postcss,(plugins): nanocss, postcss-preset-env

13 files changed, 1673 insertions, 0 deletions

diff --git a/node_modules/csso/lib/restructure/1-mergeAtrule.js b/node_modules/csso/lib/restructure/1-mergeAtrule.js
new file mode 100644
index 00000000..e00e4d32
--- /dev/null
+++ b/node_modules/csso/lib/restructure/1-mergeAtrule.js
@@ -0,0 +1,106 @@
+import { List, walk, keyword as resolveKeyword } from 'css-tree';
+
+const { hasOwnProperty } = Object.prototype;
+
+function addRuleToMap(map, item, list, single) {
+    const node = item.data;
+    const name = resolveKeyword(node.name).basename;
+    const id = node.name.toLowerCase() + '/' + (node.prelude ? node.prelude.id : null);
+
+    if (!hasOwnProperty.call(map, name)) {
+        map[name] = Object.create(null);
+    }
+
+    if (single) {
+        delete map[name][id];
+    }
+
+    if (!hasOwnProperty.call(map[name], id)) {
+        map[name][id] = new List();
+    }
+
+    map[name][id].append(list.remove(item));
+}
+
+function relocateAtrules(ast, options) {
+    const collected = Object.create(null);
+    let topInjectPoint = null;
+
+    ast.children.forEach(function(node, item, list) {
+        if (node.type === 'Atrule') {
+            const name = resolveKeyword(node.name).basename;
+
+            switch (name) {
+                case 'keyframes':
+                    addRuleToMap(collected, item, list, true);
+                    return;
+
+                case 'media':
+                    if (options.forceMediaMerge) {
+                        addRuleToMap(collected, item, list, false);
+                        return;
+                    }
+                    break;
+            }
+
+            if (topInjectPoint === null &&
+                name !== 'charset' &&
+                name !== 'import') {
+                topInjectPoint = item;
+            }
+        } else {
+            if (topInjectPoint === null) {
+                topInjectPoint = item;
+            }
+        }
+    });
+
+    for (const atrule in collected) {
+        for (const id in collected[atrule]) {
+            ast.children.insertList(
+                collected[atrule][id],
+                atrule === 'media' ? null : topInjectPoint
+            );
+        }
+    }
+};
+
+function isMediaRule(node) {
+    return node.type === 'Atrule' && node.name === 'media';
+}
+
+function processAtrule(node, item, list) {
+    if (!isMediaRule(node)) {
+        return;
+    }
+
+    const prev = item.prev && item.prev.data;
+
+    if (!prev || !isMediaRule(prev)) {
+        return;
+    }
+
+    // merge @media with same query
+    if (node.prelude &&
+        prev.prelude &&
+        node.prelude.id === prev.prelude.id) {
+        prev.block.children.appendList(node.block.children);
+        list.remove(item);
+
+        // TODO: use it when we can refer to several points in source
+        // prev.loc = {
+        //     primary: prev.loc,
+        //     merged: node.loc
+        // };
+    }
+}
+
+export default function rejoinAtrule(ast, options) {
+    relocateAtrules(ast, options);
+
+    walk(ast, {
+        visit: 'Atrule',
+        reverse: true,
+        enter: processAtrule
+    });
+};
diff --git a/node_modules/csso/lib/restructure/2-initialMergeRuleset.js b/node_modules/csso/lib/restructure/2-initialMergeRuleset.js
new file mode 100644
index 00000000..c49abaa0
--- /dev/null
+++ b/node_modules/csso/lib/restructure/2-initialMergeRuleset.js
@@ -0,0 +1,53 @@
+import { walk } from 'css-tree';
+import {
+    unsafeToSkipNode,
+    isEqualSelectors,
+    isEqualDeclarations,
+    addSelectors,
+    hasSimilarSelectors
+} from './utils.js';
+
+function processRule(node, item, list) {
+    const selectors = node.prelude.children;
+    const declarations = node.block.children;
+
+    list.prevUntil(item.prev, function(prev) {
+        // skip non-ruleset node if safe
+        if (prev.type !== 'Rule') {
+            return unsafeToSkipNode.call(selectors, prev);
+        }
+
+        const prevSelectors = prev.prelude.children;
+        const prevDeclarations = prev.block.children;
+
+        // try to join rulesets with equal pseudo signature
+        if (node.pseudoSignature === prev.pseudoSignature) {
+            // try to join by selectors
+            if (isEqualSelectors(prevSelectors, selectors)) {
+                prevDeclarations.appendList(declarations);
+                list.remove(item);
+                return true;
+            }
+
+            // try to join by declarations
+            if (isEqualDeclarations(declarations, prevDeclarations)) {
+                addSelectors(prevSelectors, selectors);
+                list.remove(item);
+                return true;
+            }
+        }
+
+        // go to prev ruleset if has no selector similarities
+        return hasSimilarSelectors(selectors, prevSelectors);
+    });
+}
+
+// NOTE: direction should be left to right, since rulesets merge to left
+// ruleset. When direction right to left unmerged rulesets may prevent lookup
+// TODO: remove initial merge
+export default function initialMergeRule(ast) {
+    walk(ast, {
+        visit: 'Rule',
+        enter: processRule
+    });
+};
diff --git a/node_modules/csso/lib/restructure/3-disjoinRuleset.js b/node_modules/csso/lib/restructure/3-disjoinRuleset.js
new file mode 100644
index 00000000..02ec5e1f
--- /dev/null
+++ b/node_modules/csso/lib/restructure/3-disjoinRuleset.js
@@ -0,0 +1,42 @@
+import { List, walk } from 'css-tree';
+
+function processRule(node, item, list) {
+    const selectors = node.prelude.children;
+
+    // generate new rule sets:
+    // .a, .b { color: red; }
+    // ->
+    // .a { color: red; }
+    // .b { color: red; }
+
+    // while there are more than 1 simple selector split for rulesets
+    while (selectors.head !== selectors.tail) {
+        const newSelectors = new List();
+
+        newSelectors.insert(selectors.remove(selectors.head));
+
+        list.insert(list.createItem({
+            type: 'Rule',
+            loc: node.loc,
+            prelude: {
+                type: 'SelectorList',
+                loc: node.prelude.loc,
+                children: newSelectors
+            },
+            block: {
+                type: 'Block',
+                loc: node.block.loc,
+                children: node.block.children.copy()
+            },
+            pseudoSignature: node.pseudoSignature
+        }), item);
+    }
+}
+
+export default function disjoinRule(ast) {
+    walk(ast, {
+        visit: 'Rule',
+        reverse: true,
+        enter: processRule
+    });
+};
