Fix code quality violations and exclude Manifest from checks

Document application modes (development/debug/production)
Add global file drop handler, order column normalization, SPA hash fix
Serve CDN assets via /_vendor/ URLs instead of merging into bundles
Add production minification with license preservation
Improve JSON formatting for debugging and production optimization
Add CDN asset caching with CSS URL inlining for production builds
Add three-mode system (development, debug, production)
Update Manifest CLAUDE.md to reflect helper class architecture
Refactor Manifest.php into helper classes for better organization
Pre-manifest-refactor checkpoint: Add app_mode documentation

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <noreply@anthropic.com>

node_modules/css-tree/cjs/definition-syntax/SyntaxError.cjs

@@ -0,0 +1,16 @@
+'use strict';
+
+const createCustomError = require('../utils/create-custom-error.cjs');
+
+function SyntaxError(message, input, offset) {
+    return Object.assign(createCustomError.createCustomError('SyntaxError', message), {
+        input,
+        offset,
+        rawMessage: message,
+        message: message + '\n' +
+            '  ' + input + '\n' +
+            '--' + new Array((offset || input.length) + 1).join('-') + '^'
+    });
+}
+
+exports.SyntaxError = SyntaxError;

node_modules/css-tree/cjs/definition-syntax/generate.cjs

@@ -0,0 +1,139 @@
+'use strict';
+
+function noop(value) {
+    return value;
+}
+
+function generateMultiplier(multiplier) {
+    const { min, max, comma } = multiplier;
+
+    if (min === 0 && max === 0) {
+        return comma ? '#?' : '*';
+    }
+
+    if (min === 0 && max === 1) {
+        return '?';
+    }
+
+    if (min === 1 && max === 0) {
+        return comma ? '#' : '+';
+    }
+
+    if (min === 1 && max === 1) {
+        return '';
+    }
+
+    return (
+        (comma ? '#' : '') +
+        (min === max
+            ? '{' + min + '}'
+            : '{' + min + ',' + (max !== 0 ? max : '') + '}'
+        )
+    );
+}
+
+function generateTypeOpts(node) {
+    switch (node.type) {
+        case 'Range':
+            return (
+                ' [' +
+                (node.min === null ? '-∞' : node.min) +
+                ',' +
+                (node.max === null ? '∞' : node.max) +
+                ']'
+            );
+
+        default:
+            throw new Error('Unknown node type `' + node.type + '`');
+    }
+}
+
+function generateSequence(node, decorate, forceBraces, compact) {
+    const combinator = node.combinator === ' ' || compact ? node.combinator : ' ' + node.combinator + ' ';
+    const result = node.terms
+        .map(term => internalGenerate(term, decorate, forceBraces, compact))
+        .join(combinator);
+
+    if (node.explicit || forceBraces) {
+        return (compact || result[0] === ',' ? '[' : '[ ') + result + (compact ? ']' : ' ]');
+    }
+
+    return result;
+}
+
+function internalGenerate(node, decorate, forceBraces, compact) {
+    let result;
+
+    switch (node.type) {
+        case 'Group':
+            result =
+                generateSequence(node, decorate, forceBraces, compact) +
+                (node.disallowEmpty ? '!' : '');
+            break;
+
+        case 'Multiplier':
+            // return since node is a composition
+            return (
+                internalGenerate(node.term, decorate, forceBraces, compact) +
+                decorate(generateMultiplier(node), node)
+            );
+
+        case 'Boolean':
+            result = '<boolean-expr[' + internalGenerate(node.term, decorate, forceBraces, compact) + ']>';
+            break;
+
+        case 'Type':
+            result = '<' + node.name + (node.opts ? decorate(generateTypeOpts(node.opts), node.opts) : '') + '>';
+            break;
+
+        case 'Property':
+            result = '<\'' + node.name + '\'>';
+            break;
+
+        case 'Keyword':
+            result = node.name;
+            break;
+
+        case 'AtKeyword':
+            result = '@' + node.name;
+            break;
+
+        case 'Function':
+            result = node.name + '(';
+            break;
+
+        case 'String':
+        case 'Token':
+            result = node.value;
+            break;
+
+        case 'Comma':
+            result = ',';
+            break;
+
+        default:
+            throw new Error('Unknown node type `' + node.type + '`');
+    }
+
+    return decorate(result, node);
+}
+
+function generate(node, options) {
+    let decorate = noop;
+    let forceBraces = false;
+    let compact = false;
+
+    if (typeof options === 'function') {
+        decorate = options;
+    } else if (options) {
+        forceBraces = Boolean(options.forceBraces);
+        compact = Boolean(options.compact);
+        if (typeof options.decorate === 'function') {
+            decorate = options.decorate;
+        }
+    }
+
+    return internalGenerate(node, decorate, forceBraces, compact);
+}
+
+exports.generate = generate;

