go vendor

vendor/code.google.com/p/cascadia/LICENSE

@@ -0,0 +1,24 @@
+Copyright (c) 2011 Andy Balholm. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without
+modification, are permitted provided that the following conditions are
+met:
+
+   * Redistributions of source code must retain the above copyright
+notice, this list of conditions and the following disclaimer.
+   * Redistributions in binary form must reproduce the above
+copyright notice, this list of conditions and the following disclaimer
+in the documentation and/or other materials provided with the
+distribution.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
+"AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
+LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR
+A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT
+OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL,
+SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT
+LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
+DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
+THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
+OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

vendor/code.google.com/p/cascadia/Makefile

@@ -0,0 +1,12 @@
+include $(GOROOT)/src/Make.inc
+
+TARG=cascadia
+
+GOFILES= \
+	parser.go \
+	selector.go \
+	
+include $(GOROOT)/src/Make.pkg
+
+format:
+	gofmt -w ${GOFILES} *_test.go

vendor/code.google.com/p/cascadia/parser.go

@@ -0,0 +1,812 @@
+// The cascadia package is an implementation of CSS selectors.
+package cascadia
+
+import (
+	"code.google.com/p/go.net/html"
+	"errors"
+	"fmt"
+	"regexp"
+	"strconv"
+	"strings"
+)
+
+// a parser for CSS selectors
+type parser struct {
+	s string // the source text
+	i int    // the current position
+}
+
+// parseEscape parses a backslash escape.
+func (p *parser) parseEscape() (result string, err error) {
+	if len(p.s) < p.i+2 || p.s[p.i] != '\\' {
+		return "", errors.New("invalid escape sequence")
+	}
+
+	start := p.i + 1
+	c := p.s[start]
+	switch {
+	case c == '\r' || c == '\n' || c == '\f':
+		return "", errors.New("escaped line ending outside string")
+	case hexDigit(c):
+		// unicode escape (hex)
+		var i int
+		for i = start; i < p.i+6 && i < len(p.s) && hexDigit(p.s[i]); i++ {
+			// empty
+		}
+		v, _ := strconv.ParseUint(p.s[start:i], 16, 21)
+		if len(p.s) > i {
+			switch p.s[i] {
+			case '\r':
+				i++
+				if len(p.s) > i && p.s[i] == '\n' {
+					i++
+				}
+			case ' ', '\t', '\n', '\f':
+				i++
+			}
+		}
+		p.i = i
+		return string(rune(v)), nil
+	}
+
+	// Return the literal character after the backslash.
+	result = p.s[start : start+1]
+	p.i += 2
+	return result, nil
+}
+
+func hexDigit(c byte) bool {
+	return '0' <= c && c <= '9' || 'a' <= c && c <= 'f' || 'A' <= c && c <= 'F'
+}
+
+// nameStart returns whether c can be the first character of an identifier
+// (not counting an initial hyphen, or an escape sequence).
+func nameStart(c byte) bool {
+	return 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' || c == '_' || c > 127
+}
+
+// nameChar returns whether c can be a character within an identifier
+// (not counting an escape sequence).
+func nameChar(c byte) bool {
+	return 'a' <= c && c <= 'z' || 'A' <= c && c <= 'Z' || c == '_' || c > 127 ||
+		c == '-' || '0' <= c && c <= '9'
+}
+
+// parseIdentifier parses an identifier.
+func (p *parser) parseIdentifier() (result string, err error) {
+	startingDash := false
+	if len(p.s) > p.i && p.s[p.i] == '-' {
+		startingDash = true
+		p.i++
+	}
+
+	if len(p.s) <= p.i {
+		return "", errors.New("expected identifier, found EOF instead")
+	}
+
+	if c := p.s[p.i]; !(nameStart(c) || c == '\\') {
+		return "", fmt.Errorf("expected identifier, found %c instead", c)
+	}
+
+	result, err = p.parseName()
+	if startingDash && err == nil {
+		result = "-" + result
+	}
+	return
+}
+
+// parseName parses a name (which is like an identifier, but doesn't have
+// extra restrictions on the first character).
+func (p *parser) parseName() (result string, err error) {
+	i := p.i
+loop:
+	for i < len(p.s) {
+		c := p.s[i]
+		switch {
+		case nameChar(c):
+			start := i
+			for i < len(p.s) && nameChar(p.s[i]) {
+				i++
+			}
+			result += p.s[start:i]
+		case c == '\\':
+			p.i = i
+			val, err := p.parseEscape()
+			if err != nil {
+				return "", err
+			}
+			i = p.i
+			result += val
+		default:
+			break loop
+		}
+	}
+
+	if result == "" {
+		return "", errors.New("expected name, found EOF instead")
+	}
+
+	p.i = i
+	return result, nil
+}
+
+// parseString parses a single- or double-quoted string.