diff --git a/node_modules/csso/lib/restructure/4-restructShorthand.js b/node_modules/csso/lib/restructure/4-restructShorthand.js
new file mode 100644
index 00000000..41acb515
--- /dev/null
+++ b/node_modules/csso/lib/restructure/4-restructShorthand.js
@@ -0,0 +1,425 @@
+import { List, generate, walk } from 'css-tree';
+
+const REPLACE = 1;
+const REMOVE = 2;
+const TOP = 0;
+const RIGHT = 1;
+const BOTTOM = 2;
+const LEFT = 3;
+const SIDES = ['top', 'right', 'bottom', 'left'];
+const SIDE = {
+    'margin-top': 'top',
+    'margin-right': 'right',
+    'margin-bottom': 'bottom',
+    'margin-left': 'left',
+
+    'padding-top': 'top',
+    'padding-right': 'right',
+    'padding-bottom': 'bottom',
+    'padding-left': 'left',
+
+    'border-top-color': 'top',
+    'border-right-color': 'right',
+    'border-bottom-color': 'bottom',
+    'border-left-color': 'left',
+    'border-top-width': 'top',
+    'border-right-width': 'right',
+    'border-bottom-width': 'bottom',
+    'border-left-width': 'left',
+    'border-top-style': 'top',
+    'border-right-style': 'right',
+    'border-bottom-style': 'bottom',
+    'border-left-style': 'left'
+};
+const MAIN_PROPERTY = {
+    'margin': 'margin',
+    'margin-top': 'margin',
+    'margin-right': 'margin',
+    'margin-bottom': 'margin',
+    'margin-left': 'margin',
+
+    'padding': 'padding',
+    'padding-top': 'padding',
+    'padding-right': 'padding',
+    'padding-bottom': 'padding',
+    'padding-left': 'padding',
+
+    'border-color': 'border-color',
+    'border-top-color': 'border-color',
+    'border-right-color': 'border-color',
+    'border-bottom-color': 'border-color',
+    'border-left-color': 'border-color',
+    'border-width': 'border-width',
+    'border-top-width': 'border-width',
+    'border-right-width': 'border-width',
+    'border-bottom-width': 'border-width',
+    'border-left-width': 'border-width',
+    'border-style': 'border-style',
+    'border-top-style': 'border-style',
+    'border-right-style': 'border-style',
+    'border-bottom-style': 'border-style',
+    'border-left-style': 'border-style'
+};
+
+class TRBL {
+    constructor(name) {
+        this.name = name;
+        this.loc = null;
+        this.iehack = undefined;
+        this.sides = {
+            'top': null,
+            'right': null,
+            'bottom': null,
+            'left': null
+        };
+    }
+
+    getValueSequence(declaration, count) {
+        const values = [];
+        let iehack = '';
+        const hasBadValues = declaration.value.type !== 'Value' || declaration.value.children.some(function(child) {
+            let special = false;
+
+            switch (child.type) {
+                case 'Identifier':
+                    switch (child.name) {
+                        case '\\0':
+                        case '\\9':
+                            iehack = child.name;
+                            return;
+
+                        case 'inherit':
+                        case 'initial':
+                        case 'unset':
+                        case 'revert':
+                            special = child.name;
+                            break;
+                    }
+                    break;
+
+                case 'Dimension':
+                    switch (child.unit) {
+                        // is not supported until IE11
+                        case 'rem':
+
+                        // v* units is too buggy across browsers and better
+                        // don't merge values with those units
+                        case 'vw':
+                        case 'vh':
+                        case 'vmin':
+                        case 'vmax':
+                        case 'vm': // IE9 supporting "vm" instead of "vmin".
+                            special = child.unit;
+                            break;
+                    }
+                    break;
+
+                case 'Hash': // color
+                case 'Number':
+                case 'Percentage':
+                    break;
+
+                case 'Function':
+                    if (child.name === 'var') {
+                        return true;
+                    }
+
+                    special = child.name;
+                    break;
+
+                default:
+                    return true;  // bad value
+            }
+
+            values.push({
+                node: child,
+                special,
+                important: declaration.important
+            });
+        });
+
+        if (hasBadValues || values.length > count) {
+            return false;
+        }
+
+        if (typeof this.iehack === 'string' && this.iehack !== iehack) {
+            return false;
+        }
+
+        this.iehack = iehack; // move outside
+
+        return values;
+    }
+
+    canOverride(side, value) {
+        const currentValue = this.sides[side];
+
+        return !currentValue || (value.important && !currentValue.important);
+    }
+
+    add(name, declaration) {
+        function attemptToAdd() {
+            const sides = this.sides;
+            const side = SIDE[name];
+
+            if (side) {
+                if (side in sides === false) {
+                    return false;
+                }
+
+                const values = this.getValueSequence(declaration, 1);
+
+                if (!values || !values.length) {
+                    return false;
+                }
+
+                // can mix only if specials are equal
+                for (const key in sides) {
+                    if (sides[key] !== null && sides[key].special !== values[0].special) {
+                        return false;
+                    }
+                }
+
+                if (!this.canOverride(side, values[0])) {
+                    return true;
+                }
+
+                sides[side] = values[0];
+
+                return true;
+            } else if (name === this.name) {
+                const values = this.getValueSequence(declaration, 4);
+
+                if (!values || !values.length) {
+                    return false;
+                }
+
+                switch (values.length) {
+                    case 1:
+                        values[RIGHT] = values[TOP];
+                        values[BOTTOM] = values[TOP];
+                        values[LEFT] = values[TOP];
+                        break;
+
+                    case 2:
+                        values[BOTTOM] = values[TOP];
+                        values[LEFT] = values[RIGHT];
+                        break;
+
+                    case 3:
+                        values[LEFT] = values[RIGHT];
+                        break;
+                }
+
+                // can mix only if specials are equal
+                for (let i = 0; i < 4; i++) {
+                    for (const key in sides) {
+                        if (sides[key] !== null && sides[key].special !== values[i].special) {
+                            return false;
+                        }
+                    }
+                }
+
+                for (let i = 0; i < 4; i++) {
+                    if (this.canOverride(SIDES[i], values[i])) {
+                        sides[SIDES[i]] = values[i];
+                    }
+                }
+
+                return true;
+            }
+        }
+
+        if (!attemptToAdd.call(this)) {
+            return false;
+        }
+
+        // TODO: use it when we can refer to several points in source
+        // if (this.loc) {
+        //     this.loc = {
+        //         primary: this.loc,
+        //         merged: declaration.loc
+        //     };
+        // } else {
+        //     this.loc = declaration.loc;
+        // }
+        if (!this.loc) {
+            this.loc = declaration.loc;
+        }
+
+        return true;
+    }
+
+    isOkToMinimize() {
+        const top = this.sides.top;
+        const right = this.sides.right;
+        const bottom = this.sides.bottom;
+        const left = this.sides.left;
+
+        if (top && right && bottom && left) {
+            const important =
+                top.important +
+                right.important +
+                bottom.important +
+                left.important;
+
+            return important === 0 || important === 4;
+        }
+
+        return false;
+    }
+
+    getValue() {
+        const result = new List();
+        const sides = this.sides;
+        const values = [
+            sides.top,
+            sides.right,
+            sides.bottom,
+            sides.left
+        ];
+        const stringValues = [
+            generate(sides.top.node),
+            generate(sides.right.node),
+            generate(sides.bottom.node),
+            generate(sides.left.node)
+        ];
+
+        if (stringValues[LEFT] === stringValues[RIGHT]) {
+            values.pop();
+            if (stringValues[BOTTOM] === stringValues[TOP]) {
+                values.pop();
+                if (stringValues[RIGHT] === stringValues[TOP]) {
+                    values.pop();
+                }
+            }
+        }
+
+        for (let i = 0; i < values.length; i++) {
+            result.appendData(values[i].node);
+        }
+
+        if (this.iehack) {
+            result.appendData({
+                type: 'Identifier',
+                loc: null,
+                name: this.iehack
+            });
+        }
+
+        return {
+            type: 'Value',
+            loc: null,
+            children: result
+        };
+    }
+
+    getDeclaration() {
+        return {
+            type: 'Declaration',
+            loc: this.loc,
+            important: this.sides.top.important,
+            property: this.name,
+            value: this.getValue()
+        };
+    }
+}
+
+function processRule(rule, shorts, shortDeclarations, lastShortSelector) {
+    const declarations = rule.block.children;
+    const selector = rule.prelude.children.first.id;
+
+    rule.block.children.forEachRight(function(declaration, item) {
+        const property = declaration.property;
+
+        if (!MAIN_PROPERTY.hasOwnProperty(property)) {
+            return;
+        }
+
+        const key = MAIN_PROPERTY[property];
+        let shorthand;
+        let operation;
+
+        if (!lastShortSelector || selector === lastShortSelector) {
+            if (key in shorts) {
+                operation = REMOVE;
+                shorthand = shorts[key];
+            }
+        }
+
+        if (!shorthand || !shorthand.add(property, declaration)) {
+            operation = REPLACE;
+            shorthand = new TRBL(key);
+
+            // if can't parse value ignore it and break shorthand children
+            if (!shorthand.add(property, declaration)) {
+                lastShortSelector = null;
+                return;
+            }
+        }
+
+        shorts[key] = shorthand;
+        shortDeclarations.push({
+            operation,
+            block: declarations,
+            item,
+            shorthand
+        });
+
+        lastShortSelector = selector;
+    });
+
+    return lastShortSelector;
+}
+
+function processShorthands(shortDeclarations, markDeclaration) {
+    shortDeclarations.forEach(function(item) {
+        const shorthand = item.shorthand;
+
+        if (!shorthand.isOkToMinimize()) {
+            return;
+        }
+
+        if (item.operation === REPLACE) {
+            item.item.data = markDeclaration(shorthand.getDeclaration());
+        } else {
+            item.block.remove(item.item);
+        }
+    });
+}
+
+export default function restructBlock(ast, indexer) {
+    const stylesheetMap = {};
+    const shortDeclarations = [];
+
+    walk(ast, {
+        visit: 'Rule',
+        reverse: true,
+        enter(node) {
+            const stylesheet = this.block || this.stylesheet;
+            const ruleId = (node.pseudoSignature || '') + '|' + node.prelude.children.first.id;
+            let ruleMap;
+            let shorts;
+
+            if (!stylesheetMap.hasOwnProperty(stylesheet.id)) {
+                ruleMap = {
+                    lastShortSelector: null
+                };
+                stylesheetMap[stylesheet.id] = ruleMap;
+            } else {
+                ruleMap = stylesheetMap[stylesheet.id];
+            }
+
+            if (ruleMap.hasOwnProperty(ruleId)) {
+                shorts = ruleMap[ruleId];
+            } else {
+                shorts = {};
+                ruleMap[ruleId] = shorts;
+            }
+
+            ruleMap.lastShortSelector = processRule.call(this, node, shorts, shortDeclarations, ruleMap.lastShortSelector);
+        }
+    });
+
+    processShorthands(shortDeclarations, indexer.declaration);
+};
diff --git a/node_modules/csso/lib/restructure/6-restructBlock.js b/node_modules/csso/lib/restructure/6-restructBlock.js
new file mode 100644
index 00000000..7d5e8572
--- /dev/null
+++ b/node_modules/csso/lib/restructure/6-restructBlock.js
@@ -0,0 +1,308 @@
+import {
+    walk,
+    generate,
+    property as resolveProperty,
+    keyword as resolveKeyword
+} from 'css-tree';
+
+let fingerprintId = 1;
+const dontRestructure = new Set([
+    'src' // https://github.com/afelix/csso/issues/50
+]);
