vendor: adding deps

Signed-off-by: Vincent Batts <vbatts@hashbangbash.com>

vendor/github.com/andybalholm/cascadia/.travis.yml

@@ -0,0 +1,14 @@
+language: go
+
+go:
+  - 1.3
+  - 1.4
+
+install:
+  - go get github.com/andybalholm/cascadia
+
+script:
+ - go test -v
+
+notifications:
+  email: false

vendor/github.com/andybalholm/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/github.com/andybalholm/cascadia/README.md

@@ -0,0 +1,9 @@
+# cascadia
+
+[![](https://travis-ci.org/andybalholm/cascadia.svg)](https://travis-ci.org/andybalholm/cascadia)
+
+The Cascadia package implements CSS selectors for use with the parse trees produced by the html package.
+
+To test CSS selectors without writing Go code, check out [cascadia](https://github.com/suntong/cascadia) the command line tool, a thin wrapper around this package.
+
+[Refer to godoc here](https://godoc.org/github.com/andybalholm/cascadia).

vendor/github.com/andybalholm/cascadia/go.mod

@@ -0,0 +1,3 @@
+module "github.com/andybalholm/cascadia"
+
+require "golang.org/x/net" v0.0.0-20180218175443-cbe0f9307d01

vendor/github.com/andybalholm/cascadia/parser.go

@@ -0,0 +1,801 @@
+// Package cascadia is an implementation of CSS selectors.
+package cascadia
+
+import (
+	"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
+}
+
+// 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)
+}
+
+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 tagSelector, err error) {
+	tag, err := p.parseIdentifier()
+	if err != nil {
+		return
+	}
+	return tagSelector{tag: toLowerASCII(tag)}, nil
+}
+
+// parseIDSelector parses a selector that matches by id attribute.
+func (p *parser) parseIDSelector() (idSelector, error) {
+	if p.i >= len(p.s) {
+		return idSelector{}, fmt.Errorf("expected id selector (#id), found EOF instead")
+	}
+	if p.s[p.i] != '#' {
+		return idSelector{}, fmt.Errorf("expected id selector (#id), found '%c' instead", p.s[p.i])
+	}
+
+	p.i++
+	id, err := p.parseName()
+	if err != nil {
+		return idSelector{}, err
+	}
+
+	return idSelector{id: id}, nil
+}
+
+// parseClassSelector parses a selector that matches by class attribute.
+func (p *parser) parseClassSelector() (classSelector, error) {
+	if p.i >= len(p.s) {
+		return classSelector{}, fmt.Errorf("expected class selector (.class), found EOF instead")
+	}
+	if p.s[p.i] != '.' {
+		return classSelector{}, fmt.Errorf("expected class selector (.class), found '%c' instead", p.s[p.i])
+	}
+
+	p.i++
+	class, err := p.parseIdentifier()
+	if err != nil {
+		return classSelector{}, err
+	}
+
+	return classSelector{class: class}, nil
+}
+
+// parseAttributeSelector parses a selector that matches by attribute value.
+func (p *parser) parseAttributeSelector() (attrSelector, error) {
+	if p.i >= len(p.s) {
+		return attrSelector{}, fmt.Errorf("expected attribute selector ([attribute]), found EOF instead")
+	}
+	if p.s[p.i] != '[' {
+		return attrSelector{}, 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 attrSelector{}, err
+	}
+	key = toLowerASCII(key)
+
+	p.skipWhitespace()
+	if p.i >= len(p.s) {
+		return attrSelector{}, errors.New("unexpected EOF in attribute selector")
+	}
+
+	if p.s[p.i] == ']' {
+		p.i++