+func (p *parser) parseString() (result string, err error) {
+	i := p.i
+	if len(p.s) < i+2 {
+		return "", errors.New("expected string, found EOF instead")
+	}
+
+	quote := p.s[i]
+	i++
+
+loop:
+	for i < len(p.s) {
+		switch p.s[i] {
+		case '\\':
+			if len(p.s) > i+1 {
+				switch c := p.s[i+1]; c {
+				case '\r':
+					if len(p.s) > i+2 && p.s[i+2] == '\n' {
+						i += 3
+						continue loop
+					}
+					fallthrough
+				case '\n', '\f':
+					i += 2
+					continue loop
+				}
+			}
+			p.i = i
+			val, err := p.parseEscape()
+			if err != nil {
+				return "", err
+			}
+			i = p.i
+			result += val
+		case quote:
+			break loop
+		case '\r', '\n', '\f':
+			return "", errors.New("unexpected end of line in string")
+		default:
+			start := i
+			for i < len(p.s) {
+				if c := p.s[i]; c == quote || c == '\\' || c == '\r' || c == '\n' || c == '\f' {
+					break
+				}
+				i++
+			}
+			result += p.s[start:i]
+		}
+	}
+
+	if i >= len(p.s) {
+		return "", errors.New("EOF in string")
+	}
+
+	// Consume the final quote.
+	i++
+
+	p.i = i
+	return result, nil
+}
+
+// parseRegex parses a regular expression; the end is defined by encountering an
+// unmatched closing ')' or ']' which is not consumed
+func (p *parser) parseRegex() (rx *regexp.Regexp, err error) {
+	i := p.i
+	if len(p.s) < i+2 {
+		return nil, errors.New("expected regular expression, found EOF instead")
+	}
+
+	// number of open parens or brackets;
+	// when it becomes negative, finished parsing regex
+	open := 0
+
+loop:
+	for i < len(p.s) {
+		switch p.s[i] {
+		case '(', '[':
+			open++
+		case ')', ']':
+			open--
+			if open < 0 {
+				break loop
+			}
+		}
+		i++
+	}
+
+	if i >= len(p.s) {
+		return nil, errors.New("EOF in regular expression")
+	}
+	rx, err = regexp.Compile(p.s[p.i:i])
+	p.i = i
+	return rx, err
+}
+
+// skipWhitespace consumes whitespace characters and comments.
+// It returns true if there was actually anything to skip.
+func (p *parser) skipWhitespace() bool {
+	i := p.i
+	for i < len(p.s) {
+		switch p.s[i] {
+		case ' ', '\t', '\r', '\n', '\f':
+			i++
+			continue
+		case '/':
+			if strings.HasPrefix(p.s[i:], "/*") {
+				end := strings.Index(p.s[i+len("/*"):], "*/")
+				if end != -1 {
+					i += end + len("/**/")
+					continue
+				}
+			}
+		}
+		break
+	}
+
+	if i > p.i {
+		p.i = i
+		return true
+	}
+
+	return false
+}
+
+// consumeParenthesis consumes an opening parenthesis and any following
+// whitespace. It returns true if there was actually a parenthesis to skip.
+func (p *parser) consumeParenthesis() bool {
+	if p.i < len(p.s) && p.s[p.i] == '(' {
+		p.i++
+		p.skipWhitespace()
+		return true
+	}
+	return false
+}
+
+// consumeClosingParenthesis consumes a closing parenthesis and any preceding
+// whitespace. It returns true if there was actually a parenthesis to skip.
+func (p *parser) consumeClosingParenthesis() bool {
+	i := p.i
+	p.skipWhitespace()
+	if p.i < len(p.s) && p.s[p.i] == ')' {
+		p.i++
+		return true
+	}
+	p.i = i
+	return false
+}
+
+// parseTypeSelector parses a type selector (one that matches by tag name).
+func (p *parser) parseTypeSelector() (result Selector, err error) {
+	tag, err := p.parseIdentifier()
+	if err != nil {
+		return nil, err
+	}
+
+	return typeSelector(tag), nil
+}
+
+// parseIDSelector parses a selector that matches by id attribute.
+func (p *parser) parseIDSelector() (Selector, error) {
+	if p.i >= len(p.s) {
+		return nil, fmt.Errorf("expected id selector (#id), found EOF instead")
+	}
+	if p.s[p.i] != '#' {
+		return nil, fmt.Errorf("expected id selector (#id), found '%c' instead", p.s[p.i])
+	}
+
+	p.i++
+	id, err := p.parseName()
+	if err != nil {
+		return nil, err
+	}
+
+	return attributeEqualsSelector("id", id), nil
+}
+
+// parseClassSelector parses a selector that matches by class attribute.