+
+const DONT_MIX_VALUE = {
+    // https://developer.mozilla.org/en-US/docs/Web/CSS/display#Browser_compatibility
+    'display': /table|ruby|flex|-(flex)?box$|grid|contents|run-in/i,
+    // https://developer.mozilla.org/en/docs/Web/CSS/text-align
+    'text-align': /^(start|end|match-parent|justify-all)$/i
+};
+
+const SAFE_VALUES = {
+    cursor: [
+        'auto', 'crosshair', 'default', 'move', 'text', 'wait', 'help',
+        'n-resize', 'e-resize', 's-resize', 'w-resize',
+        'ne-resize', 'nw-resize', 'se-resize', 'sw-resize',
+        'pointer', 'progress', 'not-allowed', 'no-drop', 'vertical-text', 'all-scroll',
+        'col-resize', 'row-resize'
+    ],
+    overflow: [
+        'hidden', 'visible', 'scroll', 'auto'
+    ],
+    position: [
+        'static', 'relative', 'absolute', 'fixed'
+    ]
+};
+
+const NEEDLESS_TABLE = {
+    'border-width': ['border'],
+    'border-style': ['border'],
+    'border-color': ['border'],
+    'border-top': ['border'],
+    'border-right': ['border'],
+    'border-bottom': ['border'],
+    'border-left': ['border'],
+    'border-top-width': ['border-top', 'border-width', 'border'],
+    'border-right-width': ['border-right', 'border-width', 'border'],
+    'border-bottom-width': ['border-bottom', 'border-width', 'border'],
+    'border-left-width': ['border-left', 'border-width', 'border'],
+    'border-top-style': ['border-top', 'border-style', 'border'],
+    'border-right-style': ['border-right', 'border-style', 'border'],
+    'border-bottom-style': ['border-bottom', 'border-style', 'border'],
+    'border-left-style': ['border-left', 'border-style', 'border'],
+    'border-top-color': ['border-top', 'border-color', 'border'],
+    'border-right-color': ['border-right', 'border-color', 'border'],
+    'border-bottom-color': ['border-bottom', 'border-color', 'border'],
+    'border-left-color': ['border-left', 'border-color', 'border'],
+    'margin-top': ['margin'],
+    'margin-right': ['margin'],
+    'margin-bottom': ['margin'],
+    'margin-left': ['margin'],
+    'padding-top': ['padding'],
+    'padding-right': ['padding'],
+    'padding-bottom': ['padding'],
+    'padding-left': ['padding'],
+    'font-style': ['font'],
+    'font-variant': ['font'],
+    'font-weight': ['font'],
+    'font-size': ['font'],
+    'font-family': ['font'],
+    'list-style-type': ['list-style'],
+    'list-style-position': ['list-style'],
+    'list-style-image': ['list-style']
+};
+
+function getPropertyFingerprint(propertyName, declaration, fingerprints) {
+    const realName = resolveProperty(propertyName).basename;
+
+    if (realName === 'background') {
+        return propertyName + ':' + generate(declaration.value);
+    }
+
+    const declarationId = declaration.id;
+    let fingerprint = fingerprints[declarationId];
+
+    if (!fingerprint) {
+        switch (declaration.value.type) {
+            case 'Value':
+                const special = {};
+                let vendorId = '';
+                let iehack = '';
+                let raw = false;
+
+                declaration.value.children.forEach(function walk(node) {
+                    switch (node.type) {
+                        case 'Value':
+                        case 'Brackets':
+                        case 'Parentheses':
+                            node.children.forEach(walk);
+                            break;
+
+                        case 'Raw':
+                            raw = true;
+                            break;
+
+                        case 'Identifier': {
+                            const { name } = node;
+
+                            if (!vendorId) {
+                                vendorId = resolveKeyword(name).vendor;
+                            }
+
+                            if (/\\[09]/.test(name)) {
+                                iehack = RegExp.lastMatch;
+                            }
+
+                            if (SAFE_VALUES.hasOwnProperty(realName)) {
+                                if (SAFE_VALUES[realName].indexOf(name) === -1) {
+                                    special[name] = true;
+                                }
+                            } else if (DONT_MIX_VALUE.hasOwnProperty(realName)) {
+                                if (DONT_MIX_VALUE[realName].test(name)) {
+                                    special[name] = true;
+                                }
+                            }
+
+                            break;
+                        }
+
+                        case 'Function': {
+                            let { name } = node;
+
+                            if (!vendorId) {
+                                vendorId = resolveKeyword(name).vendor;
+                            }
+
+                            if (name === 'rect') {
+                                // there are 2 forms of rect:
+                                //   rect(<top>, <right>, <bottom>, <left>) - standart
+                                //   rect(<top> <right> <bottom> <left>) – backwards compatible syntax
+                                // only the same form values can be merged
+                                const hasComma = node.children.some((node) =>
+                                    node.type === 'Operator' && node.value === ','
+                                );
+
+                                if (!hasComma) {
+                                    name = 'rect-backward';
+                                }
+                            }
+
+                            special[name + '()'] = true;
+
+                            // check nested tokens too
+                            node.children.forEach(walk);
+
+                            break;
+                        }
+
+                        case 'Dimension': {
+                            const { unit } = node;
+
+                            if (/\\[09]/.test(unit)) {
+                                iehack = RegExp.lastMatch;
+                            }
+
+                            switch (unit) {
+                                // is not supported until IE11
+                                case 'rem':
+
+                                // v* units is too buggy across browsers and better
+                                // don't merge values with those units
+                                case 'vw':
+                                case 'vh':
+                                case 'vmin':
+                                case 'vmax':
+                                case 'vm': // IE9 supporting "vm" instead of "vmin".