+		return attrSelector{key: key, operation: ""}, nil
+	}
+
+	if p.i+2 >= len(p.s) {
+		return attrSelector{}, errors.New("unexpected EOF in attribute selector")
+	}
+
+	op := p.s[p.i : p.i+2]
+	if op[0] == '=' {
+		op = "="
+	} else if op[1] != '=' {
+		return attrSelector{}, fmt.Errorf(`expected equality operator, found "%s" instead`, op)
+	}
+	p.i += len(op)
+
+	p.skipWhitespace()
+	if p.i >= len(p.s) {
+		return attrSelector{}, 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 attrSelector{}, err
+	}
+
+	p.skipWhitespace()
+	if p.i >= len(p.s) {
+		return attrSelector{}, errors.New("unexpected EOF in attribute selector")
+	}
+	if p.s[p.i] != ']' {
+		return attrSelector{}, fmt.Errorf("expected ']', found '%c' instead", p.s[p.i])
+	}
+	p.i++
+
+	switch op {
+	case "=", "!=", "~=", "|=", "^=", "$=", "*=", "#=":
+		return attrSelector{key: key, val: val, operation: op, regexp: rx}, nil
+	default:
+		return attrSelector{}, fmt.Errorf("attribute operator %q is not supported", op)
+	}
+}
+
+var errExpectedParenthesis = errors.New("expected '(' but didn't find it")
+var errExpectedClosingParenthesis = errors.New("expected ')' but didn't find it")
+var errUnmatchedParenthesis = errors.New("unmatched '('")
+
+// parsePseudoclassSelector parses a pseudoclass selector like :not(p)
+func (p *parser) parsePseudoclassSelector() (out Sel, err 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++
+	if p.s[p.i] == ':' { // we found a pseudo-element
+		p.i++
+	}
+
+	name, err := p.parseIdentifier()
+	if err != nil {
+		return
+	}
+	name = toLowerASCII(name)
+	switch name {
+	case "not", "has", "haschild":
+		if !p.consumeParenthesis() {
+			return out, errExpectedParenthesis
+		}
+		sel, parseErr := p.parseSelectorGroup()
+		if parseErr != nil {
+			return out, parseErr
+		}
+		if !p.consumeClosingParenthesis() {
+			return out, errExpectedClosingParenthesis
+		}
+
+		out = relativePseudoClassSelector{name: name, match: sel}
+
+	case "contains", "containsown":
+		if !p.consumeParenthesis() {
+			return out, errExpectedParenthesis
+		}
+		if p.i == len(p.s) {
+			return out, errUnmatchedParenthesis
+		}
+		var val string
+		switch p.s[p.i] {
+		case '\'', '"':
+			val, err = p.parseString()
+		default:
+			val, err = p.parseIdentifier()
+		}
+		if err != nil {
+			return out, err
+		}
+		val = strings.ToLower(val)
+		p.skipWhitespace()
+		if p.i >= len(p.s) {
+			return out, errors.New("unexpected EOF in pseudo selector")
+		}
+		if !p.consumeClosingParenthesis() {
+			return out, errExpectedClosingParenthesis
+		}
+
+		out = containsPseudoClassSelector{own: name == "containsown", value: val}
+
+	case "matches", "matchesown":
+		if !p.consumeParenthesis() {
+			return out, errExpectedParenthesis
+		}
+		rx, err := p.parseRegex()
+		if err != nil {
+			return out, err
+		}
+		if p.i >= len(p.s) {
+			return out, errors.New("unexpected EOF in pseudo selector")
+		}
+		if !p.consumeClosingParenthesis() {
+			return out, errExpectedClosingParenthesis
+		}
+
+		out = regexpPseudoClassSelector{own: name == "matchesown", regexp: rx}
+
+	case "nth-child", "nth-last-child", "nth-of-type", "nth-last-of-type":
+		if !p.consumeParenthesis() {
+			return out, errExpectedParenthesis