+func (p *parser) parseClassSelector() (Selector, error) {
+	if p.i >= len(p.s) {
+		return nil, fmt.Errorf("expected class selector (.class), found EOF instead")
+	}
+	if p.s[p.i] != '.' {
+		return nil, fmt.Errorf("expected class selector (.class), found '%c' instead", p.s[p.i])
+	}
+
+	p.i++
+	class, err := p.parseIdentifier()
+	if err != nil {
+		return nil, err
+	}
+
+	return attributeIncludesSelector("class", class), nil
+}
+
+// parseAttributeSelector parses a selector that matches by attribute value.
+func (p *parser) parseAttributeSelector() (Selector, error) {
+	if p.i >= len(p.s) {
+		return nil, fmt.Errorf("expected attribute selector ([attribute]), found EOF instead")
+	}
+	if p.s[p.i] != '[' {
+		return nil, fmt.Errorf("expected attribute selector ([attribute]), found '%c' instead", p.s[p.i])
+	}
+
+	p.i++
+	p.skipWhitespace()
+	key, err := p.parseIdentifier()
+	if err != nil {
+		return nil, err
+	}
+
+	p.skipWhitespace()
+	if p.i >= len(p.s) {
+		return nil, errors.New("unexpected EOF in attribute selector")
+	}
+
+	if p.s[p.i] == ']' {
+		p.i++
+		return attributeExistsSelector(key), nil
+	}
+
+	if p.i+2 >= len(p.s) {
+		return nil, errors.New("unexpected EOF in attribute selector")
+	}
+
+	op := p.s[p.i : p.i+2]
+	if op[0] == '=' {
+		op = "="
+	} else if op[1] != '=' {
+		return nil, fmt.Errorf(`expected equality operator, found "%s" instead`, op)
+	}
+	p.i += len(op)
+
+	p.skipWhitespace()
+	if p.i >= len(p.s) {
+		return nil, errors.New("unexpected EOF in attribute selector")
+	}
+	var val string
+	var rx *regexp.Regexp
+	if op == "#=" {
+		rx, err = p.parseRegex()
+	} else {
+		switch p.s[p.i] {
+		case '\'', '"':
+			val, err = p.parseString()
+		default:
+			val, err = p.parseIdentifier()
+		}
+	}
+	if err != nil {
+		return nil, err
+	}
+
+	p.skipWhitespace()
+	if p.i >= len(p.s) {
+		return nil, errors.New("unexpected EOF in attribute selector")
+	}
+	if p.s[p.i] != ']' {
+		return nil, fmt.Errorf("expected ']', found '%c' instead", p.s[p.i])
+	}
+	p.i++
+
+	switch op {
+	case "=":
+		return attributeEqualsSelector(key, val), nil
+	case "~=":
+		return attributeIncludesSelector(key, val), nil
+	case "|=":
+		return attributeDashmatchSelector(key, val), nil
+	case "^=":
+		return attributePrefixSelector(key, val), nil
+	case "$=":
+		return attributeSuffixSelector(key, val), nil
+	case "*=":
+		return attributeSubstringSelector(key, val), nil
+	case "#=":
+		return attributeRegexSelector(key, rx), nil
+	}
+
+	return nil, fmt.Errorf("attribute operator %q is not supported", op)
+}
+
+var expectedParenthesis = errors.New("expected '(' but didn't find it")
+var expectedClosingParenthesis = errors.New("expected ')' but didn't find it")
+
+// parsePseudoclassSelector parses a pseudoclass selector like :not(p).