node_modules/css-tree/cjs/definition-syntax/index.cjs

@@ -0,0 +1,13 @@
+'use strict';
+
+const SyntaxError = require('./SyntaxError.cjs');
+const generate = require('./generate.cjs');
+const parse = require('./parse.cjs');
+const walk = require('./walk.cjs');
+
+
+
+exports.SyntaxError = SyntaxError.SyntaxError;
+exports.generate = generate.generate;
+exports.parse = parse.parse;
+exports.walk = walk.walk;

node_modules/css-tree/cjs/definition-syntax/parse.cjs

@@ -0,0 +1,556 @@
+'use strict';
+
+const scanner = require('./scanner.cjs');
+
+const TAB = 9;
+const N = 10;
+const F = 12;
+const R = 13;
+const SPACE = 32;
+const EXCLAMATIONMARK = 33;    // !
+const NUMBERSIGN = 35;         // #
+const AMPERSAND = 38;          // &
+const APOSTROPHE = 39;         // '
+const LEFTPARENTHESIS = 40;    // (
+const RIGHTPARENTHESIS = 41;   // )
+const ASTERISK = 42;           // *
+const PLUSSIGN = 43;           // +
+const COMMA = 44;              // ,
+const HYPERMINUS = 45;         // -
+const LESSTHANSIGN = 60;       // <
+const GREATERTHANSIGN = 62;    // >
+const QUESTIONMARK = 63;       // ?
+const COMMERCIALAT = 64;       // @
+const LEFTSQUAREBRACKET = 91;  // [
+const RIGHTSQUAREBRACKET = 93; // ]
+const LEFTCURLYBRACKET = 123;  // {
+const VERTICALLINE = 124;      // |
+const RIGHTCURLYBRACKET = 125; // }
+const INFINITY = 8734;         // ∞
+const COMBINATOR_PRECEDENCE = {
+    ' ': 1,
+    '&&': 2,
+    '||': 3,
+    '|': 4
+};
+
+function readMultiplierRange(scanner) {
+    let min = null;
+    let max = null;
+
+    scanner.eat(LEFTCURLYBRACKET);
+    scanner.skipWs();
+
+    min = scanner.scanNumber(scanner);
+    scanner.skipWs();
+
+    if (scanner.charCode() === COMMA) {
+        scanner.pos++;
+        scanner.skipWs();
+
+        if (scanner.charCode() !== RIGHTCURLYBRACKET) {
+            max = scanner.scanNumber(scanner);
+            scanner.skipWs();
+        }
+    } else {
+        max = min;
+    }
+
+    scanner.eat(RIGHTCURLYBRACKET);
+
+    return {
+        min: Number(min),
+        max: max ? Number(max) : 0
+    };
+}
+
+function readMultiplier(scanner) {
+    let range = null;
+    let comma = false;
+
+    switch (scanner.charCode()) {
+        case ASTERISK:
+            scanner.pos++;
+
+            range = {
+                min: 0,
+                max: 0
+            };
+
+            break;
+
+        case PLUSSIGN:
+            scanner.pos++;
+
+            range = {
+                min: 1,
+                max: 0
+            };
+
+            break;
+
+        case QUESTIONMARK:
+            scanner.pos++;
+
+            range = {
+                min: 0,
+                max: 1
+            };
+
+            break;
+
+        case NUMBERSIGN:
+            scanner.pos++;
+
+            comma = true;
+
+            if (scanner.charCode() === LEFTCURLYBRACKET) {
+                range = readMultiplierRange(scanner);
+            } else if (scanner.charCode() === QUESTIONMARK) {
+                // https://www.w3.org/TR/css-values-4/#component-multipliers
+                // > the # and ? multipliers may be stacked as #?
+                // In this case just treat "#?" as a single multiplier
+                // { min: 0, max: 0, comma: true }
+                scanner.pos++;
+                range = {
+                    min: 0,
+                    max: 0
+                };
+            } else {
+                range = {
+                    min: 1,
+                    max: 0
+                };
+            }
+
+            break;
+
+        case LEFTCURLYBRACKET:
+            range = readMultiplierRange(scanner);
+            break;
+
+        default:
+            return null;
+    }
+
+    return {
+        type: 'Multiplier',
+        comma,
+        min: range.min,
+        max: range.max,
+        term: null
+    };
+}
+
+function maybeMultiplied(scanner, node) {
+    const multiplier = readMultiplier(scanner);
+
+    if (multiplier !== null) {
+        multiplier.term = node;
+
+        // https://www.w3.org/TR/css-values-4/#component-multipliers
+        // > The + and # multipliers may be stacked as +#;
+        // Represent "+#" as nested multipliers:
+        // { ...<multiplier #>,
+        //   term: {
+        //     ...<multipler +>,
+        //     term: node
+        //   }
+        // }
+        if (scanner.charCode() === NUMBERSIGN &&
+            scanner.charCodeAt(scanner.pos - 1) === PLUSSIGN) {
+            return maybeMultiplied(scanner, multiplier);
+        }
+
+        return multiplier;
+    }
+
+    return node;
+}
+
+function maybeToken(scanner) {
+    const ch = scanner.peek();
+
+    if (ch === '') {
+        return null;
+    }
+
+    return maybeMultiplied(scanner, {
+        type: 'Token',
+        value: ch
+    });
+}
+
+function readProperty(scanner) {
+    let name;
+
+    scanner.eat(LESSTHANSIGN);
+    scanner.eat(APOSTROPHE);
+
+    name = scanner.scanWord();
+