+		}
+		a, b, err := p.parseNth()
+		if err != nil {
+			return out, err
+		}
+		if !p.consumeClosingParenthesis() {
+			return out, errExpectedClosingParenthesis
+		}
+		last := name == "nth-last-child" || name == "nth-last-of-type"
+		ofType := name == "nth-of-type" || name == "nth-last-of-type"
+		out = nthPseudoClassSelector{a: a, b: b, last: last, ofType: ofType}
+
+	case "first-child":
+		out = nthPseudoClassSelector{a: 0, b: 1, ofType: false, last: false}
+	case "last-child":
+		out = nthPseudoClassSelector{a: 0, b: 1, ofType: false, last: true}
+	case "first-of-type":
+		out = nthPseudoClassSelector{a: 0, b: 1, ofType: true, last: false}
+	case "last-of-type":
+		out = nthPseudoClassSelector{a: 0, b: 1, ofType: true, last: true}
+	case "only-child":
+		out = onlyChildPseudoClassSelector{ofType: false}
+	case "only-of-type":
+		out = onlyChildPseudoClassSelector{ofType: true}
+	case "input":
+		out = inputPseudoClassSelector{}
+	case "empty":
+		out = emptyElementPseudoClassSelector{}
+	case "root":
+		out = rootPseudoClassSelector{}
+	case "after", "backdrop", "before", "cue", "first-letter", "first-line", "grammar-error", "marker", "placeholder", "selection", "spelling-error":
+		return out, errors.New("pseudo-elements are not yet supported")
+	default:
+		return out, fmt.Errorf("unknown pseudoclass or pseudoelement :%s", name)
+	}
+	return
+}
+
+// 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, nameErr := p.parseName()
+		if nameErr != nil {
+			return 0, 0, nameErr
+		}
+		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() (Sel, error) {
+	var selectors []Sel
+
+	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
+		}
+		selectors = append(selectors, r)
+	}
+
+loop:
+	for p.i < len(p.s) {
+		var (
+			ns  Sel
+			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
+		}
+
+		selectors = append(selectors, ns)
+	}
+	if len(selectors) == 1 { // no need wrap the selectors in compoundSelector
+		return selectors[0], nil
+	}
+	return compoundSelector{selectors: selectors}, nil
+}
+
+// parseSelector parses a selector that may include combinators.
+func (p *parser) parseSelector() (Sel, error) {
+	p.skipWhitespace()
+	result, err := p.parseSimpleSelectorSequence()
+	if err != nil {
+		return nil, err
+	}
+
+	for {
+		var (
+			combinator byte
+			c          Sel
+		)
+		if p.skipWhitespace() {
+			combinator = ' '
+		}
+		if p.i >= len(p.s) {
+			return result, nil
+		}
+
+		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 result, nil
+		}
+
+		if combinator == 0 {
+			return result, nil
+		}
+
+		c, err = p.parseSimpleSelectorSequence()
+		if err != nil {
+			return nil, err
+		}
+		result = combinedSelector{first: result, combinator: combinator, second: c}
+	}
+}
+
+// parseSelectorGroup parses a group of selectors, separated by commas.
+func (p *parser) parseSelectorGroup() (SelectorGroup, error) {
+	current, err := p.parseSelector()
+	if err != nil {
+		return nil, err
+	}
+	result := SelectorGroup{current}
+
+	for p.i < len(p.s) {
+		if p.s[p.i] != ',' {
+			break
+		}
+		p.i++
+		c, err := p.parseSelector()
+		if err != nil {
+			return nil, err
+		}
+		result = append(result, c)
+	}
+	return result, nil
+}