+                                    special[unit] = true;
+                                    break;
+                            }
+
+                            break;
+                        }
+                    }
+                });
+
+                fingerprint = raw
+                    ? '!' + fingerprintId++
+                    : '!' + Object.keys(special).sort() + '|' + iehack + vendorId;
+                break;
+
+            case 'Raw':
+                fingerprint = '!' + declaration.value.value;
+                break;
+
+            default:
+                fingerprint = generate(declaration.value);
+        }
+
+        fingerprints[declarationId] = fingerprint;
+    }
+
+    return propertyName + fingerprint;
+}
+
+function needless(props, declaration, fingerprints) {
+    const property = resolveProperty(declaration.property);
+
+    if (NEEDLESS_TABLE.hasOwnProperty(property.basename)) {
+        const table = NEEDLESS_TABLE[property.basename];
+
+        for (const entry of table) {
+            const ppre = getPropertyFingerprint(property.prefix + entry, declaration, fingerprints);
+            const prev = props.hasOwnProperty(ppre) ? props[ppre] : null;
+
+            if (prev && (!declaration.important || prev.item.data.important)) {
+                return prev;
+            }
+        }
+    }
+}
+
+function processRule(rule, item, list, props, fingerprints) {
+    const declarations = rule.block.children;
+
+    declarations.forEachRight(function(declaration, declarationItem) {
+        const { property } = declaration;
+        const fingerprint = getPropertyFingerprint(property, declaration, fingerprints);
+        const prev = props[fingerprint];
+
+        if (prev && !dontRestructure.has(property)) {
+            if (declaration.important && !prev.item.data.important) {
+                props[fingerprint] = {
+                    block: declarations,
+                    item: declarationItem
+                };
+
+                prev.block.remove(prev.item);
+
+                // TODO: use it when we can refer to several points in source
+                // declaration.loc = {
+                //     primary: declaration.loc,
+                //     merged: prev.item.data.loc
+                // };
+            } else {
+                declarations.remove(declarationItem);
+
+                // TODO: use it when we can refer to several points in source
+                // prev.item.data.loc = {
+                //     primary: prev.item.data.loc,
+                //     merged: declaration.loc
+                // };
+            }
+        } else {
+            const prev = needless(props, declaration, fingerprints);
+
+            if (prev) {
+                declarations.remove(declarationItem);
+
+                // TODO: use it when we can refer to several points in source
+                // prev.item.data.loc = {
+                //     primary: prev.item.data.loc,
+                //     merged: declaration.loc
+                // };
+            } else {
+                declaration.fingerprint = fingerprint;
+
+                props[fingerprint] = {
+                    block: declarations,
+                    item: declarationItem
+                };
+            }
+        }
+    });
+
+    if (declarations.isEmpty) {
+        list.remove(item);
+    }
+}
+
+export default function restructBlock(ast) {
+    const stylesheetMap = {};
+    const fingerprints = Object.create(null);
+
+    walk(ast, {
+        visit: 'Rule',
+        reverse: true,
+        enter(node, item, list) {
+            const stylesheet = this.block || this.stylesheet;
+            const ruleId = (node.pseudoSignature || '') + '|' + node.prelude.children.first.id;
+            let ruleMap;
+            let props;
+
+            if (!stylesheetMap.hasOwnProperty(stylesheet.id)) {
+                ruleMap = {};
+                stylesheetMap[stylesheet.id] = ruleMap;
+            } else {
+                ruleMap = stylesheetMap[stylesheet.id];
+            }
+
+            if (ruleMap.hasOwnProperty(ruleId)) {
+                props = ruleMap[ruleId];
+            } else {
+                props = {};
+                ruleMap[ruleId] = props;
+            }
+
+            processRule.call(this, node, item, list, props, fingerprints);
+        }
+    });
+};
diff --git a/node_modules/csso/lib/restructure/7-mergeRuleset.js b/node_modules/csso/lib/restructure/7-mergeRuleset.js
new file mode 100644
index 00000000..8a4d5438
--- /dev/null
+++ b/node_modules/csso/lib/restructure/7-mergeRuleset.js
@@ -0,0 +1,86 @@
+import { walk } from 'css-tree';
+import { unsafeToSkipNode, isEqualDeclarations} from './utils.js';
+
+/*
+    At this step all rules has single simple selector. We try to join by equal
+    declaration blocks to first rule, e.g.
+
+    .a { color: red }
+    b { ... }
+    .b { color: red }
+    ->
+    .a, .b { color: red }
+    b { ... }
+*/
+
+function processRule(node, item, list) {
+    const selectors = node.prelude.children;
+    const declarations = node.block.children;
+    const nodeCompareMarker = selectors.first.compareMarker;
+    const skippedCompareMarkers = {};
+
+    list.nextUntil(item.next, function(next, nextItem) {
+        // skip non-ruleset node if safe
+        if (next.type !== 'Rule') {
+            return unsafeToSkipNode.call(selectors, next);
+        }
+
+        if (node.pseudoSignature !== next.pseudoSignature) {
+            return true;
+        }
+
+        const nextFirstSelector = next.prelude.children.head;
+        const nextDeclarations = next.block.children;
+        const nextCompareMarker = nextFirstSelector.data.compareMarker;
+
+        // if next ruleset has same marked as one of skipped then stop joining
+        if (nextCompareMarker in skippedCompareMarkers) {
+            return true;
+        }
+
+        // try to join by selectors
+        if (selectors.head === selectors.tail) {
+            if (selectors.first.id === nextFirstSelector.data.id) {
+                declarations.appendList(nextDeclarations);
+                list.remove(nextItem);
+                return;
+            }
+        }
+
+        // try to join by properties
+        if (isEqualDeclarations(declarations, nextDeclarations)) {
+            const nextStr = nextFirstSelector.data.id;
+
+            selectors.some((data, item) => {
+                const curStr = data.id;
+
+                if (nextStr < curStr) {
+                    selectors.insert(nextFirstSelector, item);
+                    return true;
+                }
+
+                if (!item.next) {
+                    selectors.insert(nextFirstSelector);
+                    return true;
+                }
+            });
+
+            list.remove(nextItem);
+            return;
+        }
+
+        // go to next ruleset if current one can be skipped (has no equal specificity nor element selector)
+        if (nextCompareMarker === nodeCompareMarker) {
+            return true;
+        }
+
+        skippedCompareMarkers[nextCompareMarker] = true;
+    });
+}
+
+export default function mergeRule(ast) {
+    walk(ast, {
+        visit: 'Rule',
+        enter: processRule
+    });
+};
diff --git a/node_modules/csso/lib/restructure/8-restructRuleset.js b/node_modules/csso/lib/restructure/8-restructRuleset.js
new file mode 100644
index 00000000..c9cbf094
--- /dev/null
+++ b/node_modules/csso/lib/restructure/8-restructRuleset.js
@@ -0,0 +1,176 @@
+import { List, walk } from 'css-tree';
+import {
+    unsafeToSkipNode,
+    isEqualSelectors,
+    compareDeclarations,
+    addSelectors
+} from './utils.js';
+
+function calcSelectorLength(list) {