+func (p *parser) parsePseudoclassSelector() (Selector, error) {
+	if p.i >= len(p.s) {
+		return nil, fmt.Errorf("expected pseudoclass selector (:pseudoclass), found EOF instead")
+	}
+	if p.s[p.i] != ':' {
+		return nil, fmt.Errorf("expected attribute selector (:pseudoclass), found '%c' instead", p.s[p.i])
+	}
+
+	p.i++
+	name, err := p.parseIdentifier()
+	if err != nil {
+		return nil, err
+	}
+	name = toLowerASCII(name)
+
+	switch name {
+	case "not", "has", "haschild":
+		if !p.consumeParenthesis() {
+			return nil, expectedParenthesis
+		}
+		sel, err := p.parseSelectorGroup()
+		if err != nil {
+			return nil, err
+		}
+		if !p.consumeClosingParenthesis() {
+			return nil, expectedClosingParenthesis
+		}
+
+		switch name {
+		case "not":
+			return negatedSelector(sel), nil
+		case "has":
+			return hasDescendantSelector(sel), nil
+		case "haschild":
+			return hasChildSelector(sel), nil
+		}
+
+	case "contains", "containsown":
+		if !p.consumeParenthesis() {
+			return nil, expectedParenthesis
+		}
+		var val string
+		switch p.s[p.i] {
+		case '\'', '"':
+			val, err = p.parseString()
+		default:
+			val, err = p.parseIdentifier()
+		}
+		if err != nil {
+			return nil, err
+		}
+		val = strings.ToLower(val)
+		p.skipWhitespace()
+		if p.i >= len(p.s) {
+			return nil, errors.New("unexpected EOF in pseudo selector")
+		}
+		if !p.consumeClosingParenthesis() {
+			return nil, expectedClosingParenthesis
+		}
+
+		switch name {
+		case "contains":
+			return textSubstrSelector(val), nil
+		case "containsown":
+			return ownTextSubstrSelector(val), nil
+		}
+
+	case "matches", "matchesown":
+		if !p.consumeParenthesis() {
+			return nil, expectedParenthesis
+		}
+		rx, err := p.parseRegex()
+		if err != nil {
+			return nil, err
+		}
+		if p.i >= len(p.s) {
+			return nil, errors.New("unexpected EOF in pseudo selector")
+		}
+		if !p.consumeClosingParenthesis() {
+			return nil, expectedClosingParenthesis
+		}
+
+		switch name {
+		case "matches":
+			return textRegexSelector(rx), nil
+		case "matchesown":
+			return ownTextRegexSelector(rx), nil
+		}
+
+	case "nth-child", "nth-last-child", "nth-of-type", "nth-last-of-type":
+		if !p.consumeParenthesis() {
+			return nil, expectedParenthesis
+		}
+		a, b, err := p.parseNth()
+		if err != nil {
+			return nil, err
+		}
+		if !p.consumeClosingParenthesis() {
+			return nil, expectedClosingParenthesis
+		}
+		return nthChildSelector(a, b,
+				name == "nth-last-child" || name == "nth-last-of-type",
+				name == "nth-of-type" || name == "nth-last-of-type"),
+			nil
+
+	case "first-child":
+		return nthChildSelector(0, 1, false, false), nil
+	case "last-child":
+		return nthChildSelector(0, 1, true, false), nil
+	case "first-of-type":
+		return nthChildSelector(0, 1, false, true), nil
+	case "last-of-type":
+		return nthChildSelector(0, 1, true, true), nil
+	case "only-child":
+		return onlyChildSelector(false), nil
+	case "only-of-type":
+		return onlyChildSelector(true), nil
+	case "empty":
+		return emptyElementSelector, nil
+	}
+
+	return nil, fmt.Errorf("unknown pseudoclass :%s", name)
+}
+
+// parseInteger parses a  decimal integer.
+func (p *parser) parseInteger() (int, error) {
+	i := p.i
+	start := i
+	for i < len(p.s) && '0' <= p.s[i] && p.s[i] <= '9' {
+		i++
+	}
+	if i == start {
+		return 0, errors.New("expected integer, but didn't find it.")
+	}
+	p.i = i
+
+	val, err := strconv.Atoi(p.s[start:i])
+	if err != nil {
+		return 0, err
+	}
+
+	return val, nil
+}
+
+// parseNth parses the argument for :nth-child (normally of the form an+b).
+func (p *parser) parseNth() (a, b int, err error) {
+	// initial state
+	if p.i >= len(p.s) {
+		goto eof
+	}
+	switch p.s[p.i] {
+	case '-':
+		p.i++
+		goto negativeA
+	case '+':
+		p.i++
+		goto positiveA
+	case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+		goto positiveA
+	case 'n', 'N':
+		a = 1
+		p.i++
+		goto readN
+	case 'o', 'O', 'e', 'E':
+		id, err := p.parseName()
+		if err != nil {
+			return 0, 0, err
+		}
+		id = toLowerASCII(id)
+		if id == "odd" {
+			return 2, 1, nil
+		}
+		if id == "even" {
+			return 2, 0, nil
+		}
+		return 0, 0, fmt.Errorf("expected 'odd' or 'even', but found '%s' instead", id)
+	default:
+		goto invalid
+	}
+
+positiveA:
+	if p.i >= len(p.s) {
+		goto eof
+	}
+	switch p.s[p.i] {
+	case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+		a, err = p.parseInteger()
+		if err != nil {
+			return 0, 0, err
+		}
+		goto readA
+	case 'n', 'N':
+		a = 1
+		p.i++
+		goto readN
+	default:
+		goto invalid
+	}
+
+negativeA:
+	if p.i >= len(p.s) {
+		goto eof
+	}
+	switch p.s[p.i] {
+	case '0', '1', '2', '3', '4', '5', '6', '7', '8', '9':
+		a, err = p.parseInteger()
+		if err != nil {
+			return 0, 0, err
+		}
+		a = -a
+		goto readA
+	case 'n', 'N':
+		a = -1
+		p.i++
+		goto readN
+	default:
+		goto invalid
+	}
+
+readA:
+	if p.i >= len(p.s) {
+		goto eof
+	}
+	switch p.s[p.i] {
+	case 'n', 'N':
+		p.i++
+		goto readN
+	default:
+		// The number we read as a is actually b.