vendor/github.com/andybalholm/cascadia/selector.go

@@ -0,0 +1,833 @@
+package cascadia
+
+import (
+	"bytes"
+	"fmt"
+	"regexp"
+	"strings"
+
+	"golang.org/x/net/html"
+)
+
+// Matcher is the interface for basic selector functionality.
+// Match returns whether a selector matches n.
+type Matcher interface {
+	Match(n *html.Node) bool
+}
+
+// Sel is the interface for all the functionality provided by selectors.
+// It is currently the same as Matcher, but other methods may be added in the
+// future.
+type Sel interface {
+	Matcher
+	Specificity() Specificity
+}
+
+// Parse parses a selector.
+func Parse(sel string) (Sel, error) {
+	p := &parser{s: sel}
+	compiled, err := p.parseSelector()
+	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
+}
+
+// ParseGroup parses a selector, or a group of selectors separated by commas.
+func ParseGroup(sel string) (SelectorGroup, 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
+}
+
+// A Selector is a function which tells whether a node matches or not.
+//
+// This type is maintained for compatibility; I recommend using the newer and
+// more idiomatic interfaces Sel and Matcher.
+type Selector func(*html.Node) bool
+
+// 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) {
+	compiled, err := ParseGroup(sel)
+	if err != nil {
+		return nil, err
+	}
+
+	return Selector(compiled.Match), 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
+}
+
+func queryInto(n *html.Node, m Matcher, storage []*html.Node) []*html.Node {
+	for child := n.FirstChild; child != nil; child = child.NextSibling {
+		if m.Match(child) {
+			storage = append(storage, child)
+		}
+		storage = queryInto(child, m, storage)
+	}
+
+	return storage
+}
+
+// QueryAll returns a slice of all the nodes that match m, from the descendants
+// of n.
+func QueryAll(n *html.Node, m Matcher) []*html.Node {
+	return queryInto(n, m, nil)
+}
+
+// Match returns true if the node matches the selector.
+func (s Selector) Match(n *html.Node) bool {
+	return s(n)
+}
+
+// MatchFirst returns the first node that matches s, from n and its children.
+func (s Selector) MatchFirst(n *html.Node) *html.Node {
+	if s.Match(n) {
+		return n
+	}
+
+	for c := n.FirstChild; c != nil; c = c.NextSibling {
+		m := s.MatchFirst(c)
+		if m != nil {
+			return m
+		}
+	}
+	return nil
+}
+
+// Query returns the first node that matches m, from the descendants of n.
+// If none matches, it returns nil.
+func Query(n *html.Node, m Matcher) *html.Node {
+	for c := n.FirstChild; c != nil; c = c.NextSibling {
+		if m.Match(c) {
+			return c
+		}
+		if matched := Query(c, m); matched != nil {
+			return matched
+		}
+	}
+
+	return nil
+}
+
+// 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
+}
+
+// Filter returns the nodes that match m.
+func Filter(nodes []*html.Node, m Matcher) (result []*html.Node) {
+	for _, n := range nodes {
+		if m.Match(n) {
+			result = append(result, n)
+		}
+	}
+	return result
+}
+
+type tagSelector struct {
+	tag string
+}
+
+// Matches elements with a given tag name.
+func (t tagSelector) Match(n *html.Node) bool {
+	return n.Type == html.ElementNode && n.Data == t.tag
+}
+
+func (c tagSelector) Specificity() Specificity {
+	return Specificity{0, 0, 1}
+}
+
+type classSelector struct {
+	class string
+}
+
+// Matches elements by class attribute.
+func (t classSelector) Match(n *html.Node) bool {
+	return matchAttribute(n, "class", func(s string) bool {
+		return matchInclude(t.class, s)
+	})
+}
+
+func (c classSelector) Specificity() Specificity {
+	return Specificity{0, 1, 0}
+}
+
+type idSelector struct {
+	id string
+}
+
+// Matches elements by id attribute.
+func (t idSelector) Match(n *html.Node) bool {
+	return matchAttribute(n, "id", func(s string) bool {
+		return s == t.id
+	})
+}
+
+func (c idSelector) Specificity() Specificity {
+	return Specificity{1, 0, 0}
+}
+
+type attrSelector struct {
+	key, val, operation string
+	regexp              *regexp.Regexp
+}
+
+// Matches elements by attribute value.
+func (t attrSelector) Match(n *html.Node) bool {
+	switch t.operation {
+	case "":
+		return matchAttribute(n, t.key, func(string) bool { return true })
+	case "=":
+		return matchAttribute(n, t.key, func(s string) bool { return s == t.val })
+	case "!=":
+		return attributeNotEqualMatch(t.key, t.val, n)
