code: function _appendSelector(originSelector, targetRule, value) {
    const originSelectors = _parseSelectors(originSelector);
    let targetRuleSelectors = _parseSelectors(targetRule.selector);
    targetRuleSelectors.forEach((targetRuleSelector) => {
      [].push.apply(targetRuleSelectors, originSelectors.map(newOriginSelector =>
        _replaceSelector(targetRuleSelector, value, newOriginSelector)));
    });
    // removes duplicate selectors
    targetRuleSelectors = [...new Set(targetRuleSelectors)];
    targetRule.selector = _assembleSelectors(targetRuleSelectors);
  }
docs: Private: appends selector from originRule to matching rules.
  Does not return a value, but it transforms the PostCSS AST.
  
  * `originSelector` {String} selector from originRule to append
  * `targetRule` {Object} PostCSS Rule that matched value.
  Will have originSelector appended to it
  * `value` {String} inherit declaration value