil(buttonScope, a.P)
			p.reconstructActiveFormattingElements()
			p.framesetOK = false
			p.addElement()
			p.setOriginalIM()
			p.im = textIM
		case a.Iframe:
			p.framesetOK = false
			p.addElement()
			p.setOriginalIM()
			p.im = textIM
		case a.Noembed, a.Noscript:
			p.addElement()
			p.setOriginalIM()
			p.im = textIM
		case a.Select:
			p.reconstructActiveFormattingElements()
			p.addElement()
			p.framesetOK = false
			p.im = inSelectIM
			return true
		case a.Optgroup, a.Option:
			if p.top().DataAtom == a.Option {
				p.oe.pop()
			}
			p.reconstructActiveFormattingElements()
			p.addElement()
		case a.Rb, a.Rtc:
			if p.elementInScope(defaultScope, a.Ruby) {
				p.generateImpliedEndTags()
			}
			p.addElement()
		case a.Rp, a.Rt:
			if p.elementInScope(defaultScope, a.Ruby) {
				p.generateImpliedEndTags("rtc")
			}
			p.addElement()
		case a.Math, a.Svg:
			p.reconstructActiveFormattingElements()
			if p.tok.DataAtom == a.Math {
				adjustAttributeNames(p.tok.Attr, mathMLAttributeAdjustments)
			} else {
				adjustAttributeNames(p.tok.Attr, svgAttributeAdjustments)
			}
			adjustForeignAttributes(p.tok.Attr)
			p.addElement()
			p.top().Namespace = p.tok.Data
			if p.hasSelfClosingToken {
				p.oe.pop()
				p.acknowledgeSelfClosingTag()
			}
			return true
		case a.Frame:
			// TODO: remove this divergence from the HTML5 spec.
			if p.oe.contains(a.Template) {
				p.addElement()
				return true
			}
		case a.Caption, a.Col, a.Colgroup, a.Head, a.Tbody, a.Td, a.Tfoot, a.Th, a.Thead, a.Tr:
			// Ignore the token.
		default:
			p.reconstructActiveFormattingElements()
			p.addElement()
		}
	case EndTagToken:
		switch p.tok.DataAtom {
		case a.Body:
			if p.elementInScope(defaultScope, a.Body) {
				p.im = afterBodyIM
			}
		case a.Html:
			if p.elementInScope(defaultScope, a.Body) {
				p.parseImpliedToken(EndTagToken, a.Body, a.Body.String())
				return false
			}
			return true
		case a.Address, a.Article, a.Aside, a.Blockquote, a.Button, a.Center, a.Details, a.Dir, a.Div, a.Dl, a.Fieldset, a.Figcaption, a.Figure, a.Footer, a.Header, a.Hgroup, a.Listing, a.Menu, a.Nav, a.Ol, a.Pre, a.Section, a.Summary, a.Ul:
			p.popUntil(defaultScope, p.tok.DataAtom)
		case a.Form:
			if p.oe.contains(a.Template) {
				i := p.indexOfElementInScope(defaultScope, a.Form)
				if i == -1 {
					// Ignore the token.
					return true
				}
				p.generateImpliedEndTags()
				if p.oe[i].DataAtom != a.Form {
					// Ignore the token.
					return true
				}
				p.popUntil(defaultScope, a.Form)
			} else {
				node := p.form
				p.form = nil
				i := p.indexOfElementInScope(defaultScope, a.Form)
				if node == nil || i == -1 || p.oe[i] != node {
					// Ignore the token.
					return true
				}
				p.generateImpliedEndTags()
				p.oe.remove(node)
			}
		case a.P:
			if !p.elementInScope(buttonScope, a.P) {
				p.parseImpliedToken(StartTagToken, a.P, a.P.String())
			}
			p.popUntil(buttonScope, a.P)
		case a.Li:
			p.popUntil(listItemScope, a.Li)
		case a.Dd, a.Dt:
			p.popUntil(defaultScope, p.tok.DataAtom)
		case a.H1, a.H2, a.H3, a.H4, a.H5, a.H6:
			p.popUntil(defaultScope, a.H1, a.H2, a.H3, a.H4, a.H5, a.H6)
		case a.A, a.B, a.Big, a.Code, a.Em, a.Font, a.I, a.Nobr, a.S, a.Small, a.Strike, a.Strong, a.Tt, a.U:
			p.inBodyEndTagFormatting(p.tok.DataAtom)
		case a.Applet, a.Marquee, a.Object:
			if p.popUntil(defaultScope, p.tok.DataAtom) {
				p.clearActiveFormattingElements()
			}
		case a.Br:
			p.tok.Type = StartTagToken
			return false
		case a.Template:
			return inHeadIM(p)
		default:
			p.inBodyEndTagOther(p.tok.DataAtom)
		}
	case CommentToken:
		p.addChild(&Node{
			Type: CommentNode,
			Data: p.tok.Data,
		})
	case ErrorToken:
		// TODO: remove this divergence from the HTML5 spec.
		if len(p.templateStack) > 0 {
			p.im = inTemplateIM
			return false
		} else {
			for _, e := range p.oe {
				switch e.DataAtom {
				case a.Dd, a.Dt, a.Li, a.Optgroup, a.Option, a.P, a.Rb, a.Rp, a.Rt, a.Rtc, a.Tbody, a.Td, a.Tfoot, a.Th,
					a.Thead, a.Tr, a.Body, a.Html:
				default:
					return true
				}
			}
		}
	}

	return true
}

func (p *parser) inBodyEndTagFormatting(tagAtom a.Atom) {
	// This is the "adoption agency" algorithm, described at
	// https://html.spec.whatwg.org/multipage/syntax.html#adoptionAgency

	// TODO: this is a fairly literal line-by-line translation of that algorithm.
	// Once the code successfully parses the comprehensive test suite, we should
	// refactor this code to be more idiomatic.