+	case "~=":
+		// matches elements where the attribute named key is a whitespace-separated list that includes val.
+		return matchAttribute(n, t.key, func(s string) bool { return matchInclude(t.val, s) })
+	case "|=":
+		return attributeDashMatch(t.key, t.val, n)
+	case "^=":
+		return attributePrefixMatch(t.key, t.val, n)
+	case "$=":
+		return attributeSuffixMatch(t.key, t.val, n)
+	case "*=":
+		return attributeSubstringMatch(t.key, t.val, n)
+	case "#=":
+		return attributeRegexMatch(t.key, t.regexp, n)
+	default:
+		panic(fmt.Sprintf("unsuported operation : %s", t.operation))
+	}
+}
+
+// matches elements where the attribute named key satisifes the function f.
+func matchAttribute(n *html.Node, key string, f func(string) bool) bool {
+	if n.Type != html.ElementNode {
+		return false
+	}
+	for _, a := range n.Attr {
+		if a.Key == key && f(a.Val) {
+			return true
+		}
+	}
+	return false
+}
+
+// attributeNotEqualMatch matches elements where
+// the attribute named key does not have the value val.
+func attributeNotEqualMatch(key, val string, n *html.Node) bool {
+	if n.Type != html.ElementNode {
+		return false
+	}
+	for _, a := range n.Attr {
+		if a.Key == key && a.Val == val {
+			return false
+		}
+	}
+	return true
+}
+
+// returns true if s is a whitespace-separated list that includes val.
+func matchInclude(val, 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
+}
+
+//  matches elements where the attribute named key equals val or starts with val plus a hyphen.
+func attributeDashMatch(key, val string, n *html.Node) bool {
+	return matchAttribute(n, 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
+		})
+}
+
+// attributePrefixMatch returns a Selector that matches elements where
+// the attribute named key starts with val.
+func attributePrefixMatch(key, val string, n *html.Node) bool {
+	return matchAttribute(n, key,
+		func(s string) bool {
+			if strings.TrimSpace(s) == "" {
+				return false
+			}
+			return strings.HasPrefix(s, val)
+		})
+}
+
+// attributeSuffixMatch matches elements where
+// the attribute named key ends with val.
+func attributeSuffixMatch(key, val string, n *html.Node) bool {
+	return matchAttribute(n, key,
+		func(s string) bool {
+			if strings.TrimSpace(s) == "" {
+				return false
+			}
+			return strings.HasSuffix(s, val)
+		})
+}
+
+// attributeSubstringMatch matches nodes where
+// the attribute named key contains val.
+func attributeSubstringMatch(key, val string, n *html.Node) bool {
+	return matchAttribute(n, key,
+		func(s string) bool {
+			if strings.TrimSpace(s) == "" {
+				return false
+			}
+			return strings.Contains(s, val)
+		})
+}
+
+// attributeRegexMatch  matches nodes where
+// the attribute named key matches the regular expression rx
+func attributeRegexMatch(key string, rx *regexp.Regexp, n *html.Node) bool {
+	return matchAttribute(n, key,
+		func(s string) bool {
+			return rx.MatchString(s)
+		})
+}
+
+func (c attrSelector) Specificity() Specificity {
+	return Specificity{0, 1, 0}
+}
+
+// ---------------- Pseudo class selectors ----------------
+// we use severals concrete types of pseudo-class selectors
+
+type relativePseudoClassSelector struct {
+	name  string // one of "not", "has", "haschild"
+	match SelectorGroup
+}
+
+func (s relativePseudoClassSelector) Match(n *html.Node) bool {
+	if n.Type != html.ElementNode {
+		return false
+	}
+	switch s.name {
+	case "not":
+		// matches elements that do not match a.
+		return !s.match.Match(n)
+	case "has":
+		//  matches elements with any descendant that matches a.
+		return hasDescendantMatch(n, s.match)
+	case "haschild":
+		// matches elements with a child that matches a.
+		return hasChildMatch(n, s.match)
+	default:
+		panic(fmt.Sprintf("unsupported relative pseudo class selector : %s", s.name))
+	}
+}
+
+// hasChildMatch returns whether n has any child that matches a.
+func hasChildMatch(n *html.Node, a Matcher) bool {
+	for c := n.FirstChild; c != nil; c = c.NextSibling {
+		if a.Match(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 Matcher) bool {
+	for c := n.FirstChild; c != nil; c = c.NextSibling {
+		if a.Match(c) || (c.Type == html.ElementNode && hasDescendantMatch(c, a)) {
+			return true
+		}
+	}
+	return false
+}
+
+// Specificity returns the specificity of the most specific selectors
