lib/Tokenizer.php
protected function _checkSelectors($words) {
        $selectors = $this->_getSelectors($words);
        $result = [
            'token' => '{',
            'code'  => $this->_mergeWords($words),
            'index' => $words[0]['index'],
        ];

        if (!count($selectors)) {
            return $result;
        }

        if (substr($selectors[0], 0, 1) === '@') {
            $split = preg_split('/\s+/', $selectors[0]);
            $result['atRule'] = substr($split[0], 1);
            $selectors[0] = trim(substr($selectors[0], 1 + strlen($result['atRule'])));
            $result['atValues'] = $selectors;
        } else {
            $result['selectors'] = $selectors;
        }

        return $result;
    }
protected function _checkSelectors($words) {
        $selectors = $this->_getSelectors($words);
        $result = [
            'token' => '{',
            'code'  => $this->_mergeWords($words),
            'index' => $words[0]['index'],
        ];

        if (!count($selectors)) {
            return $result;
        }

        if (substr($selectors[0], 0, 1) === '@') {
            $split = preg_split('/\s+/', $selectors[0]);
            $result['atRule'] = substr($split[0], 1);
            $selectors[0] = trim(substr($selectors[0], 1 + strlen($result['atRule'])));
            $result['atValues'] = $selectors;
        } else {
            $result['selectors'] = $selectors;
        }

        return $result;
    }
Get token with selectors list

@param array $words
@return array