function replaceWithPlainText(selector, regex) {
  return selector.replace(regex, function(match) {
    return Array(match.length + 1).join('A');
  });
}
Replace escaped characters with plain text, using the "A" character.
@see https://www.w3.org/TR/CSS21/syndata.html#characters
@param {string} selector
@param {!RegExp} regex
@return {string}