+// in the pseudo-class arguments.
+// See https://www.w3.org/TR/selectors/#specificity-rules
+func (s relativePseudoClassSelector) Specificity() Specificity {
+	var max Specificity
+	for _, sel := range s.match {
+		newSpe := sel.Specificity()
+		if max.Less(newSpe) {
+			max = newSpe
+		}
+	}
+	return max
+}
+
+type containsPseudoClassSelector struct {
+	own   bool
+	value string
+}
+
+func (s containsPseudoClassSelector) Match(n *html.Node) bool {
+	var text string
+	if s.own {
+		// matches nodes that directly contain the given text
+		text = strings.ToLower(nodeOwnText(n))
+	} else {
+		// matches nodes that contain the given text.
+		text = strings.ToLower(nodeText(n))
+	}
+	return strings.Contains(text, s.value)
+}
+
+func (s containsPseudoClassSelector) Specificity() Specificity {
+	return Specificity{0, 1, 0}
+}
+
+type regexpPseudoClassSelector struct {
+	own    bool
+	regexp *regexp.Regexp
+}
+
+func (s regexpPseudoClassSelector) Match(n *html.Node) bool {
+	var text string
+	if s.own {
+		// matches nodes whose text directly matches the specified regular expression
+		text = nodeOwnText(n)
+	} else {
+		// matches nodes whose text matches the specified regular expression
+		text = nodeText(n)
+	}
+	return s.regexp.MatchString(text)
+}
+
+// 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()
+}
+
+func (s regexpPseudoClassSelector) Specificity() Specificity {
+	return Specificity{0, 1, 0}
+}
+
+type nthPseudoClassSelector struct {
+	a, b         int
+	last, ofType bool
+}
+
+func (s nthPseudoClassSelector) Match(n *html.Node) bool {
+	if s.a == 0 {
+		if s.last {
+			return simpleNthLastChildMatch(s.b, s.ofType, n)
+		} else {
+			return simpleNthChildMatch(s.b, s.ofType, n)
+		}
+	}
+	return nthChildMatch(s.a, s.b, s.last, s.ofType, n)
+}
+
+// nthChildMatch implements :nth-child(an+b).
+// If last is true, implements :nth-last-child instead.
+// If ofType is true, implements :nth-of-type instead.
+func nthChildMatch(a, b int, last, ofType bool, n *html.Node) bool {
+	if n.Type != html.ElementNode {
+		return false
+	}
+
+	parent := n.Parent
+	if parent == nil {
+		return false
+	}
+
+	if parent.Type == html.DocumentNode {
+		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
+}
+
+// simpleNthChildMatch implements :nth-child(b).
+// If ofType is true, implements :nth-of-type instead.
+func simpleNthChildMatch(b int, ofType bool, n *html.Node) bool {
+	if n.Type != html.ElementNode {
+		return false
+	}
+
+	parent := n.Parent
+	if parent == nil {
+		return false
+	}
+
+	if parent.Type == html.DocumentNode {
+		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 c == n {
+			return count == b
+		}
+		if count >= b {
+			return false
+		}
+	}
+	return false
+}
+
+// simpleNthLastChildMatch implements :nth-last-child(b).
+// If ofType is true, implements :nth-last-of-type instead.
+func simpleNthLastChildMatch(b int, ofType bool, n *html.Node) bool {
+	if n.Type != html.ElementNode {
+		return false
+	}
+
+	parent := n.Parent
+	if parent == nil {
+		return false
+	}
+
+	if parent.Type == html.DocumentNode {
+		return false
+	}
+
+	count := 0
+	for c := parent.LastChild; c != nil; c = c.PrevSibling {
+		if c.Type != html.ElementNode || (ofType && c.Data != n.Data) {
+			continue
+		}
+		count++
+		if c == n {
+			return count == b
+		}
+		if count >= b {
+			return false
+		}
+	}
+	return false
+}
+
+// Specificity for nth-child pseudo-class.
+// Does not support a list of selectors
+func (s nthPseudoClassSelector) Specificity() Specificity {
+	return Specificity{0, 1, 0}
+}
+
+type onlyChildPseudoClassSelector struct {
+	ofType bool
+}
+
+// Match implements :only-child.
+// If `ofType` is true, it implements :only-of-type instead.
+func (s onlyChildPseudoClassSelector) Match(n *html.Node) bool {
+	if n.Type != html.ElementNode {
+		return false
+	}
+
+	parent := n.Parent
+	if parent == nil {
+		return false
+	}
+
+	if parent.Type == html.DocumentNode {
+		return false
+	}
+
+	count := 0
+	for c := parent.FirstChild; c != nil; c = c.NextSibling {
+		if (c.Type != html.ElementNode) || (s.ofType && c.Data != n.Data) {
+			continue
+		}
+		count++
+		if count > 1 {
+			return false
+		}
+	}
+
+	return count == 1
+}
+
+func (s onlyChildPseudoClassSelector) Specificity() Specificity {