+    scanner.eat(APOSTROPHE);
+    scanner.eat(GREATERTHANSIGN);
+
+    return maybeMultiplied(scanner, {
+        type: 'Property',
+        name
+    });
+}
+
+// https://drafts.csswg.org/css-values-3/#numeric-ranges
+// 4.1. Range Restrictions and Range Definition Notation
+//
+// Range restrictions can be annotated in the numeric type notation using CSS bracketed
+// range notation—[min,max]—within the angle brackets, after the identifying keyword,
+// indicating a closed range between (and including) min and max.
+// For example, <integer [0, 10]> indicates an integer between 0 and 10, inclusive.
+function readTypeRange(scanner) {
+    // use null for Infinity to make AST format JSON serializable/deserializable
+    let min = null; // -Infinity
+    let max = null; // Infinity
+    let sign = 1;
+
+    scanner.eat(LEFTSQUAREBRACKET);
+
+    if (scanner.charCode() === HYPERMINUS) {
+        scanner.peek();
+        sign = -1;
+    }
+
+    if (sign == -1 && scanner.charCode() === INFINITY) {
+        scanner.peek();
+    } else {
+        min = sign * Number(scanner.scanNumber(scanner));
+
+        if (scanner.isNameCharCode()) {
+            min += scanner.scanWord();
+        }
+    }
+
+    scanner.skipWs();
+    scanner.eat(COMMA);
+    scanner.skipWs();
+
+    if (scanner.charCode() === INFINITY) {
+        scanner.peek();
+    } else {
+        sign = 1;
+
+        if (scanner.charCode() === HYPERMINUS) {
+            scanner.peek();
+            sign = -1;
+        }
+
+        max = sign * Number(scanner.scanNumber(scanner));
+
+        if (scanner.isNameCharCode()) {
+            max += scanner.scanWord();
+        }
+    }
+
+    scanner.eat(RIGHTSQUAREBRACKET);
+
+    return {
+        type: 'Range',
+        min,
+        max
+    };
+}
+
+function readType(scanner) {
+    let name;
+    let opts = null;
+
+    scanner.eat(LESSTHANSIGN);
+    name = scanner.scanWord();
+
+    // https://drafts.csswg.org/css-values-5/#boolean
+    if (name === 'boolean-expr') {
+        scanner.eat(LEFTSQUAREBRACKET);
+
+        const implicitGroup = readImplicitGroup(scanner, RIGHTSQUAREBRACKET);
+
+        scanner.eat(RIGHTSQUAREBRACKET);
+        scanner.eat(GREATERTHANSIGN);
+
+        return maybeMultiplied(scanner, {
+            type: 'Boolean',
+            term: implicitGroup.terms.length === 1
+                ? implicitGroup.terms[0]
+                : implicitGroup
+        });
+    }
+
+    if (scanner.charCode() === LEFTPARENTHESIS &&
+        scanner.nextCharCode() === RIGHTPARENTHESIS) {
+        scanner.pos += 2;
+        name += '()';
+    }
+
+    if (scanner.charCodeAt(scanner.findWsEnd(scanner.pos)) === LEFTSQUAREBRACKET) {
+        scanner.skipWs();
+        opts = readTypeRange(scanner);
+    }
+
+    scanner.eat(GREATERTHANSIGN);
+
+    return maybeMultiplied(scanner, {
+        type: 'Type',
+        name,
+        opts
+    });
+}
+
+function readKeywordOrFunction(scanner) {
+    const name = scanner.scanWord();
+
+    if (scanner.charCode() === LEFTPARENTHESIS) {
+        scanner.pos++;
+
+        return {
+            type: 'Function',
+            name
+        };
+    }
+
+    return maybeMultiplied(scanner, {
+        type: 'Keyword',
+        name
+    });
+}
+
+function regroupTerms(terms, combinators) {
+    function createGroup(terms, combinator) {
+        return {
+            type: 'Group',
+            terms,
+            combinator,
+            disallowEmpty: false,
+            explicit: false
+        };
+    }
+
+    let combinator;
+
+    combinators = Object.keys(combinators)
+        .sort((a, b) => COMBINATOR_PRECEDENCE[a] - COMBINATOR_PRECEDENCE[b]);
+
+    while (combinators.length > 0) {
+        combinator = combinators.shift();
+
+        let i = 0;
+        let subgroupStart = 0;
+
+        for (; i < terms.length; i++) {
+            const term = terms[i];
+
+            if (term.type === 'Combinator') {
+                if (term.value === combinator) {
+                    if (subgroupStart === -1) {
+                        subgroupStart = i - 1;
+                    }
+                    terms.splice(i, 1);
+                    i--;
+                } else {
+                    if (subgroupStart !== -1 && i - subgroupStart > 1) {
+                        terms.splice(
+                            subgroupStart,
+                            i - subgroupStart,
+                            createGroup(terms.slice(subgroupStart, i), combinator)
+                        );
+                        i = subgroupStart + 1;
+                    }
+                    subgroupStart = -1;
+                }
+            }
+        }
+
+        if (subgroupStart !== -1 && combinators.length) {
+            terms.splice(
+                subgroupStart,
+                i - subgroupStart,
+                createGroup(terms.slice(subgroupStart, i), combinator)
+            );
+        }
+    }
+