	// Steps 1-4. The outer loop.
	for i := 0; i < 8; i++ {
		// Step 5. Find the formatting element.
		var formattingElement *Node
		for j := len(p.afe) - 1; j >= 0; j-- {
			if p.afe[j].Type == scopeMarkerNode {
				break
			}
			if p.afe[j].DataAtom == tagAtom {
				formattingElement = p.afe[j]
				break
			}
		}
		if formattingElement == nil {
			p.inBodyEndTagOther(tagAtom)
			return
		}
		feIndex := p.oe.index(formattingElement)
		if feIndex == -1 {
			p.afe.remove(formattingElement)
			return
		}
		if !p.elementInScope(defaultScope, tagAtom) {
			// Ignore the tag.
			return
		}

		// Steps 9-10. Find the furthest block.
		var furthestBlock *Node
		for _, e := range p.oe[feIndex:] {
			if isSpecialElement(e) {
				furthestBlock = e
				break
			}
		}
		if furthestBlock == nil {
			e := p.oe.pop()
			for e != formattingElement {
				e = p.oe.pop()
			}
			p.afe.remove(e)
			return
		}

		// Steps 11-12. Find the common ancestor and bookmark node.
		commonAncestor := p.oe[feIndex-1]
		bookmark := p.afe.index(formattingElement)

		// Step 13. The inner loop. Find the lastNode to reparent.
		lastNode := furthestBlock
		node := furthestBlock
		x := p.oe.index(node)
		// Steps 13.1-13.2
		for j := 0; j < 3; j++ {
			// Step 13.3.
			x--
			node = p.oe[x]
			// Step 13.4 - 13.5.
			if p.afe.index(node) == -1 {
				p.oe.remove(node)
				continue
			}
			// Step 13.6.
			if node == formattingElement {
				break
			}
			// Step 13.7.
			clone := node.clone()
			p.afe[p.afe.index(node)] = clone
			p.oe[p.oe.index(node)] = clone
			node = clone
			// Step 13.8.
			if lastNode == furthestBlock {
				bookmark = p.afe.index(node) + 1
			}
			// Step 13.9.
			if lastNode.Parent != nil {
				lastNode.Parent.RemoveChild(lastNode)
			}
			node.AppendChild(lastNode)
			// Step 13.10.
			lastNode = node
		}

		// Step 14. Reparent lastNode to the common ancestor,
		// or for misnested table nodes, to the foster parent.
		if lastNode.Parent != nil {
			lastNode.Parent.RemoveChild(lastNode)
		}
		switch commonAncestor.DataAtom {
		case a.Table, a.Tbody, a.Tfoot, a.Thead, a.Tr:
			p.fosterParent(lastNode)
		case a.Template:
			// TODO: remove namespace checking
			if commonAncestor.Namespace == "html" {
				commonAncestor = commonAncestor.LastChild
			}
			fallthrough
		default:
			commonAncestor.AppendChild(lastNode)
		}

		// Steps 15-17. Reparent nodes from the furthest block's children
		// to a clone of the formatting element.
		clone := formattingElement.clone()
		reparentChildren(clone, furthestBlock)
		furthestBlock.AppendChild(clone)

		// Step 18. Fix up the list of active formatting elements.
		if oldLoc := p.afe.index(formattingElement); oldLoc != -1 && oldLoc < bookmark {
			// Move the bookmark with the rest of the list.
			bookmark--
		}
		p.afe.remove(formattingElement)
		p.afe.insert(bookmark, clone)

		// Step 19. Fix up the stack of open elements.
		p.oe.remove(formattingElement)
		p.oe.insert(p.oe.index(furthestBlock)+1, clone)
	}
}

// inBodyEndTagOther performs the "any other end tag" algorithm for inBodyIM.
// "Any other end tag" handling from 12.2.6.5 The rules for parsing tokens in foreign content
// https://html.spec.whatwg.org/multipage/syntax.html#parsing-main-inforeign
func (p *parser) inBodyEndTagOther(tagAtom a.Atom) {
	for i := len(p.oe) - 1; i >= 0; i-- {
		if p.oe[i].DataAtom == tagAtom {
			p.oe = p.oe[:i]
			break
		}
		if isSpecialElement(p.oe[i]) {
			break
		}
	}
}

// Section 12.2.6.4.8.
func textIM(p *parser) bool {
	switch p.tok.Type {
	case ErrorToken:
		p.oe.pop()
	case TextToken:
		d := p.tok.Data
		if n := p.oe.top(); n.DataAtom == a.Textarea && n.FirstChild == nil {
			// Ignore a newline at the start of a