+	return Specificity{0, 1, 0}
+}
+
+type inputPseudoClassSelector struct{}
+
+// Matches input, select, textarea and button elements.
+func (s inputPseudoClassSelector) Match(n *html.Node) bool {
+	return n.Type == html.ElementNode && (n.Data == "input" || n.Data == "select" || n.Data == "textarea" || n.Data == "button")
+}
+
+func (s inputPseudoClassSelector) Specificity() Specificity {
+	return Specificity{0, 1, 0}
+}
+
+type emptyElementPseudoClassSelector struct{}
+
+// Matches empty elements.
+func (s emptyElementPseudoClassSelector) Match(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
+}
+
+func (s emptyElementPseudoClassSelector) Specificity() Specificity {
+	return Specificity{0, 1, 0}
+}
+
+type rootPseudoClassSelector struct{}
+
+// Match implements :root
+func (s rootPseudoClassSelector) Match(n *html.Node) bool {
+	if n.Type != html.ElementNode {
+		return false
+	}
+	if n.Parent == nil {
+		return false
+	}
+	return n.Parent.Type == html.DocumentNode
+}
+
+func (s rootPseudoClassSelector) Specificity() Specificity {
+	return Specificity{0, 1, 0}
+}
+
+type compoundSelector struct {
+	selectors []Sel
+}
+
+// Matches elements if each sub-selectors matches.
+func (t compoundSelector) Match(n *html.Node) bool {
+	if len(t.selectors) == 0 {
+		return n.Type == html.ElementNode
+	}
+
+	for _, sel := range t.selectors {
+		if !sel.Match(n) {
+			return false
+		}
+	}
+	return true
+}
+
+func (s compoundSelector) Specificity() Specificity {
+	var out Specificity
+	for _, sel := range s.selectors {
+		out = out.Add(sel.Specificity())
+	}
+	return out
+}
+
+type combinedSelector struct {
+	first      Sel
+	combinator byte
+	second     Sel
+}
+
+func (t combinedSelector) Match(n *html.Node) bool {
+	if t.first == nil {
+		return false // maybe we should panic
+	}
+	switch t.combinator {
+	case 0:
+		return t.first.Match(n)
+	case ' ':
+		return descendantMatch(t.first, t.second, n)
+	case '>':
+		return childMatch(t.first, t.second, n)
+	case '+':
+		return siblingMatch(t.first, t.second, true, n)
+	case '~':
+		return siblingMatch(t.first, t.second, false, n)
+	default:
+		panic("unknown combinator")
+	}
+}
+
+// matches an element if it matches d and has an ancestor that matches a.
+func descendantMatch(a, d Matcher, n *html.Node) bool {
+	if !d.Match(n) {
+		return false
+	}
+
+	for p := n.Parent; p != nil; p = p.Parent {
+		if a.Match(p) {
+			return true
+		}
+	}
+
+	return false
+}
+
+// matches an element if it matches d and its parent matches a.
+func childMatch(a, d Matcher, n *html.Node) bool {
+	return d.Match(n) && n.Parent != nil && a.Match(n.Parent)
+}
+
+// matches an element if it matches s2 and is preceded by an element that matches s1.
+// If adjacent is true, the sibling must be immediately before the element.
+func siblingMatch(s1, s2 Matcher, adjacent bool, n *html.Node) bool {
+	if !s2.Match(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.Match(n)
+		}
+		return false
+	}
+
+	// Walk backwards looking for element that matches s1
+	for c := n.PrevSibling; c != nil; c = c.PrevSibling {
+		if s1.Match(c) {
+			return true
+		}
+	}
+
+	return false
+}
+
+func (s combinedSelector) Specificity() Specificity {
+	spec := s.first.Specificity()
+	if s.second != nil {
+		spec = spec.Add(s.second.Specificity())
+	}
+	return spec
+}
+
+// A SelectorGroup is a list of selectors, which matches if any of the
+// individual selectors matches.
+type SelectorGroup []Sel
+
+// Match returns true if the node matches one of the single selectors.
+func (s SelectorGroup) Match(n *html.Node) bool {
+	for _, sel := range s {
+		if sel.Match(n) {
+			return true
+		}
+	}
+	return false
+}

vendor/github.com/andybalholm/cascadia/specificity.go

@@ -0,0 +1,26 @@
+package cascadia
+
+// Specificity is the CSS specificity as defined in
+// https://www.w3.org/TR/selectors/#specificity-rules
+// with the convention Specificity = [A,B,C].
+type Specificity [3]int
+
+// returns `true` if s < other (strictly), false otherwise
+func (s Specificity) Less(other Specificity) bool {
+	for i := range s {
+		if s[i] < other[i] {
+			return true
+		}
+		if s[i] > other[i] {
+			return false
+		}
+	}
+	return false
+}
+
+func (s Specificity) Add(other Specificity) Specificity {
+	for i, sp := range other {
+		s[i] += sp
+	}
+	return s
+}