+		return 0, a, nil
+	}
+
+readN:
+	p.skipWhitespace()
+	if p.i >= len(p.s) {
+		goto eof
+	}
+	switch p.s[p.i] {
+	case '+':
+		p.i++
+		p.skipWhitespace()
+		b, err = p.parseInteger()
+		if err != nil {
+			return 0, 0, err
+		}
+		return a, b, nil
+	case '-':
+		p.i++
+		p.skipWhitespace()
+		b, err = p.parseInteger()
+		if err != nil {
+			return 0, 0, err
+		}
+		return a, -b, nil
+	default:
+		return a, 0, nil
+	}
+
+eof:
+	return 0, 0, errors.New("unexpected EOF while attempting to parse expression of form an+b")
+
+invalid:
+	return 0, 0, errors.New("unexpected character while attempting to parse expression of form an+b")
+}
+
+// parseSimpleSelectorSequence parses a selector sequence that applies to
+// a single element.
+func (p *parser) parseSimpleSelectorSequence() (Selector, error) {
+	var result Selector
+
+	if p.i >= len(p.s) {
+		return nil, errors.New("expected selector, found EOF instead")
+	}
+
+	switch p.s[p.i] {
+	case '*':
+		// It's the universal selector. Just skip over it, since it doesn't affect the meaning.
+		p.i++
+	case '#', '.', '[', ':':
+		// There's no type selector. Wait to process the other till the main loop.
+	default:
+		r, err := p.parseTypeSelector()
+		if err != nil {
+			return nil, err
+		}
+		result = r
+	}
+
+loop:
+	for p.i < len(p.s) {
+		var ns Selector
+		var err error
+		switch p.s[p.i] {
+		case '#':
+			ns, err = p.parseIDSelector()
+		case '.':
+			ns, err = p.parseClassSelector()
+		case '[':
+			ns, err = p.parseAttributeSelector()
+		case ':':
+			ns, err = p.parsePseudoclassSelector()
+		default:
+			break loop
+		}
+		if err != nil {
+			return nil, err
+		}
+		if result == nil {
+			result = ns
+		} else {
+			result = intersectionSelector(result, ns)
+		}
+	}
+
+	if result == nil {
+		result = func(n *html.Node) bool {
+			return true
+		}
+	}
+
+	return result, nil
+}
+
+// parseSelector parses a selector that may include combinators.
+func (p *parser) parseSelector() (result Selector, err error) {
+	p.skipWhitespace()
+	result, err = p.parseSimpleSelectorSequence()
+	if err != nil {
+		return
+	}
+
+	for {
+		var combinator byte
+		if p.skipWhitespace() {
+			combinator = ' '
+		}
+		if p.i >= len(p.s) {
+			return
+		}
+
+		switch p.s[p.i] {
+		case '+', '>', '~':
+			combinator = p.s[p.i]
+			p.i++
+			p.skipWhitespace()
+		case ',', ')':
+			// These characters can't begin a selector, but they can legally occur after one.
+			return
+		}
+
+		if combinator == 0 {
+			return
+		}
+
+		c, err := p.parseSimpleSelectorSequence()
+		if err != nil {
+			return nil, err
+		}
+
+		switch combinator {
+		case ' ':
+			result = descendantSelector(result, c)
+		case '>':
+			result = childSelector(result, c)
+		case '+':
+			result = siblingSelector(result, c, true)
+		case '~':
+			result = siblingSelector(result, c, false)
+		}
+	}
+
+	panic("unreachable")
+}
+
+// parseSelectorGroup parses a group of selectors, separated by commas.