+    return combinator;
+}
+
+function readImplicitGroup(scanner, stopCharCode) {
+    const combinators = Object.create(null);
+    const terms = [];
+    let token;
+    let prevToken = null;
+    let prevTokenPos = scanner.pos;
+
+    while (scanner.charCode() !== stopCharCode && (token = peek(scanner, stopCharCode))) {
+        if (token.type !== 'Spaces') {
+            if (token.type === 'Combinator') {
+                // check for combinator in group beginning and double combinator sequence
+                if (prevToken === null || prevToken.type === 'Combinator') {
+                    scanner.pos = prevTokenPos;
+                    scanner.error('Unexpected combinator');
+                }
+
+                combinators[token.value] = true;
+            } else if (prevToken !== null && prevToken.type !== 'Combinator') {
+                combinators[' '] = true;  // a b
+                terms.push({
+                    type: 'Combinator',
+                    value: ' '
+                });
+            }
+
+            terms.push(token);
+            prevToken = token;
+            prevTokenPos = scanner.pos;
+        }
+    }
+
+    // check for combinator in group ending
+    if (prevToken !== null && prevToken.type === 'Combinator') {
+        scanner.pos -= prevTokenPos;
+        scanner.error('Unexpected combinator');
+    }
+
+    return {
+        type: 'Group',
+        terms,
+        combinator: regroupTerms(terms, combinators) || ' ',
+        disallowEmpty: false,
+        explicit: false
+    };
+}
+
+function readGroup(scanner, stopCharCode) {
+    let result;
+
+    scanner.eat(LEFTSQUAREBRACKET);
+    result = readImplicitGroup(scanner, stopCharCode);
+    scanner.eat(RIGHTSQUAREBRACKET);
+
+    result.explicit = true;
+
+    if (scanner.charCode() === EXCLAMATIONMARK) {
+        scanner.pos++;
+        result.disallowEmpty = true;
+    }
+
+    return result;
+}
+
+function peek(scanner, stopCharCode) {
+    let code = scanner.charCode();
+
+    switch (code) {
+        case RIGHTSQUAREBRACKET:
+            // don't eat, stop scan a group
+            break;
+
+        case LEFTSQUAREBRACKET:
+            return maybeMultiplied(scanner, readGroup(scanner, stopCharCode));
+
+        case LESSTHANSIGN:
+            return scanner.nextCharCode() === APOSTROPHE
+                ? readProperty(scanner)
+                : readType(scanner);
+
+        case VERTICALLINE:
+            return {
+                type: 'Combinator',
+                value: scanner.substringToPos(
+                    scanner.pos + (scanner.nextCharCode() === VERTICALLINE ? 2 : 1)
+                )
+            };
+
+        case AMPERSAND:
+            scanner.pos++;
+            scanner.eat(AMPERSAND);
+
+            return {
+                type: 'Combinator',
+                value: '&&'
+            };
+
+        case COMMA:
+            scanner.pos++;
+            return {
+                type: 'Comma'
+            };
+
+        case APOSTROPHE:
+            return maybeMultiplied(scanner, {
+                type: 'String',
+                value: scanner.scanString()
+            });
+
+        case SPACE:
+        case TAB:
+        case N:
+        case R:
+        case F:
+            return {
+                type: 'Spaces',
+                value: scanner.scanSpaces()
+            };
+
+        case COMMERCIALAT:
+            code = scanner.nextCharCode();
+
+            if (scanner.isNameCharCode(code)) {
+                scanner.pos++;
+                return {
+                    type: 'AtKeyword',
+                    name: scanner.scanWord()
+                };
+            }
+
+            return maybeToken(scanner);
+
+        case ASTERISK:
+        case PLUSSIGN:
+        case QUESTIONMARK:
+        case NUMBERSIGN:
+        case EXCLAMATIONMARK:
+            // prohibited tokens (used as a multiplier start)
+            break;
+
+        case LEFTCURLYBRACKET:
+            // LEFTCURLYBRACKET is allowed since mdn/data uses it w/o quoting
+            // check next char isn't a number, because it's likely a disjoined multiplier
+            code = scanner.nextCharCode();
+
+            if (code < 48 || code > 57) {
+                return maybeToken(scanner);
+            }
+
+            break;
+
+        default:
+            if (scanner.isNameCharCode(code)) {
+                return readKeywordOrFunction(scanner);
+            }
+
+            return maybeToken(scanner);
+    }
+}
+
+function parse(source) {
+    const scanner$1 = new scanner.Scanner(source);
+    const result = readImplicitGroup(scanner$1);
+
+    if (scanner$1.pos !== source.length) {
+        scanner$1.error('Unexpected input');
+    }
+
+    // reduce redundant groups with single group term
+    if (result.terms.length === 1 && result.terms[0].type === 'Group') {
+        return result.terms[0];
+    }
+
+    return result;
+}
+
+exports.parse = parse;