+    return list.reduce((res, data) => res + data.id.length + 1, 0) - 1;
+}
+
+function calcDeclarationsLength(tokens) {
+    let length = 0;
+
+    for (const token of tokens) {
+        length += token.length;
+    }
+
+    return (
+        length +          // declarations
+        tokens.length - 1 // delimeters
+    );
+}
+
+function processRule(node, item, list) {
+    const avoidRulesMerge = this.block !== null ? this.block.avoidRulesMerge : false;
+    const selectors = node.prelude.children;
+    const block = node.block;
+    const disallowDownMarkers = Object.create(null);
+    let allowMergeUp = true;
+    let allowMergeDown = true;
+
+    list.prevUntil(item.prev, function(prev, prevItem) {
+        const prevBlock = prev.block;
+        const prevType = prev.type;
+
+        if (prevType !== 'Rule') {
+            const unsafe = unsafeToSkipNode.call(selectors, prev);
+
+            if (!unsafe && prevType === 'Atrule' && prevBlock) {
+                walk(prevBlock, {
+                    visit: 'Rule',
+                    enter(node) {
+                        node.prelude.children.forEach((data) => {
+                            disallowDownMarkers[data.compareMarker] = true;
+                        });
+                    }
+                });
+            }
+
+            return unsafe;
+        }
+
+        if (node.pseudoSignature !== prev.pseudoSignature) {
+            return true;
+        }
+
+        const prevSelectors = prev.prelude.children;
+
+        allowMergeDown = !prevSelectors.some((selector) =>
+            selector.compareMarker in disallowDownMarkers
+        );
+
+        // try prev ruleset if simpleselectors has no equal specifity and element selector
+        if (!allowMergeDown && !allowMergeUp) {
+            return true;
+        }
+
+        // try to join by selectors
+        if (allowMergeUp && isEqualSelectors(prevSelectors, selectors)) {
+            prevBlock.children.appendList(block.children);
+            list.remove(item);
+
+            return true;
+        }
+
+        // try to join by properties
+        const diff = compareDeclarations(block.children, prevBlock.children);
+
+        // console.log(diff.eq, diff.ne1, diff.ne2);
+
+        if (diff.eq.length) {
+            if (!diff.ne1.length && !diff.ne2.length) {
+                // equal blocks
+                if (allowMergeDown) {
+                    addSelectors(selectors, prevSelectors);
+                    list.remove(prevItem);
+                }
+
+                return true;
+            } else if (!avoidRulesMerge) { /* probably we don't need to prevent those merges for @keyframes
+                                              TODO: need to be checked */
+
+                if (diff.ne1.length && !diff.ne2.length) {
+                    // prevBlock is subset block
+                    const selectorLength = calcSelectorLength(selectors);
+                    const blockLength = calcDeclarationsLength(diff.eq); // declarations length
+
+                    if (allowMergeUp && selectorLength < blockLength) {
+                        addSelectors(prevSelectors, selectors);
+                        block.children.fromArray(diff.ne1);
+                    }
+                } else if (!diff.ne1.length && diff.ne2.length) {
+                    // node is subset of prevBlock
+                    const selectorLength = calcSelectorLength(prevSelectors);
+                    const blockLength = calcDeclarationsLength(diff.eq); // declarations length
+
+                    if (allowMergeDown && selectorLength < blockLength) {
+                        addSelectors(selectors, prevSelectors);
+                        prevBlock.children.fromArray(diff.ne2);
+                    }
+                } else {
+                    // diff.ne1.length && diff.ne2.length
+                    // extract equal block
+                    const newSelector = {
+                        type: 'SelectorList',
+                        loc: null,
+                        children: addSelectors(prevSelectors.copy(), selectors)
+                    };
+                    const newBlockLength = calcSelectorLength(newSelector.children) + 2; // selectors length + curly braces length
+                    const blockLength = calcDeclarationsLength(diff.eq); // declarations length
+
+                    // create new ruleset if declarations length greater than
+                    // ruleset description overhead
+                    if (blockLength >= newBlockLength) {
+                        const newItem = list.createItem({
+                            type: 'Rule',
+                            loc: null,
+                            prelude: newSelector,
+                            block: {
+                                type: 'Block',
+                                loc: null,
+                                children: new List().fromArray(diff.eq)
+                            },
+                            pseudoSignature: node.pseudoSignature
+                        });
+
+                        block.children.fromArray(diff.ne1);
+                        prevBlock.children.fromArray(diff.ne2overrided);
+
+                        if (allowMergeUp) {
+                            list.insert(newItem, prevItem);
+                        } else {
+                            list.insert(newItem, item);
+                        }
+
+                        return true;
+                    }
+                }
+            }
+        }
+
+        if (allowMergeUp) {
+            // TODO: disallow up merge only if any property interception only (i.e. diff.ne2overrided.length > 0);
+            // await property families to find property interception correctly
+            allowMergeUp = !prevSelectors.some((prevSelector) =>
+                selectors.some((selector) =>
+                    selector.compareMarker === prevSelector.compareMarker
+                )
+            );
+        }
+
+        prevSelectors.forEach((data) => {
+            disallowDownMarkers[data.compareMarker] = true;
+        });
+    });
+}
+
+export default function restructRule(ast) {
+    walk(ast, {
+        visit: 'Rule',
+        reverse: true,
+        enter: processRule
+    });
+};
diff --git a/node_modules/csso/lib/restructure/index.js b/node_modules/csso/lib/restructure/index.js
new file mode 100644
index 00000000..62c93528
--- /dev/null
+++ b/node_modules/csso/lib/restructure/index.js
@@ -0,0 +1,35 @@
+import prepare from './prepare/index.js';
+import mergeAtrule from './1-mergeAtrule.js';
+import initialMergeRuleset from './2-initialMergeRuleset.js';
+import disjoinRuleset from './3-disjoinRuleset.js';
+import restructShorthand from './4-restructShorthand.js';
+import restructBlock from './6-restructBlock.js';
+import mergeRuleset from './7-mergeRuleset.js';
+import restructRuleset from './8-restructRuleset.js';
+
+export default function(ast, options) {
+    // prepare ast for restructing
+    const indexer = prepare(ast, options);
+    options.logger('prepare', ast);
+
+    mergeAtrule(ast, options);
+    options.logger('mergeAtrule', ast);
+
+    initialMergeRuleset(ast);
+    options.logger('initialMergeRuleset', ast);
+
+    disjoinRuleset(ast);
+    options.logger('disjoinRuleset', ast);
+
+    restructShorthand(ast, indexer);
+    options.logger('restructShorthand', ast);
+
+    restructBlock(ast);
+    options.logger('restructBlock', ast);
+
+    mergeRuleset(ast);
+    options.logger('mergeRuleset', ast);
+
+    restructRuleset(ast);
+    options.logger('restructRuleset', ast);
+};
diff --git a/node_modules/csso/lib/restructure/prepare/createDeclarationIndexer.js b/node_modules/csso/lib/restructure/prepare/createDeclarationIndexer.js