+func (p *parser) parseSelectorGroup() (result Selector, err error) {
+	result, err = p.parseSelector()
+	if err != nil {
+		return
+	}
+
+	for p.i < len(p.s) {
+		if p.s[p.i] != ',' {
+			return result, nil
+		}
+		p.i++
+		c, err := p.parseSelector()
+		if err != nil {
+			return nil, err
+		}
+		result = unionSelector(result, c)
+	}
+
+	return
+}

vendor/code.google.com/p/cascadia/selector.go

@@ -0,0 +1,487 @@
+package cascadia
+
+import (
+	"bytes"
+	"code.google.com/p/go.net/html"
+	"fmt"
+	"regexp"
+	"strings"
+)
+
+// the Selector type, and functions for creating them
+
+// A Selector is a function which tells whether a node matches or not.
+type Selector func(*html.Node) bool
+
+// hasChildMatch returns whether n has any child that matches a.
+func hasChildMatch(n *html.Node, a Selector) bool {
+	for c := n.FirstChild; c != nil; c = c.NextSibling {
+		if a(c) {
+			return true
+		}
+	}
+	return false
+}
+
+// hasDescendantMatch performs a depth-first search of n's descendants,
+// testing whether any of them match a. It returns true as soon as a match is
+// found, or false if no match is found.
+func hasDescendantMatch(n *html.Node, a Selector) bool {
+	for c := n.FirstChild; c != nil; c = c.NextSibling {
+		if a(c) || (c.Type == html.ElementNode && hasDescendantMatch(c, a)) {
+			return true
+		}
+	}
+	return false
+}
+
+// Compile parses a selector and returns, if successful, a Selector object
+// that can be used to match against html.Node objects.
+func Compile(sel string) (Selector, error) {
+	p := &parser{s: sel}
+	compiled, err := p.parseSelectorGroup()
+	if err != nil {
+		return nil, err
+	}
+
+	if p.i < len(sel) {
+		return nil, fmt.Errorf("parsing %q: %d bytes left over", sel, len(sel)-p.i)
+	}
+
+	return compiled, nil
+}
+
+// MustCompile is like Compile, but panics instead of returning an error.
+func MustCompile(sel string) Selector {
+	compiled, err := Compile(sel)
+	if err != nil {
+		panic(err)
+	}
+	return compiled
+}
+
+// MatchAll returns a slice of the nodes that match the selector,
+// from n and its children.
+func (s Selector) MatchAll(n *html.Node) []*html.Node {
+	return s.matchAllInto(n, nil)
+}
+
+func (s Selector) matchAllInto(n *html.Node, storage []*html.Node) []*html.Node {
+	if s(n) {
+		storage = append(storage, n)
+	}
+
+	for child := n.FirstChild; child != nil; child = child.NextSibling {
+		storage = s.matchAllInto(child, storage)
+	}
+
+	return storage
+}
+
+// Match returns true if the node matches the selector.
+func (s Selector) Match(n *html.Node) bool {
+	return s(n)
+}
+
+// Filter returns the nodes in nodes that match the selector.
+func (s Selector) Filter(nodes []*html.Node) (result []*html.Node) {
+	for _, n := range nodes {
+		if s(n) {
+			result = append(result, n)
+		}
+	}
+	return result
+}
+
+// typeSelector returns a Selector that matches elements with a given tag name.
+func typeSelector(tag string) Selector {
+	tag = toLowerASCII(tag)
+	return func(n *html.Node) bool {
+		return n.Type == html.ElementNode && n.Data == tag
+	}
+}
+
+// toLowerASCII returns s with all ASCII capital letters lowercased.
+func toLowerASCII(s string) string {
+	var b []byte
+	for i := 0; i < len(s); i++ {
+		if c := s[i]; 'A' <= c && c <= 'Z' {
+			if b == nil {
+				b = make([]byte, len(s))
+				copy(b, s)
+			}
+			b[i] = s[i] + ('a' - 'A')
+		}
+	}
+
+	if b == nil {
+		return s
+	}
+
+	return string(b)
+}
+
+// attributeSelector returns a Selector that matches elements
+// where the attribute named key satisifes the function f.
+func attributeSelector(key string, f func(string) bool) Selector {
+	key = toLowerASCII(key)
+	return func(n *html.Node) bool {
+		if n.Type != html.ElementNode {
+			return false
+		}
+		for _, a := range n.Attr {
+			if a.Key == key && f(a.Val) {
+				return true
+			}
+		}
+		return false
+	}
+}
+
+// attributeExistsSelector returns a Selector that matches elements that have
+// an attribute named key.
+func attributeExistsSelector(key string) Selector {
+	return attributeSelector(key, func(string) bool { return true })
+}
+
+// attributeEqualsSelector returns a Selector that matches elements where
+// the attribute named key has the value val.