node_modules/css-tree/cjs/definition-syntax/scanner.cjs

@@ -0,0 +1,113 @@
+'use strict';
+
+const SyntaxError = require('./SyntaxError.cjs');
+
+const TAB = 9;
+const N = 10;
+const F = 12;
+const R = 13;
+const SPACE = 32;
+const NAME_CHAR = new Uint8Array(128).map((_, idx) =>
+    /[a-zA-Z0-9\-]/.test(String.fromCharCode(idx)) ? 1 : 0
+);
+
+class Scanner {
+    constructor(str) {
+        this.str = str;
+        this.pos = 0;
+    }
+
+    charCodeAt(pos) {
+        return pos < this.str.length ? this.str.charCodeAt(pos) : 0;
+    }
+    charCode() {
+        return this.charCodeAt(this.pos);
+    }
+    isNameCharCode(code = this.charCode()) {
+        return code < 128 && NAME_CHAR[code] === 1;
+    }
+    nextCharCode() {
+        return this.charCodeAt(this.pos + 1);
+    }
+    nextNonWsCode(pos) {
+        return this.charCodeAt(this.findWsEnd(pos));
+    }
+    skipWs() {
+        this.pos = this.findWsEnd(this.pos);
+    }
+    findWsEnd(pos) {
+        for (; pos < this.str.length; pos++) {
+            const code = this.str.charCodeAt(pos);
+            if (code !== R && code !== N && code !== F && code !== SPACE && code !== TAB) {
+                break;
+            }
+        }
+
+        return pos;
+    }
+    substringToPos(end) {
+        return this.str.substring(this.pos, this.pos = end);
+    }
+    eat(code) {
+        if (this.charCode() !== code) {
+            this.error('Expect `' + String.fromCharCode(code) + '`');
+        }
+
+        this.pos++;
+    }
+    peek() {
+        return this.pos < this.str.length ? this.str.charAt(this.pos++) : '';
+    }
+    error(message) {
+        throw new SyntaxError.SyntaxError(message, this.str, this.pos);
+    }
+
+    scanSpaces() {
+        return this.substringToPos(this.findWsEnd(this.pos));
+    }
+    scanWord() {
+        let end = this.pos;
+
+        for (; end < this.str.length; end++) {
+            const code = this.str.charCodeAt(end);
+            if (code >= 128 || NAME_CHAR[code] === 0) {
+                break;
+            }
+        }
+
+        if (this.pos === end) {
+            this.error('Expect a keyword');
+        }
+
+        return this.substringToPos(end);
+    }
+    scanNumber() {
+        let end = this.pos;
+
+        for (; end < this.str.length; end++) {
+            const code = this.str.charCodeAt(end);
+
+            if (code < 48 || code > 57) {
+                break;
+            }
+        }
+
+        if (this.pos === end) {
+            this.error('Expect a number');
+        }
+
+        return this.substringToPos(end);
+    }
+    scanString() {
+        const end = this.str.indexOf('\'', this.pos + 1);
+
+        if (end === -1) {
+            this.pos = this.str.length;
+            this.error('Expect an apostrophe');
+        }
+
+        return this.substringToPos(end + 1);
+    }
+}
+
+exports.Scanner = Scanner;

