src/language-css/parser-postcss.js/parseSelector
function parseSelector(selector) {
  // If there's a comment inside of a selector, the parser tries to parse
  // the content of the comment as selectors which turns it into complete
  // garbage. Better to print the whole selector as-is and not try to parse
  // and reformat it.
  if (selector.match(/\/\/|\/\*/)) {
    return {
      type: "selector-comment",
      value: selector.replace(/^ +/, "").replace(/ +$/, "")
    };
  }
  const selectorParser = require("postcss-selector-parser");
  let result;
  selectorParser(result_ => {
    result = result_;
  }).process(selector);
  return addTypePrefix(result, "selector-");
}