+func attributeEqualsSelector(key, val string) Selector {
+	return attributeSelector(key,
+		func(s string) bool {
+			return s == val
+		})
+}
+
+// attributeIncludesSelector returns a Selector that matches elements where
+// the attribute named key is a whitespace-separated list that includes val.
+func attributeIncludesSelector(key, val string) Selector {
+	return attributeSelector(key,
+		func(s string) bool {
+			for s != "" {
+				i := strings.IndexAny(s, " \t\r\n\f")
+				if i == -1 {
+					return s == val
+				}
+				if s[:i] == val {
+					return true
+				}
+				s = s[i+1:]
+			}
+			return false
+		})
+}
+
+// attributeDashmatchSelector returns a Selector that matches elements where
+// the attribute named key equals val or starts with val plus a hyphen.
+func attributeDashmatchSelector(key, val string) Selector {
+	return attributeSelector(key,
+		func(s string) bool {
+			if s == val {
+				return true
+			}
+			if len(s) <= len(val) {
+				return false
+			}
+			if s[:len(val)] == val && s[len(val)] == '-' {
+				return true
+			}
+			return false
+		})
+}
+
+// attributePrefixSelector returns a Selector that matches elements where
+// the attribute named key starts with val.
+func attributePrefixSelector(key, val string) Selector {
+	return attributeSelector(key,
+		func(s string) bool {
+			return strings.HasPrefix(s, val)
+		})
+}
+
+// attributeSuffixSelector returns a Selector that matches elements where
+// the attribute named key ends with val.
+func attributeSuffixSelector(key, val string) Selector {
+	return attributeSelector(key,
+		func(s string) bool {
+			return strings.HasSuffix(s, val)
+		})
+}
+
+// attributeSubstringSelector returns a Selector that matches nodes where
+// the attribute named key contains val.
+func attributeSubstringSelector(key, val string) Selector {
+	return attributeSelector(key,
+		func(s string) bool {
+			return strings.Contains(s, val)
+		})
+}
+
+// attributeRegexSelector returns a Selector that matches nodes where
+// the attribute named key matches the regular expression rx
+func attributeRegexSelector(key string, rx *regexp.Regexp) Selector {
+	return attributeSelector(key,
+		func(s string) bool {
+			return rx.MatchString(s)
+		})
+}
+
+// intersectionSelector returns a selector that matches nodes that match
+// both a and b.
+func intersectionSelector(a, b Selector) Selector {
+	return func(n *html.Node) bool {
+		return a(n) && b(n)
+	}
+}
+
+// unionSelector returns a selector that matches elements that match
+// either a or b.
+func unionSelector(a, b Selector) Selector {
+	return func(n *html.Node) bool {
+		return a(n) || b(n)
+	}
+}
+
+// negatedSelector returns a selector that matches elements that do not match a.
+func negatedSelector(a Selector) Selector {
+	return func(n *html.Node) bool {
+		if n.Type != html.ElementNode {
+			return false
+		}
+		return !a(n)
+	}
+}
+
+// writeNodeText writes the text contained in n and its descendants to b.
+func writeNodeText(n *html.Node, b *bytes.Buffer) {
+	switch n.Type {
+	case html.TextNode:
+		b.WriteString(n.Data)
+	case html.ElementNode:
+		for c := n.FirstChild; c != nil; c = c.NextSibling {
+			writeNodeText(c, b)
+		}
+	}
+}
+
+// nodeText returns the text contained in n and its descendants.
+func nodeText(n *html.Node) string {
+	var b bytes.Buffer
+	writeNodeText(n, &b)
+	return b.String()
+}
+
+// nodeOwnText returns the contents of the text nodes that are direct
+// children of n.
+func nodeOwnText(n *html.Node) string {
+	var b bytes.Buffer
+	for c := n.FirstChild; c != nil; c = c.NextSibling {
+		if c.Type == html.TextNode {
+			b.WriteString(c.Data)
+		}
+	}
+	return b.String()
+}
+
+// textSubstrSelector returns a selector that matches nodes that
+// contain the given text.
+func textSubstrSelector(val string) Selector {
+	return func(n *html.Node) bool {
+		text := strings.ToLower(nodeText(n))
+		return strings.Contains(text, val)
+	}
+}
+
+// ownTextSubstrSelector returns a selector that matches nodes that
+// directly contain the given text
+func ownTextSubstrSelector(val string) Selector {
+	return func(n *html.Node) bool {
+		text := strings.ToLower(nodeOwnText(n))
+		return strings.Contains(text, val)
+	}
+}
+
+// textRegexSelector returns a selector that matches nodes whose text matches
+// the specified regular expression
+func textRegexSelector(rx *regexp.Regexp) Selector {
+	return func(n *html.Node) bool {
+		return rx.MatchString(nodeText(n))
+	}
+}
+
+// ownTextRegexSelector returns a selector that matches nodes whose text
+// directly matches the specified regular expression
+func ownTextRegexSelector(rx *regexp.Regexp) Selector {
+	return func(n *html.Node) bool {
+		return rx.MatchString(nodeOwnText(n))
+	}
+}
+
+// hasChildSelector returns a selector that matches elements
+// with a child that matches a.