node_modules/css-tree/cjs/definition-syntax/tokenizer.cjs

@@ -0,0 +1,59 @@
+'use strict';
+
+const SyntaxError = require('./SyntaxError.cjs');
+
+const TAB = 9;
+const N = 10;
+const F = 12;
+const R = 13;
+const SPACE = 32;
+
+class Tokenizer {
+    constructor(str) {
+        this.str = str;
+        this.pos = 0;
+    }
+    charCodeAt(pos) {
+        return pos < this.str.length ? this.str.charCodeAt(pos) : 0;
+    }
+    charCode() {
+        return this.charCodeAt(this.pos);
+    }
+    nextCharCode() {
+        return this.charCodeAt(this.pos + 1);
+    }
+    nextNonWsCode(pos) {
+        return this.charCodeAt(this.findWsEnd(pos));
+    }
+    skipWs() {
+        this.pos = this.findWsEnd(this.pos);
+    }
+    findWsEnd(pos) {
+        for (; pos < this.str.length; pos++) {
+            const code = this.str.charCodeAt(pos);
+            if (code !== R && code !== N && code !== F && code !== SPACE && code !== TAB) {
+                break;
+            }
+        }
+
+        return pos;
+    }
+    substringToPos(end) {
+        return this.str.substring(this.pos, this.pos = end);
+    }
+    eat(code) {
+        if (this.charCode() !== code) {
+            this.error('Expect `' + String.fromCharCode(code) + '`');
+        }
+
+        this.pos++;
+    }
+    peek() {
+        return this.pos < this.str.length ? this.str.charAt(this.pos++) : '';
+    }
+    error(message) {
+        throw new SyntaxError.SyntaxError(message, this.str, this.pos);
+    }
+}
+
+exports.Tokenizer = Tokenizer;

node_modules/css-tree/cjs/definition-syntax/walk.cjs

@@ -0,0 +1,57 @@
+'use strict';
+
+const noop = function() {};
+
+function ensureFunction(value) {
+    return typeof value === 'function' ? value : noop;
+}
+
+function walk(node, options, context) {
+    function walk(node) {
+        enter.call(context, node);
+
+        switch (node.type) {
+            case 'Group':
+                node.terms.forEach(walk);
+                break;
+
+            case 'Multiplier':
+            case 'Boolean':
+                walk(node.term);
+                break;
+
+            case 'Type':
+            case 'Property':
+            case 'Keyword':
+            case 'AtKeyword':
+            case 'Function':
+            case 'String':
+            case 'Token':
+            case 'Comma':
+                break;
+
+            default:
+                throw new Error('Unknown type: ' + node.type);
+        }
+
+        leave.call(context, node);
+    }
+
+    let enter = noop;
+    let leave = noop;
+
+    if (typeof options === 'function') {
+        enter = options;
+    } else if (options) {
+        enter = ensureFunction(options.enter);
+        leave = ensureFunction(options.leave);
+    }
+
+    if (enter === noop && leave === noop) {
+        throw new Error('Neither `enter` nor `leave` walker handler is set or both aren\'t a function');
+    }
+
+    walk(node);
+}
+
+exports.walk = walk;