new file mode 100644
index 00000000..227f8abf
--- /dev/null
+++ b/node_modules/csso/lib/restructure/prepare/createDeclarationIndexer.js
@@ -0,0 +1,31 @@
+import { generate } from 'css-tree';
+
+class Index {
+    constructor() {
+        this.map = new Map();
+    }
+    resolve(str) {
+        let index = this.map.get(str);
+
+        if (index === undefined) {
+            index = this.map.size + 1;
+            this.map.set(str, index);
+        }
+
+        return index;
+    }
+};
+
+export default function createDeclarationIndexer() {
+    const ids = new Index();
+
+    return function markDeclaration(node) {
+        const id = generate(node);
+
+        node.id = ids.resolve(id);
+        node.length = id.length;
+        node.fingerprint = null;
+
+        return node;
+    };
+};
diff --git a/node_modules/csso/lib/restructure/prepare/index.js b/node_modules/csso/lib/restructure/prepare/index.js
new file mode 100644
index 00000000..fc08082e
--- /dev/null
+++ b/node_modules/csso/lib/restructure/prepare/index.js
@@ -0,0 +1,41 @@
+import { walk, generate, keyword as resolveKeyword } from 'css-tree';
+import createDeclarationIndexer from './createDeclarationIndexer.js';
+import processSelector from './processSelector.js';
+
+export default function prepare(ast, options) {
+    const markDeclaration = createDeclarationIndexer();
+
+    walk(ast, {
+        visit: 'Rule',
+        enter(node) {
+            node.block.children.forEach(markDeclaration);
+            processSelector(node, options.usage);
+        }
+    });
+
+    walk(ast, {
+        visit: 'Atrule',
+        enter(node) {
+            if (node.prelude) {
+                node.prelude.id = null; // pre-init property to avoid multiple hidden class for generate
+                node.prelude.id = generate(node.prelude);
+            }
+
+            // compare keyframe selectors by its values
+            // NOTE: still no clarification about problems with keyframes selector grouping (issue #197)
+            if (resolveKeyword(node.name).basename === 'keyframes') {
+                node.block.avoidRulesMerge = true;  /* probably we don't need to prevent those merges for @keyframes
+                                                       TODO: need to be checked */
+                node.block.children.forEach(function(rule) {
+                    rule.prelude.children.forEach(function(simpleselector) {
+                        simpleselector.compareMarker = simpleselector.id;
+                    });
+                });
+            }
+        }
+    });
+
+    return {
+        declaration: markDeclaration
+    };
+};
diff --git a/node_modules/csso/lib/restructure/prepare/processSelector.js b/node_modules/csso/lib/restructure/prepare/processSelector.js
new file mode 100644
index 00000000..55a4fed8
--- /dev/null
+++ b/node_modules/csso/lib/restructure/prepare/processSelector.js
@@ -0,0 +1,97 @@
+import { generate } from 'css-tree';
+import specificity from './specificity.js';
+
+const nonFreezePseudoElements = new Set([
+    'first-letter',
+    'first-line',
+    'after',
+    'before'
+]);
+const nonFreezePseudoClasses = new Set([
+    'link',
+    'visited',
+    'hover',
+    'active',
+    'first-letter',
+    'first-line',
+    'after',
+    'before'
+]);
+
+export default function processSelector(node, usageData) {
+    const pseudos = new Set();
+
+    node.prelude.children.forEach(function(simpleSelector) {
+        let tagName = '*';
+        let scope = 0;
+
+        simpleSelector.children.forEach(function(node) {
+            switch (node.type) {
+                case 'ClassSelector':
+                    if (usageData && usageData.scopes) {
+                        const classScope = usageData.scopes[node.name] || 0;
+
+                        if (scope !== 0 && classScope !== scope) {
+                            throw new Error('Selector can\'t has classes from different scopes: ' + generate(simpleSelector));
+                        }
+
+                        scope = classScope;
+                    }
+
+                    break;
+
+                case 'PseudoClassSelector': {
+                    const name = node.name.toLowerCase();
+
+                    if (!nonFreezePseudoClasses.has(name)) {
+                        pseudos.add(`:${name}`);
+                    }
+
+                    break;
+                }
+
+                case 'PseudoElementSelector': {
+                    const name = node.name.toLowerCase();
+
+                    if (!nonFreezePseudoElements.has(name)) {
+                        pseudos.add(`::${name}`);
+                    }
+
+                    break;
+                }
+
+                case 'TypeSelector':
+                    tagName = node.name.toLowerCase();
+                    break;
+
+                case 'AttributeSelector':
+                    if (node.flags) {
+                        pseudos.add(`[${node.flags.toLowerCase()}]`);
+                    }
+
+                    break;
+
+                case 'Combinator':
+                    tagName = '*';
+                    break;
+            }
+        });
+
+        simpleSelector.compareMarker = specificity(simpleSelector).toString();
+        simpleSelector.id = null; // pre-init property to avoid multiple hidden class
+        simpleSelector.id = generate(simpleSelector);
+
+        if (scope) {
+            simpleSelector.compareMarker += ':' + scope;
+        }
+
+        if (tagName !== '*') {
+            simpleSelector.compareMarker += ',' + tagName;
+        }
+    });
+
+    // add property to all rule nodes to avoid multiple hidden class
+    node.pseudoSignature = pseudos.size > 0
+        ? [...pseudos].sort().join(',')
+        : false;
+};
diff --git a/node_modules/csso/lib/restructure/prepare/specificity.js b/node_modules/csso/lib/restructure/prepare/specificity.js
new file mode 100644
index 00000000..6fa4e5ab
--- /dev/null
+++ b/node_modules/csso/lib/restructure/prepare/specificity.js
@@ -0,0 +1,131 @@
+import { parse } from 'css-tree';
+
+function ensureSelectorList(node) {
+    if (node.type === 'Raw') {
+        return parse(node.value, { context: 'selectorList' });
+    }
+
+    return node;
+}
+
+function maxSpecificity(a, b) {
+    for (let i = 0; i < 3; i++) {
+        if (a[i] !== b[i]) {
+            return a[i] > b[i] ? a : b;
+        }
+    }
+
+    return a;
+}
+
+function maxSelectorListSpecificity(selectorList) {
+    return ensureSelectorList(selectorList).children.reduce(
+        (result, node) => maxSpecificity(specificity(node), result),
+        [0, 0, 0]
+    );
+}
+
+// §16. Calculating a selector’s specificity
+// https://www.w3.org/TR/selectors-4/#specificity-rules
+function specificity(simpleSelector) {
+    let A = 0;
+    let B = 0;
+    let C = 0;
+
+    // A selector’s specificity is calculated for a given element as follows:
+    simpleSelector.children.forEach((node) => {
+        switch (node.type) {
+            // count the number of ID selectors in the selector (= A)
+            case 'IdSelector':
+                A++;
+                break;
+
+            // count the number of class selectors, attributes selectors, ...
+            case 'ClassSelector':
+            case 'AttributeSelector':
+                B++;
+                break;
+
+            // ... and pseudo-classes in the selector (= B)
+            case 'PseudoClassSelector':
+                switch (node.name.toLowerCase()) {
+                    // The specificity of an :is(), :not(), or :has() pseudo-class is replaced
+                    // by the specificity of the most specific complex selector in its selector list argument.