+func hasChildSelector(a Selector) Selector {
+	return func(n *html.Node) bool {
+		if n.Type != html.ElementNode {
+			return false
+		}
+		return hasChildMatch(n, a)
+	}
+}
+
+// hasDescendantSelector returns a selector that matches elements
+// with any descendant that matches a.
+func hasDescendantSelector(a Selector) Selector {
+	return func(n *html.Node) bool {
+		if n.Type != html.ElementNode {
+			return false
+		}
+		return hasDescendantMatch(n, a)
+	}
+}
+
+// nthChildSelector returns a selector that implements :nth-child(an+b).
+// If last is true, implements :nth-last-child instead.
+// If ofType is true, implements :nth-of-type instead.
+func nthChildSelector(a, b int, last, ofType bool) Selector {
+	return func(n *html.Node) bool {
+		if n.Type != html.ElementNode {
+			return false
+		}
+
+		parent := n.Parent
+		if parent == nil {
+			return false
+		}
+
+		i := -1
+		count := 0
+		for c := parent.FirstChild; c != nil; c = c.NextSibling {
+			if (c.Type != html.ElementNode) || (ofType && c.Data != n.Data) {
+				continue
+			}
+			count++
+			if c == n {
+				i = count
+				if !last {
+					break
+				}
+			}
+		}
+
+		if i == -1 {
+			// This shouldn't happen, since n should always be one of its parent's children.
+			return false
+		}
+
+		if last {
+			i = count - i + 1
+		}
+
+		i -= b
+		if a == 0 {
+			return i == 0
+		}
+
+		return i%a == 0 && i/a >= 0
+	}
+}
+
+// onlyChildSelector returns a selector that implements :only-child.
+// If ofType is true, it implements :only-of-type instead.
+func onlyChildSelector(ofType bool) Selector {
+	return func(n *html.Node) bool {
+		if n.Type != html.ElementNode {
+			return false
+		}
+
+		parent := n.Parent
+		if parent == nil {
+			return false
+		}
+
+		count := 0
+		for c := parent.FirstChild; c != nil; c = c.NextSibling {
+			if (c.Type != html.ElementNode) || (ofType && c.Data != n.Data) {
+				continue
+			}
+			count++
+			if count > 1 {
+				return false
+			}
+		}
+
+		return count == 1
+	}
+}
+
+// emptyElementSelector is a Selector that matches empty elements.
+func emptyElementSelector(n *html.Node) bool {
+	if n.Type != html.ElementNode {
+		return false
+	}
+
+	for c := n.FirstChild; c != nil; c = c.NextSibling {
+		switch c.Type {
+		case html.ElementNode, html.TextNode:
+			return false
+		}
+	}
+
+	return true
+}
+
+// descendantSelector returns a Selector that matches an element if
+// it matches d and has an ancestor that matches a.
+func descendantSelector(a, d Selector) Selector {
+	return func(n *html.Node) bool {
+		if !d(n) {
+			return false
+		}
+
+		for p := n.Parent; p != nil; p = p.Parent {
+			if a(p) {
+				return true
+			}
+		}
+
+		return false
+	}
+}
+
+// childSelector returns a Selector that matches an element if
+// it matches d and its parent matches a.
+func childSelector(a, d Selector) Selector {
+	return func(n *html.Node) bool {
+		return d(n) && n.Parent != nil && a(n.Parent)
+	}
+}
+
+// siblingSelector returns a Selector that matches an element
+// if it matches s2 and in is preceded by an element that matches s1.
+// If adjacent is true, the sibling must be immediately before the element.
+func siblingSelector(s1, s2 Selector, adjacent bool) Selector {
+	return func(n *html.Node) bool {
+		if !s2(n) {
+			return false
+		}
+
+		if adjacent {
+			for n = n.PrevSibling; n != nil; n = n.PrevSibling {
+				if n.Type == html.TextNode || n.Type == html.CommentNode {
+					continue
+				}
+				return s1(n)
+			}
+			return false
+		}
+
+		// Walk backwards looking for element that matches s1
+		for c := n.PrevSibling; c != nil; c = c.PrevSibling {
+			if s1(c) {
+				return true
+			}
+		}
+
+		return false
+	}
+}