code: function (name) {
      // pre-test to improve performance
      if (REGEXP_IS_ESCAPED.test(name)) {
          name = name.replace(REGEXP_DOT, '.');
          name = name.replace(REGEXP_DOLLAR, '$');
          name = name.replace(REGEXP_TO_BSON, 'toBSON');
          name = name.replace(REGEXP_BSON_TYPE, '_bsontype');
      }
  
      return name;
  }
docs: Reverses a string transformed using _escapePropertyName() back to its original form.
  Note that the reverse transformation might not be 100% correct for certain unlikely-to-occur strings
  (e.g. string contain null chars).
  @param key
  @returns {*}
  @private