+                    case 'not':
+                    case 'has':
+                    case 'is':
+                    // :matches() is used before it was renamed to :is()
+                    // https://github.com/w3c/csswg-drafts/issues/3258
+                    case 'matches':
+                    // Older browsers support :is() functionality as prefixed pseudo-class :any()
+                    // https://developer.mozilla.org/en-US/docs/Web/CSS/:is
+                    case '-webkit-any':
+                    case '-moz-any': {
+                        const [a, b, c] = maxSelectorListSpecificity(node.children.first);
+
+                        A += a;
+                        B += b;
+                        C += c;
+
+                        break;
+                    }
+
+                    // Analogously, the specificity of an :nth-child() or :nth-last-child() selector
+                    // is the specificity of the pseudo class itself (counting as one pseudo-class selector)
+                    // plus the specificity of the most specific complex selector in its selector list argument (if any).
+                    case 'nth-child':
+                    case 'nth-last-child': {
+                        const arg = node.children.first;
+
+                        if (arg.type === 'Nth' && arg.selector) {
+                            const [a, b, c] = maxSelectorListSpecificity(arg.selector);
+
+                            A += a;
+                            B += b + 1;
+                            C += c;
+                        } else {
+                            B++;
+                        }
+
+                        break;
+                    }
+
+                    // The specificity of a :where() pseudo-class is replaced by zero.
+                    case 'where':
+                        break;
+
+                    // The four Level 2 pseudo-elements (::before, ::after, ::first-line, and ::first-letter) may,
+                    // for legacy reasons, be represented using the <pseudo-class-selector> grammar,
+                    // with only a single ":" character at their start.
+                    // https://www.w3.org/TR/selectors-4/#single-colon-pseudos
+                    case 'before':
+                    case 'after':
+                    case 'first-line':
+                    case 'first-letter':
+                        C++;
+                        break;
+
+                    default:
+                        B++;
+                }
+                break;
+
+            // count the number of type selectors ...
+            case 'TypeSelector':
+                // ignore the universal selector
+                if (!node.name.endsWith('*')) {
+                    C++;
+                }
+                break;
+
+            // ... and pseudo-elements in the selector (= C)
+            case 'PseudoElementSelector':
+                C++;
+                break;
+        }
+    });
+
+    return [A, B, C];
+};
+
+export default specificity;
diff --git a/node_modules/csso/lib/restructure/utils.js b/node_modules/csso/lib/restructure/utils.js
new file mode 100644
index 00000000..792cc59b
--- /dev/null
+++ b/node_modules/csso/lib/restructure/utils.js
@@ -0,0 +1,142 @@
+const { hasOwnProperty } = Object.prototype;
+
+export function isEqualSelectors(a, b) {
+    let cursor1 = a.head;
+    let cursor2 = b.head;
+
+    while (cursor1 !== null && cursor2 !== null && cursor1.data.id === cursor2.data.id) {
+        cursor1 = cursor1.next;
+        cursor2 = cursor2.next;
+    }
+
+    return cursor1 === null && cursor2 === null;
+}
+
+export function isEqualDeclarations(a, b) {
+    let cursor1 = a.head;
+    let cursor2 = b.head;
+
+    while (cursor1 !== null && cursor2 !== null && cursor1.data.id === cursor2.data.id) {
+        cursor1 = cursor1.next;
+        cursor2 = cursor2.next;
+    }
+
+    return cursor1 === null && cursor2 === null;
+}
+
+export function compareDeclarations(declarations1, declarations2) {
+    const result = {
+        eq: [],
+        ne1: [],
+        ne2: [],
+        ne2overrided: []
+    };
+
+    const fingerprints = Object.create(null);
+    const declarations2hash = Object.create(null);
+
+    for (let cursor = declarations2.head; cursor; cursor = cursor.next)  {
+        declarations2hash[cursor.data.id] = true;
+    }
+
+    for (let cursor = declarations1.head; cursor; cursor = cursor.next)  {
+        const data = cursor.data;
+
+        if (data.fingerprint) {
+            fingerprints[data.fingerprint] = data.important;
+        }
+
+        if (declarations2hash[data.id]) {
+            declarations2hash[data.id] = false;
+            result.eq.push(data);
+        } else {
+            result.ne1.push(data);
+        }
+    }
+
+    for (let cursor = declarations2.head; cursor; cursor = cursor.next)  {
+        const data = cursor.data;
+
+        if (declarations2hash[data.id]) {
+            // when declarations1 has an overriding declaration, this is not a difference
+            // unless no !important is used on prev and !important is used on the following
+            if (!hasOwnProperty.call(fingerprints, data.fingerprint) ||
+                (!fingerprints[data.fingerprint] && data.important)) {
+                result.ne2.push(data);
+            }
+
+            result.ne2overrided.push(data);
+        }
+    }
+
+    return result;
+}
+
+export function addSelectors(dest, source) {
+    source.forEach((sourceData) => {
+        const newStr = sourceData.id;
+        let cursor = dest.head;
+
+        while (cursor) {
+            const nextStr = cursor.data.id;
+
+            if (nextStr === newStr) {
+                return;
+            }
+
+            if (nextStr > newStr) {
+                break;
+            }
+
+            cursor = cursor.next;
+        }
+
+        dest.insert(dest.createItem(sourceData), cursor);
+    });
+
+    return dest;
+}
+
+// check if simpleselectors has no equal specificity and element selector
+export function hasSimilarSelectors(selectors1, selectors2) {
+    let cursor1 = selectors1.head;
+
+    while (cursor1 !== null) {
+        let cursor2 = selectors2.head;
+
+        while (cursor2 !== null) {
+            if (cursor1.data.compareMarker === cursor2.data.compareMarker) {
+                return true;
+            }
+
+            cursor2 = cursor2.next;
+        }
+
+        cursor1 = cursor1.next;
+    }
+
+    return false;
+}
+
+// test node can't to be skipped
+export function unsafeToSkipNode(node) {
+    switch (node.type) {
+        case 'Rule':
+            // unsafe skip ruleset with selector similarities
+            return hasSimilarSelectors(node.prelude.children, this);
+
+        case 'Atrule':
+            // can skip at-rules with blocks
+            if (node.block) {
+                // unsafe skip at-rule if block contains something unsafe to skip
+                return node.block.children.some(unsafeToSkipNode, this);
+            }
+            break;
+
+        case 'Declaration':
+            return false;
+    }
+
+    // unsafe by default
+    return true;
+}